wdiff draft-ietf-taps-transports-usage-02.txt draft-ietf-taps-transports-usage-03.txt

TAPS M. Welzl
Internet-Draft University of Oslo
Intended status: Informational M. Tuexen
Expires: May 4, September 9, 2017 Muenster Univ. of Appl. Sciences
N. Khademi
University of Oslo
October 31, 2016
March 8, 2017

On the Usage of Transport Service Features Provided by IETF Transport Protocols
draft-ietf-taps-transports-usage-02
draft-ietf-taps-transports-usage-03

Abstract

This document describes how transport protocols TCP, MPTCP, SCTP, UDP and UDP-Lite expose
services to applications and how an application can configure and use
the
features of a transport service. features that make up these services. It also
discusses the service provided by the LEDBAT congestion control
mechanism.

Status of this Memo

This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.

Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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and may be updated, replaced, or obsoleted by other documents at any
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This Internet-Draft will expire on May 4, September 9, 2017.

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(http://trustee.ietf.org/license-info) in effect on the date of
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Table of Contents

1. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Pass 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1. Primitives Provided by TCP . . . . . . . . . . . . . . . . 5
3.1.1. Excluded Primitives or Parameters . . . . . . . . . . 7 8
3.2. Primitives Provided by MPTCP . . . . . . . . . . . . . . . 8 9
3.3. Primitives Provided by SCTP . . . . . . . . . . . . . . . 9 10
3.3.1. Excluded Primitives or Parameters . . . . . . . . . . 13 17
3.4. Primitives Provided by UDP and UDP-Lite . . . . . . . . . 14 17
3.5. The service of LEDBAT . . . . . . . . . . . . . . . . . . 17
4. Pass 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 18
4.1. CONNECTION Related Primitives . . . . . . . . . . . . . . 14 19
4.2. DATA Transfer Related Primitives . . . . . . . . . . . . . 23 30
5. Pass 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 33
5.1. CONNECTION Related Transport Service Features . . . . . . 25 . . . . 33
5.2. DATA Transfer Related Transport Service Features . . . . . 30 . . . . 39
5.2.1. Sending Data . . . . . . . . . . . . . . . . . . . . . 30 39
5.2.2. Receiving Data . . . . . . . . . . . . . . . . . . . . 31 40
5.2.3. Errors . . . . . . . . . . . . . . . . . . . . . . . . 31 40
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 32 41
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 32 41
8. Security Considerations . . . . . . . . . . . . . . . . . . . 32 41
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 32 41
9.1. Normative References . . . . . . . . . . . . . . . . . . . 32 41
9.2. Informative References . . . . . . . . . . . . . . . . . . 33 44
Appendix A. Overview of RFCs used as input for pass 1 . . . . . . 35 45
Appendix B. How to contribute . . . . . . . this document was developed . . . . . . . . . . . 36 45
Appendix C. Revision information . . . . . . . . . . . . . . . . 37 47
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 38 47

1. Terminology

Transport Service Feature: a specific end-to-end feature that a the transport service
layer provides to its clients. an application. Examples include
confidentiality, reliable delivery, ordered delivery, message-
versus-stream orientation, etc.
Transport Service: a set of transport service features, Transport Features, without an
association to any given framing protocol, which provides a
complete service to an application.
Transport Protocol: an implementation that provides one or more
different transport services using a specific framing and header
format on the wire.
Transport Protocol Component: an implementation of a transport
service feature Transport
Feature within a protocol.
Transport Service Instance: an arrangement of transport protocols
with a selected set of features and configuration parameters that
implements a single transport service, e.g., a protocol stack (RTP
over UDP).
Application: an entity that uses the transport layer for end-to-end
delivery of data across the network (this may also be an upper
layer protocol or tunnel encapsulation).
Endpoint: an entity that communicates with one or more other
endpoints using a transport protocol.
Connection: shared state of two or more endpoints that persists
across messages that are transmitted between these endpoints.
Primitive: a function call that is used to locally communicate
between an application and a transport endpoint and is related to
one or more Transport Service Features.
Parameter: a value passed between an application and a transport
protocol by a primitive.
Socket: the combination of a destination IP address and a
destination port number.
Transport Address: the combination of an IP address, transport
protocol and the port number used by the transport protocol.

2. Introduction

This document presents defined interactions between applications and
the transport protocols TCP, MPTCP, SCTP, UDP and applications UDP-Lite as well as
the LEDBAT congestion control mechanism in the form of 'primitives' (function
calls). primitives and
Transport Features. Primitives can be invoked by an application or a
transport protocol; the latter type is called an "event". The list
of
transport service features and primitives and Transport Features in this document is strictly
based on the parts of protocol specifications that relate to describe what the
protocol provides to an application using it and how the application
interacts with it. It does not cover parts

Parts of a protocol that are explicitly stated as optional to implement.
implement are not covered. Interactions between the application and
a transport protocol that are not directly related to the operation
of the protocol are also not covered. For example, [RFC6458]
explains how an application can use socket options to indicate its
interest in receiving certain notifications. However, for the
purpose of identifying primitives and Transport Services, the ability
to enable or disable the reception of notifications is irrelevant.
Similarly, one-to-many style sockets described in [RFC6458] just
affect the application programming style, not how the underlying
protocol operates, and they are therefore not discussed here. The
same is true for the ability to obtain the unchanged value of a
parameter that an application has previously set (this is the case
for the "get" in many get/set operations in [RFC6458]).

The document presents a three-pass process to arrive at a list of
transport service features. In
Transport Features. In the first pass, the relevant RFC text is
discussed per protocol. In the second pass, this discussion is used
to derive a list of primitives that are uniformly categorized across
protocols. Here, an attempt is made to present or -- where text
describing primitives does not yet exist -- construct primitives in a
slightly generalized form to highlight similarities. This is, for
example, achieved by renaming primitives of protocols or by avoiding
a strict 1:1-mapping between the primitives in the protocol
specification and primitives in the list. Finally, the third pass
presents transport service features Transport Features based on pass 2, identifying which
protocols implement them.

In the list resulting from the second pass, some transport service
features Transport Features
are missing because they are implicit in some protocols, and they
only become explicit when we consider the superset of all features
offered by all protocols. For example, TCP's reliability
includes integrity via a checksum, but TCP always carries out
congestion control; we have to include consider it together with a protocol
like UDP-Lite as specified in [RFC3828] UDP (which has a configurable
checksum) in the list does not have congestion control) before we can
consider an always-on checksum congestion control as a transport service feature. Similar arguments apply to other
protocol functions (e.g. congestion control). Transport Feature. The complete
list of features across all protocols is therefore only available
after pass 3.

This document discusses unicast transport protocols. [AUTHOR'S NOTE:
we skip "congestion control mechanisms" for now. This simplifies the
discussion; the protocols and a unicast
congestion control mechanisms part is about LEDBAT,
which should be easy to add later.] mechanism. Transport protocols provide
communication between processes that operate on network endpoints,
which means that they allow for multiplexing of communication between
the same IP addresses, and normally this multiplexing is achieved
using port numbers. Port multiplexing is therefore assumed to be
always provided and not discussed in this document.

Some protocols are connection-oriented. Connection-oriented
protocols often use an initial call to a specific transport primitive
to open a connection before communication can progress, and require
communication to be explicitly terminated by issuing another call to
a transport primitive (usually called "close"). A "connection" is
the common state that some transport primitives refer to, e.g., to
adjust general configuration settings. Connection establishment,
maintenance and termination are therefore used to categorize
transport primitives of connection-oriented transport protocols in
pass 2 and pass 3. For this purpose, UDP is assumed to be used with
"connected" sockets, i.e. sockets that are bound to a specific pair
of addresses and ports [FJ16].

3. Pass 1

This first iteration summarizes the relevant text parts of the RFCs
describing the protocols, focusing on what each transport protocol
provides to the application and how it is used (abstract API
descriptions, where they are available).

3.1. Primitives Provided by TCP

[RFC0793] states: "The Transmission Control Protocol (TCP) is
intended for use as a highly reliable host-to-host protocol between
hosts in packet-switched computer communication networks, and in
interconnected systems of such networks". Section 3.8 in [RFC0793]
further specifies the interaction with the application by listing
several transport primitives. It is also assumed that an Operating
System provides a means for TCP to asynchronously signal the
application; the primitives representing such signals are called
'events' in this section. This section describes the relevant
primitives.

open: this is either active or passive, to initiate a connection or
listen for incoming connections. All other primitives are
associated with a specific connection, which is assumed to first
have been opened. An active open call contains a socket. A
passive open call with a socket waits for a particular connection;
alternatively, a passive open call can leave the socket
unspecified to accept any incoming connection. A fully specified
passive call can later be made active by calling 'send'.
Optionally, a timeout can be specified, after which TCP will abort
the connection if data has not been successfully delivered to the
destination (else a default timeout value is used). [RFC1122]
describes a procedure for aborting the connection that must be
used to avoid excessive retransmissions, and states that an
application must be able to control the threshold used to
determine the condition for aborting -- and that this threshold
may be measured in time units or as a count of retransmission.

This indicates that the timeout could also be specified as a count
of retransmission.

Also optional, for multihomed hosts, the local IP address can be
provided [RFC1122]. If it is not provided, a default choice will
be made in case of active open calls. A passive open call will
await incoming connection requests to all local addresses and then
maintain usage of the local IP address where the incoming
connection request has arrived. Finally, the 'options' parameter
is explained in [RFC1122] to allow the application to specify IP
options such as source route, record route, or timestamp. It is
not stated on which segments of a connection these options should
be applied, but probably all segments, as this is also stated in a
specification given for the usage of source route (section 4.2.3.8
of [RFC1122]). Source route is the only non-optional IP option in
this parameter, allowing an application to specify a source route
when it actively opens a TCP connection.

send: this is the primitive that an application uses to give the
local TCP transport endpoint a number of bytes that TCP should
reliably send to the other side of the connection. The URGENT
flag, if set, states that the data handed over by this send call
is urgent and this urgency should be indicated to the receiving
process in case the receiving application has not yet consumed all
non-urgent data preceding it. An optional timeout parameter can
be provided that updates the connection's timeout (see 'open').

receive: This primitive allocates a receiving buffer for a provided
number of bytes. It returns the number of received bytes provided
in the buffer when these bytes have been received and written into
the buffer by TCP. The application is informed of urgent data via
an URGENT flag: if it is on, there is urgent data. If it is off,
there is no urgent data or this call to 'receive' has returned all
the urgent data.

close: This primitive closes one side of a connection. It is
semantically equivalent to "I have no more data to send" but does
not mean "I will not receive any more", as the other side may
still have data to send. This call reliably delivers any data
that has already been given to TCP (and if that fails, 'close'
becomes 'abort').

abort: This primitive causes all pending 'send' and 'receive' calls
to be aborted. A TCP RESET message is sent to the TCP endpoint on
the other side of the connection [RFC0793].

close event: TCP uses this primitive to inform an application that
the application on the other side has called the 'close'
primitive, so the local application can also issue a 'close' and
terminate the connection gracefully. See [RFC0793], Section 3.5.

abort event: When TCP aborts a connection upon receiving a "Reset"
from the peer, it "advises the user and goes to the CLOSED state."
See [RFC0793], Section 3.4.

USER TIMEOUT event: This event, described in Section 3.9 of
[RFC0793], is executed when the user timeout expires (see 'open').
All queues are flushed and the application is informed that the
connection had to be aborted due to user timeout.

ERROR_REPORT event: This event, described in Section 4.2.4.1 of
[RFC1122], informs the application of "soft errors" that can be
safely ignored [RFC5461], including the arrival of an ICMP error
message or excessive retransmissions (reaching a threshold below
the threshold where the connection is aborted).

Type-of-Service: Section 4.2.4.2 of [RFC1122] states that the
application layer MUST be able to specify the Type-of-Service
(TOS) for segments that are sent on a connection. The application
should be able to change the TOS during the connection lifetime,
and the TOS value should be passed to the IP layer unchanged.
Since then the TOS field has been redefined. A part of the field
has been assigned to ECN [RFC3168] and the six most significant
bits have been assigned to carry the DiffServ CodePoint, DSField
[RFC3260]. Staying with the intention behind the application's
ability to specify the "Type of Service", this should probably be
interpreted to mean the value in the DSField, which is the
Differentiated Services Codepoint (DSCP).

Nagle: The Nagle algorithm, described in Section 4.2.3.4 of
[RFC1122], delays sending data for some time to increase the
likelihood of sending a full-sized segment. An application can
disable the Nagle algorithm for an individual connection.

User Timeout Option: The User Timeout Option (UTO) [RFC5482] allows
one end of a TCP connection to advertise its current user timeout
value so that the other end of the TCP connection can adapt its
own user timeout accordingly. In addition to the configurable
value of the User Timeout (see 'send'), [RFC5482] introduces three
per-connection state variables that an application can adjust to
control the operation of the User Timeout Option (UTO): ADV_UTO is
the value of the UTO advertised to the remote TCP peer (default:
system-wide default user timeout); ENABLED (default false) is a
boolean-type flag that controls whether the UTO option is enabled
for a connection. This applies to both sending and receiving.
CHANGEABLE is a boolean-type flag (default true) that controls
whether the user timeout may be changed based on a UTO option
received from the other end of the connection. CHANGEABLE becomes
false when an application explicitly sets the user timeout (see
'send').

Fast Open: TCP Fast Open (TFO) [RFC7413] allows to immediately hand
over a message from the active open to the passive open side of a
TCP connection together with the first message establishment
packet (the SYN). This can be useful for applications that are
sensitive to TCP's connection setup delay. TCP implementations
MUST NOT use TFO by default, but only use TFO if requested
explicitly by the application on a per-service-port basis. To
benefit from TFO, the first application data unit (e.g., an HTTP
request) needs to be no more than TCP's maximum segment size
(minus options used in the SYN). For the active open side,
[RFC7413] recommends changing or replacing the connect() call in
order to support a user data buffer argument. For the passive
open side, the application needs to enable the reception of Fast
Open requests, e.g. via a new TCP_FASTOPEN setsockopt() socket
option before listen(). The receiving application must be
prepared to accept duplicates of the TFO message, as the first
data written to a socket can be delivered more than once to the
application on the remote host.

3.1.1. Excluded Primitives or Parameters

The 'open' primitive specified in [RFC0793] can be handed optional
Precedence or security/compartment information according to
[RFC0793], but this was not included here because it is mostly
irrelevant today, as explained in [RFC7414].

The 'status' primitive was not included because [RFC0793] describes
this primitive as "implementation dependent" and states that it
"could be excluded without adverse effect". Moreover, while a data
block containing specific information is described, it is also stated
that not all of this information may always be available. The 'send'
primitive described in [RFC0793] includes an optional PUSH flag
which, if set, requires data to be promptly transmitted to the
receiver without delay; the 'receive' primitive described in
[RFC0793] can (under some conditions) yield the status of the PUSH
flag. Because PUSH functionality is made optional to implement for
both the 'send' and 'receive' primitives in [RFC1122], this
functionality is not included here. [RFC1122] also introduces keep-
alives to TCP, but these are optional to implement and hence not
considered here. [RFC1122] describes that "some TCP implementations
have included a FLUSH call", indicating that this call is also
optional to implement. It is therefore not considered here.

3.2. Primitives Provided by MPTCP

Multipath TCP (MPTCP) is an extension to TCP that allows the use of
multiple paths for a single data-stream. It achieves this by
creating different so-called TCP subflows for each of the interfaces
and scheduling the traffic across these TCP subflows. The service
provided by MPTCP is described in [RFC6182] "Multipath TCP MUST
follow the same service model as TCP [RFC0793]: in- order, reliable,
and byte-oriented delivery. Furthermore, a Multipath TCP connection
SHOULD provide the application with no worse throughput or resilience
than it would expect from running a single TCP connection over any
one of its available paths."

Further, [RFC6182] states constraints on the API exposed by MPTCP: "A
multipath-capable equivalent of TCP MUST retain some level of
backward compatibility with existing TCP APIs, so that existing
applications can use the newer merely by upgrading the operating
systems of the end hosts." As such, the primitives provided by MPTCP
are equivalent to the ones provided by TCP. Nevertheless, [RFC6824]
and [RFC6897] clarify some parts of TCP's primitives with respect to
MPTCP and add some extensions for better control on MPTCP's subflows.
Hereafter is a list of the clarifications and extensions the above
cited RFCs provide to TCP's primitives.

open: [RFC6897] states "An application should be able to request to
turn on or turn off the usage of MPTCP.". The RFC states that
this functionality can be provided through a socket-option called
TCP_MULTIPATH_ENABLE. Further, [RFC6897] says that MPTCP must be
disabled in case the application is binding to a specific address.

send/receive: [RFC6824] states that the sending and receiving of
data does not require any changes to the application when MPTCP is
being used. The MPTCP-layer will "take one input data stream from
an application, and split it into one or more subflows, with
sufficient control information to allow it to be reassembled and
delivered reliably and in order to the recipient application."
The use of the Urgent-Pointer is special in MPTCP and [RFC6824]
says "a TCP subflow MUST NOT use the Urgent Pointer to interrupt
an existing mapping."

address and subflow management: MPTCP uses different addresses and
allows a host to announce these addresses as part of the protocol.
[RFC6897] says "An application should be able to restrict MPTCP to
binding to a given set of addresses." and thus allows applications
to limit the set of addresses that are being used by MPTCP.

Further, "An application should be able to obtain information on
the pairs of addresses used by the MPTCP subflows.".

3.3. Primitives Provided by SCTP

Section 1.1 of [RFC4960] lists limitations of TCP that SCTP removes.
Three of the four mentioned limitations directly translate into a
transport service features
Transport Features that are visible to an application using SCTP: 1)
it allows for preservation of message delineations; 2) these
messages, while reliably transferred, do not require to be in order
unless the application wants it; 3) multi-homing is supported. In
SCTP, connections are called "association" "associations" and they can be between
not only two (as in TCP) but multiple addresses at each endpoint.

Section 10 of [RFC4960] further specifies the interaction with the
application (which RFC [RFC4960] calls the "Upper Layer Protocol"
(ULP)). It is assumed that the Operating System provides a means for
SCTP to asynchronously signal the application; the primitives
representing such signals are called 'events' in this section. Here,
we describe the relevant primitives. In addition to the abstract API
described in Section 10 of [RFC4960], an extension to the socket API
is described in [RFC6458] [RFC6458], covering the functionality of the base
protocol specified in [RFC4960] and its extensions specified in
[RFC3758], [RFC4895], and [RFC5061]. For the protocol extensions
specified in [RFC6525], [RFC6951], [RFC7053], [RFC7496], and [RFC7829]
and [I-D.ietf-tsvwg-sctp-ndata], the corresponding extensions of the
socket API are specified in these protocol specifications. The
functionality exposed to the ULP through this socket API is
considered here in addition to the abstract API specified in Section
10 of [RFC4960].

Initialize: Initialize

[RFC4960] contains a "SETPROTOCOLPARAMETERS" primitive that allows to
adjust elements of a parameter list; it is stated that SCTP
implementations "may allow ULP to customize some of these protocol
parameters", indicating that none of the elements of this parameter
list are mandatory to make ULP-configurable. Thus, we only consider
the parameters in [RFC4960] that are also covered in one of the other
RFCs listed above, which leads us to exclude the parameters
RTO.Alpha, RTO.Beta and HB.Max.Burst. For clarity, we also replace
"SETPROTOCOLPARAMETERS" itself with primitives that adjust parameters
or groups of parameters which fit together.

Initialize: Initialize, described in [RFC4960], creates a local SCTP
instance that it binds to a set of local addresses (and, if
provided, port number). Initialize needs to be called only once
per set of local addresses. [RFC6458] also describes a number of
per-association initialization parameters that can be used when an
association is created, but before it is connected (via the
primitive 'Associate' below): the maximum number of inbound
streams the application is prepared to support, the maximum number
of attempts to be made when sending the INIT (the first message of
association establishment), and the maximum retransmission timeout
(RTO) value to use when attempting an INIT. At this point, before
connecting, an application can also enable UDP encapsulation by
configuring the remote UDP encapsulation port number [RFC6951].

Associate: This creates an association (the SCTP equivalent of a
connection) between that connects the local SCTP instance and a remote
SCTP instance. To identify the remote endpoint, it can be given
one or multiple (using connectx as described in section 9.9 of
[RFC6458]) sockets. Most primitives are associated with a
specific association, which is assumed to first have been created.
Associate can return a list of destination transport addresses so
that multiple paths can later be used. One of the returned
sockets will be selected by the local endpoint as default primary
path for sending SCTP packets to this peer, but this choice can be
changed by the application using the list of destination
addresses. Associate is also given the number of outgoing streams
to request and optionally returns the number of negotiated
outgoing streams
negotiated. streams. An optional parameter of 32-bits, 32 bits, the
adaptation layer indication, can be provided, as specified in
[RFC5061]. If the extension specified in [RFC4895] is used, the
chunk types required to be sent authenticated by the peer can be
provided. [RFC6458] describes a 'SCTP_CANT_STR_ASSOC'
notification that is used to inform the application of a failure
to create an association. [RFC6458] describes how an application
could use sendto() or sendmsg() to implicitly setup an
association, thereby handing over a message that SCTP might send
during the association setup phase. Note that this mechanism is
different from TCP's TFO mechanism: the message would arrive only
once, after at least one RTT, as it is sent together with the
third message exchanged during association setup, the COOKIE-ECHO
chunk).

Send: This sends a message of a certain length in bytes over an
association. A number can be provided to later refer to the
correct message when reporting an error, and a stream id is
provided to specify the stream to be used inside an association
(we consider this as a mandatory parameter here for simplicity: if
not provided, the stream id defaults to 0). A condition to
abandon the message can be specified (for example limiting the
number of retransmissions or the lifetime of the user message).
This allows to control the partial reliability extension specified
in [RFC3758] and [RFC7496]. An optional maximum life time can
specify the time after which the message should be discarded
rather than sent. A choice (advisory, i.e. not guaranteed) of the
preferred path can be made by providing a socket, and the message
can be delivered out-of-order if the unordered flag is set. An
advisory flag indicates that the peer should not delay the
acknowledgement of the user message provided by making use of the
I-bit specified in [RFC7053]. Another advisory flag indicates
whether the application prefers to avoid bundling user data with
other outbound DATA chunks (i.e., in the same packet). A payload
protocol-id can be provided to pass a value that indicates the
type of payload protocol data to the peer. If the extension
specified in [RFC4895] is used, the key identifier used for
authenticating the DATA chunks can be provided.

Receive: Messages are received from an association, and optionally a
stream within the association, with their size returned. The
application is notified of the availability of data via a DATA
ARRIVE notification. If the sender has included a payload
protocol-id, this value is also returned. If the received message
is only a partial delivery of a whole message, a partial flag will
indicate so, in which case the stream id and a stream sequence
number are provided to the application. A delivery number lets
the application detect reordering.

Shutdown: This primitive gracefully closes an association, reliably
delivering any data that has already been handed over to SCTP. A
return code informs about
parameter lets the application control whether further receive or
send operations or both are disabled when the call is issued. A
return code informs about success or failure of this procedure.

Abort: This ungracefully closes an association, by discarding any
locally queued data and informing the peer that the association
was aborted. Optionally, an abort reason to be passed to the peer
may be provided by the application. A return code informs about
success or failure of this procedure.

Change Heartbeat / Request Heartbeat: This allows the application to
enable/disable heartbeats and optionally specify a heartbeat
frequency as well as requesting a single heartbeat to be carried
out upon a function call, with a notification about success or
failure of transmitting the HEARTBEAT chunk to the destination.

Set Protocol Parameters: This allows to set values for protocol
parameters per association; for some parameters, a setting can be
made per socket.

Configure Max. Retransmissions of an Association: The set listed parameter
Association.Max.Retrans in [RFC4960] is: RTO.Initial;
RTO.Min; RTO.Max; Max.Burst; RTO.Alpha; RTO.Beta;
Valid.Cookie.Life; Association.Max.Retrans; Path.Max.Retrans;
Max.Init.Retransmits; HB.interval; HB.Max.Burst. In addition to
these, the Quick Failover Algorithm specified [RFC4960], called sasoc_maxrxt in [RFC7829] can be
controlled by
[RFC6458], allows to configure the PotentiallyFailed.Max.Retrans and
Primary.Switchover.Max.Retrans parameter. A remote UDP
encapsulation port can be set for using UDP encapsulation number of unsuccessful
retransmissions after which an entire association is considered as
specified in [RFC6951].
failed (which should invoke a COMMUNICATION LOST notification).

Set Primary: This allows to set a new primary default path for an
association by providing a socket. Optionally, a default source
address to be used in IP datagrams can be provided.

Set / Get Authentication Parameters: This allows an endpoint to add/
remove key material to/from an association. In addition, the
chunk types being authenticated can be queried. This is provided
by the protocol extension defined in [RFC4895].

Change Local Address / Set Peer Primary: This allows an endpoint to
add/remove local addresses to/from an association. In addition,
the peer can be given a hint which address to use as the primary
address. This is provided by the protocol extension defined in
[RFC5061].

Add / Reset Streams, Reset Association:

Configure Path Switchover: [RFC4960] contains a primitive called SET
FAILURE THRESHOLD. This allows an endpoint to
add streams to an existing association or or to reset them
individually. Additionally, configures the association can be reset. This parameter
"Path.Max.Retrans", which determines after how many
retransmissions a particular transport address is provided by the protocol extension defined considered as
unreachable. If there are more transport addresses available in [RFC6525].

Status: The 'Status' primitive returns
an association, reaching this limit will invoke a data block path switchover.
[RFC7829] extends this method with information
about a specified association, containing: association connection
state; socket list; destination transport address reachability
states; current receiver window size; current congestion window
sizes; number of unacknowledged DATA chunks; number concept of DATA chunks
pending receipt; primary path; most recent SRTT on primary path;
RTO on primary path; SRTT and RTO on other destination addresses.

COMMUNICATION UP notification: "Potentially
Failed" (PF) paths. When a lost communication to an
endpoint path is restored or when in PF state, SCTP becomes ready to send or receive
user messages, this notification informs the application process
about the affected association, the type of event will not
entirely give up sending on that has
occurred, the complete set of sockets of the peer, path, but it will preferably send
data on other active paths if such paths are available. Entering
the PF state is done upon exceeding a configured maximum number of allowed streams and the inbound stream count (the number
of streams the peer endpoint has requested).

DATA ARRIVE notification: When
retransmissions. Thus, for all paths where this mechanism is
used, there are two configurable error thresholds: one to decide
that a message path is ready in PF state, and one to be retrieved
via the Receive primitive, decide that the application transport
address is informed by this
notification.

SEND FAILURE notification / Receive Unsent Message unreachable.

Set / Receive
Unacknowledged Message: When a message cannot be delivered via Get Authentication Parameters: This allows an
association, endpoint to add/
remove key material to/from an association. In addition, the sender
chunk types being authenticated can be informed about it and learn whether queried. This is provided
by the message has just not been acknowledged or (e.g. protocol extension defined in case of
lifetime expiry) if it has not even been sent.

NETWORK STATUS CHANGE notification: The NETWORK STATUS CHANGE
notification informs the application about a socket becoming
active/inactive.

COMMUNICATION LOST notification: When SCTP loses communication to [RFC4895].

Add / Reset Streams, Reset Association: This allows an endpoint (e.g. via Heartbeats to
add streams to an existing association or excessive retransmission) or
detects an abort, this notification informs to reset them
individually. Additionally, the application
process of association can be reset. This
is provided by the affected protocol extension defined in [RFC6525].

Status: The 'Status' primitive returns a data block with information
about a specified association, containing: association connection
state; destination transport address list; destination transport
address reachability states; current local and the type peer receiver
window sizes; current local congestion window sizes; number of event (failure
OR termination in response
unacknowledged DATA chunks; number of DATA chunks pending receipt;
primary path; most recent SRTT on primary path; RTO on primary
path; SRTT and RTO on other destination addresses [RFC4960] and
MTU per path [RFC6458].

Enable / Disable Interleaving: This allows to a shutdown enable or abort request).

SHUTDOWN COMPLETE notification: When SCTP completes the shutdown
procedures, this notification is passed to disable the upper layer,
informing
negotiation of user message interleaving support for future
associations. For existing associations it about the affected assocation.

AUTHENICATION notification: When SCTP wants is possible to notify the upper
layer regarding the key management related query
whether user message interleaving support was negotiated or not on
a particular association [I-D.ietf-tsvwg-sctp-ndata].

Set Stream Scheduler: This allows to the extension
defined in [RFC4895], this notification select a stream scheduler per
association, with a choice of: First Come First Serve, Round
Robin, Round Robin per Packet, Priority Based, Fair Bandwidth,
Weighted Fair Queuing. How these schedulers operate is passed described
in detail in [I-D.ietf-tsvwg-sctp-ndata].

Configure Stream Scheduler: This allows to change a parameter per
stream for the upper
layer.

ADAPTATION LAYER INDICATION notification: When SCTP completes schedulers: a priority value for the
association setup Priority Based
scheduler and a weight for the peer provided Weighted Fair Queuing scheduler.

Enable/disable NODELAY: This turns on/off any Nagle-like algorithm
for an adaptation layer
indication, this is passed to the upper layer. association [RFC6458].

Configure send buffer size: This extension is
defined in [RFC5061] and [RFC6458].

STREAM RESET notification: When SCTP completes controls the procedure for
resetting streams as specified amount of data SCTP
may have waiting in [RFC6525], this notification is
passed internal buffers to be sent or retransmitted
[RFC6458].

Configure receive buffer size: This sets the upper layer, informing it about receive buffer size in
octets, thereby controlling the result.

ASSOCIATION RESET notification: When receiver window for an association
[RFC6458].

Configure message fragmentation: If a user message causes an SCTP completes
packet to exceed the association
reset procedure as specified in [RFC6525], this notification maximum fragmentation size (which can be
provided by the application, and is
passed to otherwise the upper layer, informing PMTU size), then
the message will be fragmented by SCTP. Disabling message
fragmentation will produce an error instead of fragmenting the
message [RFC6458].

Configure Path MTU Discovery: Section 8.1.12 of [RFC6458] explains
how Path MTU Discovery can be enabled or disabled per peer address
of an association. When it about is enabled, the result.

STREAM CHANGE notification: current Path MTU value
can be obtained. When SCTP completes it is disabled, the procedure used Path MTU to increase be used can
be controlled by the application.

Configure delayed SACK timer: The time before sending a SACK can be
adjusted; delaying SACKs can be disabled; the number of streams packets
that must be received before a SACK is sent without waiting for
the delay timer to expire can be configured [RFC6458].

Set Cookie life value: The Cookie life value can be adjusted as specified
explained in [RFC6525], this
notification Section 8.1.2 of [RFC6458]. "Valid.Cookie.Life" is passed to the upper layer, informing it about
also one of the
result.

3.3.1. Excluded Primitives or Parameters parameters listed as potentially adjustable with
SETPROTOCOLPARAMETERS in [RFC4960].

Set maximum burst: The 'Receive' primitive maximum burst of packets that can return certain additional information,
but this is be emitted
by a particular association (default 4, and values above 4 are
optional to implement and therefore not considered. With
a COMMUNICATION LOST notification, some more information may
optionally be passed to the application (e.g., identification to
retrieve unsent and unacknowledged data). SCTP "can invoke" a
COMMUNICATION ERROR notification and "may send" a RESTART
notification, making these two notifications optional to implement.
The list provided under 'Status' includes "etc", indicating that more
information could implement) can be provided. The primitive 'Get SRTT Report'
returns information that is included adjusted as explained in the information that 'Status'
provides and Section
8.1.2 of [RFC6458]. "Max.Burst" is therefore not discussed. Similarly, 'Set Failure
Threshold' sets only also one out of various possible parameters included
in 'Set Protocol Parameters'. The 'Destroy SCTP Instance' API
function was excluded: it erases the SCTP instance that was created
by 'Initialize', but is not a Primitive parameters
listed as defined potentially adjustable with SETPROTOCOLPARAMETERS in this document
because it does not relate to a Transport Service Feature.

3.4. Primitives Provided by UDP and UDP-Lite

The primitives provided by UDP
[RFC4960].

Configure RTO calculation: [RFC4960] lists the following adjustable
parameters: RTO.Initial; RTO.Min; RTO.Max; RTO.Alpha; RTO.Beta.
Only the initial, minimum and UDP-Lite maximum RTO are also described in [FJ16].

4. Pass 2 as
configurable [RFC6458].

Set DSCP value: Section 8.1.12 of [RFC6458] explains how to set the
DSCP value per peer address of an association.

Set IPv6 flow label: Section 8.1.12 of [RFC6458] explains how to set
the flow label field per peer address of an association.

Set Partial Delivery Point: This pass categorizes allows to specify the primitives from pass 1 based on whether
they relate size of a
message where partial delivery will be invoked. Setting this to a connection
lower value will cause partial deliveries to happen more often
[RFC6458].

COMMUNICATION UP notification: When a lost communication to an
endpoint is restored or when SCTP becomes ready to data transmission. Primitives are
presented following the nomenclature
"CATEGORY.[SUBCATEGORY].PRIMITIVENAME.PROTOCOL". The CATEGORY can be
CONNECTION send or DATA. Within receive
user messages, this notification informs the CONNECTION category, ESTABLISHMENT,
AVAILABILITY, MAINTENANCE application process
about the affected association, the type of event that has
occurred, the complete set of sockets of the peer, the maximum
number of allowed streams and TERMINATION subcategories the inbound stream count (the number
of streams the peer endpoint has requested). If interleaving is
supported by both endpoints, this information is also included in
this notification.

RESTART notification: When SCTP has detected that the peer has
restarted, this notification is passed to the upper layer
[RFC6458].

DATA ARRIVE notification: When a message is ready to be retrieved
via the Receive primitive, the application is informed by this
notification.

SEND FAILURE notification / Receive Unsent Message / Receive
Unacknowledged Message: When a message cannot be delivered via an
association, the sender can be
considered. The DATA category does informed about it and learn whether
the message has just not have any SUBCATEGORY (as been acknowledged or (e.g. in case of
lifetime expiry) if it has not even been sent. This can also
inform the sender that a part of
now). the message has been successfully
delivered.

NETWORK STATUS CHANGE notification: The PROTOCOL name "UDP(-Lite)" is used when primitives are
equivalent for UDP and UDP-Lite; NETWORK STATUS CHANGE
notification informs the PROTOCOL name "TCP" refers application about a socket becoming
active/inactive [RFC4960] or "Potentially Failed" [RFC7829].

COMMUNICATION LOST notification: When SCTP loses communication to an
endpoint (e.g. via Heartbeats or excessive retransmission) or
detects an abort, this notification informs the application
process of the affected association and the type of event (failure
OR termination in response to a shutdown or abort request).

SHUTDOWN COMPLETE notification: When SCTP completes the shutdown
procedures, this notification is passed to the upper layer,
informing it about the affected assocation.

AUTHENTICATION notification: When SCTP wants to notify the upper
layer regarding the key management related to the extension
defined in [RFC4895], this notification is passed to the upper
layer.

ADAPTATION LAYER INDICATION notification: When SCTP completes the
association setup and the peer provided an adaptation layer
indication, this is passed to the upper layer. This extension is
defined in [RFC5061] and [RFC6458].

STREAM RESET notification: When SCTP completes the procedure for
resetting streams as specified in [RFC6525], this notification is
passed to the upper layer, informing it about the result.

ASSOCIATION RESET notification: When SCTP completes the association
reset procedure as specified in [RFC6525], this notification is
passed to the upper layer, informing it about the result.

STREAM CHANGE notification: When SCTP completes the procedure used
to increase the number of streams as specified in [RFC6525], this
notification is passed to the upper layer, informing it about the
result.

SENDER DRY notification: When SCTP has no more user data to send or
retransmit on a particular association, this notification is
passed to the upper layer [RFC6458].

PARTIAL DELIVERY ABORTED notification: When a receiver has begun to
receive parts of a user message but the delivery of this message
is then aborted, this notification is passed to the upper layer
(section 6.1.7 of [RFC6458]).

3.3.1. Excluded Primitives or Parameters

The 'Receive' primitive can return certain additional information,
but this is optional to implement and therefore not considered. With
a COMMUNICATION LOST notification, some more information may
optionally be passed to the application (e.g., identification to
retrieve unsent and unacknowledged data). SCTP "can invoke" a
COMMUNICATION ERROR notification and "may send" a RESTART
notification, making these two notifications optional to implement.
The list provided under 'Status' includes "etc", indicating that more
information could be provided. The primitive 'Get SRTT Report'
returns information that is included in the information that 'Status'
provides and is therefore not discussed. The 'Destroy SCTP Instance'
API function was excluded: it erases the SCTP instance that was
created by 'Initialize', but is not a Primitive as defined in this
document because it does not relate to a Transport Feature. The
SHUTDOWN EVENT described in Section 6.1 of [RFC6458] informs an
application that the peer has sent a SHUTDOWN, and hence no further
data should be sent on this socket. However, if an application would
try to send data on the socket, it would get an error message anyway;
thus, this event is classified as "just affecting the application
programming style, not how the underlying protocol operates" and not
included here.

3.4. Primitives Provided by UDP and UDP-Lite

The primitives provided by UDP and UDP-Lite are described in [FJ16].

3.5. The service of LEDBAT

The service of the Low Extra Delay Background Transport (LEDBAT)
congestion control mechanism is described in the abstract of
[RFC6817] as follows: "LEDBAT is designed for use by background bulk-
transfer applications to be no more aggressive than standard TCP
congestion control (as specified in RFC 5681) and to yield in the
presence of competing flows, thus limiting interference with the
network performance of competing flows."
LEDBAT does not have any primitives, as LEDBAT is not a transport
protocol. [RFC6817] states: "LEDBAT can be used as part of a
transport protocol or as part of an application, as long as the data
transmission mechanisms are capable of carrying timestamps and
acknowledging data frequently. LEDBAT can be used with TCP, Stream
Control Transmission Protocol (SCTP), and Datagram Congestion Control
Protocol (DCCP), with appropriate extensions where necessary; and it
can be used with proprietary application protocols, such as those
built on top of UDP for peer-to- peer (P2P) applications." At the
time of writing, the appropriate extensions for TCP, SCTP or DCCP do
not exist.

A numer of configurable parameters exist in the LEDBAT specification:
TARGET, which is the queuing delay target at which LEDBAT tries to
operate, must be set to 100ms or less. ALLOWED_INCREASE (should be
1, must be greater than 0) limits the speed at which LEDBAT increases
its rate. GAIN, which MUST be set to 1 or less to avoid a faster
ramp-up than TCP Reno, determines how quickly the sender responds to
changes in queueing delay. Implementations may divide GAIN into two
parameters, one for increase and a possibly larger one for decrease.
We call these parameters GAIN_INC and GAIN_DEC here. BASE_HISTORY is
the size of the list of measured base delays, and SHOULD be 10. This
list can be filtered using a FILTER() function which is not
prescribed in [RFC6817], yielding a list of size CURRENT_FILTER. The
initial and minimum congestion windows, INIT_CWND and MIN_CWND,
should both be 2.

Regarding which of these parameters should be under control of an
application, the possible range goes from exposing nothing on the one
hand, to considering everything that is not fully prescribed with a
MUST in [RFC6817] as a parameter on the other hand. Function
implementations are not provided as a parameter to any of the
transport protocols discussed here, and hence we do not regard the
FILTER() function as a parameter. However, to avoid unnecessarily
limiting future implementations, we consider all other parameters
above as tunable parameters that a TAPS system should expose.

4. Pass 2

This pass categorizes the primitives from pass 1 based on whether
they relate to a connection or to data transmission. Primitives are
presented following the nomenclature
"CATEGORY.[SUBCATEGORY].PRIMITIVENAME.PROTOCOL". The CATEGORY can be
CONNECTION or DATA. Within the CONNECTION category, ESTABLISHMENT,
AVAILABILITY, MAINTENANCE and TERMINATION subcategories can be
considered. The DATA category does not have any SUBCATEGORY. The
PROTOCOL name "UDP(-Lite)" is used when primitives are equivalent for
UDP and UDP-Lite; the PROTOCOL name "TCP" refers to both TCP and
MPTCP. We present "connection" as a general protocol-independent
concept and use it to refer to, e.g., TCP connections (identifiable
by a unique pair of IP addresses and TCP port numbers), SCTP
associations (identifiable by multiple IP address and port number
pairs), as well UDP and UDP-Lite connections (identifiable by a
unique socket pair).

Some minor details are omitted for the sake of generalization --
e.g., SCTP's 'close' [RFC4960] returns success or failure, and lets
the application control whether further receive or send operations or
both are disabled [RFC6458]. This is not described in the same way
for TCP in [RFC0793], but these details play no significant role for
the primitives provided by either TCP or SCTP (for the sake of being
generic, it could be assumed that both receive and send operations
are disabled in both cases).

The TCP 'send' and 'receive' primitives include usage of an "URGENT"
mechanism. This mechanism is required to implement the "synch
signal" used by telnet [RFC0854], but SHOULD NOT be used by new
applications [RFC6093]. Because pass 2 is meant as a basis for the
creation of TAPS systems, the "URGENT" mechanism is excluded. This
also concerns the notification "Urgent pointer advance" in the
ERROR_REPORT described in Section 4.2.4.1 of [RFC1122].

Since LEDBAT is a congestion control mechanism and not a protocol, it
is not currently defined when to enable / disable or configure the
mechanism. For instance, it could be a one-time choice upon
connection establishment or when listening for incoming connections,
in which case it should be categorized under CONNECTION.ESTABLISHMENT
or CONNECTION.AVAILABILITY, respectively. To avoid unnecessarily
limiting future implementations, it was decided to place it under
CONNECTION.MAINTENANCE, with all parameters that are described in
[RFC6817] made configurable.

4.1. CONNECTION Related Primitives

ESTABLISHMENT:
Active creation of a connection from one transport endpoint to one or
more transport endpoints.
Interfaces to UDP and UDP-Lite allow both connection-oriented and
connection-less usage of the API . [RFC8085]

o CONNECT.TCP:
Pass 1 primitive / event: 'open' (active) or 'open' (passive) with
socket, followed by 'send'
Parameters: 1 local IP address (optional); 1 destination transport
address (for active open; else the socket and the local IP address
of the succeeding incoming connection request will be maintained);
timeout (optional); options (optional); user message (optional)
Comments: If the local IP address is not provided, a default
choice will automatically be made. The timeout can also be a
retransmission count. The options are IP options to be used on
all segments of the connection. At least the Source Route option
is mandatory for TCP to provide. The user message may be
transmitted to the peer application immediately upon reception of
the TCP SYN packet. To benefit from the lower latency this
provides as part of the experimental TFO mechanism, its length
must be at most the TCP's maximum segment size (minus TCP options
used in the SYN). The message may also be delivered more than
once to the application on the remote host.

o CONNECT.SCTP:
Pass 1 primitive / event: 'initialize', followed by 'enable /
disable interleaving' (optional), followed by 'associate'
Parameters: list of local SCTP port number / IP address pairs
(initialize); one or several sockets (identifying the peer);
outbound stream count; maximum allowed inbound stream count;
adaptation layer indication (optional); chunk types required to be
authenticated (optional); request interleaving on/off; maximum
number of INIT attemps (optional); maximum init. RTO for INIT
(optional); user message (optional); remote UDP port number
(optional)
Returns: socket list or failure
Comments: 'initialize' needs to be called only once per list of
local SCTP port number / IP address pairs. One socket will
automatically be chosen; it can later be changed in MAINTENANCE.
The user message may be transmitted to the peer application
immediately upon reception of the packet containing the COOKIE-
ECHO chunk. To benefit from the lower latency this provides, its
length must be limited such that it fits into the packet
containing the COOKIE-ECHO chunk. If a remote UDP port number is
provided, SCTP packets will be encapsulated in UDP.

o CONNECT.MPTCP:
This is similar to CONNECT.TCP except for one additional boolean
parameter that allows to enable or disable MPTCP for a particular
connection or socket (default: enabled).

o CONNECT.UDP(-Lite):
Pass 1 primitive / event: 'connect' followed by 'send'.
Parameters: 1 local IP address (default (ANY), or specified); 1
destination transport address; 1 local port (default (OS chooses),
or specified); 1 destination port (default (OS chooses), or
specified).
Comments: Associates a transport address creating a UDP(-Lite)
socket connection. This can be called again with a new transport
address to create a new connection. The CONNECT function allows
an application to receive errors from messages sent to a transport
address.

AVAILABILITY:
Preparing to receive incoming connection requests.

o LISTEN.TCP:
Pass 1 primitive / event: 'open' (passive)
Parameters: 1 local IP address (optional); 1 socket (optional);
timeout (optional); buffer to receive a user message (optional)
Comments: if the socket and/or local IP address is provided, this
waits for incoming connections from only and/or to only the
provided address. Else this waits for incoming connections
without this / these constraint(s). ESTABLISHMENT can later be
performed with 'send'. If a buffer is provided to receive a user
message, a user message can be received from a TFO-enabled sender
before TCP's connection handshake is completed. This message may
arrive multiple times.

o LISTEN.SCTP:
Pass 1 primitive / event: 'initialize', followed by 'COMMUNICATION
UP' or 'RESTART' notification and possibly 'ADAPTATION LAYER'
notification
Parameters: list of local SCTP port number / IP address pairs
(initialize)
Returns: socket list; outbound stream count; inbound stream count;
adaptation layer indication; chunks required to be authenticated;
interleaving supported on both TCP and MPTCP. We present "connection" as a general protocol-
independent concept and use it sides yes/no
Comments: initialize needs to refer to, e.g., TCP connections
(identifiable by a unique pair be called only once per list of IP addresses and TCP port numbers),
local SCTP associations (identifiable by multiple IP address and port number pairs), as well UDP and UDP-Lite connections (identifiable by / IP address pairs. COMMUNICATION UP can
also follow a unique socket pair).

Some minor details are omitted for COMMUNICATION LOST notification, indicating that the sake of generalization --
e.g., SCTP's 'close' [RFC4960] returns success or failure, whereas
this
lost communication is not described in restored. If the same way peer has provided an
adaptation layer indication, an 'ADAPTATION LAYER' notification is
issued.

o LISTEN.MPTCP:
This is similar to LISTEN.TCP except for TCP in [RFC0793], but this
detail plays no significant role one additional boolean
parameter that allows to enable or disable MPTCP for the primitives provided by
either TCP a particular
connection or SCTP. socket (default: enabled).

o LISTEN.UDP(-Lite):
Pass 1 primitive / event: 'receive'.
Parameters: 1 local IP address (default (ANY), or specified); 1
destination transport address; local port (default (OS chooses),
or specified); destination port (default (OS chooses), or
specified).
Comments: The TCP 'send' and 'receive' primitives include usage of receive function registers the application to listen
for incoming UDP(-Lite) datagrams at an "URGENT"
mechanism. This mechanism is required endpoint.

MAINTENANCE:
Adjustments made to an open connection, or notifications about it.
These are out-of-band messages to implement the "synch
signal" used by telnet [RFC0854], but SHOULD NOT protocol that can be used by new
applications [RFC6093]. Because pass 2 is meant as issued at
any time, at least after a basis connection has been established and before
it has been terminated (with one exception: CHANGE_TIMEOUT.TCP can
only be issued for the
creation of TAPS systems, the "URGENT" mechanism an open connection when DATA.SEND.TCP is excluded. This called).
In some cases, these primitives can also concerns the notification "Urgent pointer advance" in be immediately issued during
ESTABLISHMENT or AVAILABILITY, without waiting for the
ERROR_REPORT described in Section 4.2.4.1 of [RFC1122].

4.1. CONNECTION Related Primitives

ESTABLISHMENT:
Active creation of a connection from one transport endpoint to one or
more transport endpoints.
Interfaces to
be opened (e.g. CHANGE_TIMEOUT.TCP can be done using TCP's 'open'
primitive). For UDP and UDP-Lite allow both connection-oriented and
connection-less usage of the API [I-D.ietf-tsvwg-rfc5405bis] UDP-Lite, these functions may establish a
setting per connection, but may also be changed per datagram message.

o CONNECT.TCP: CHANGE_TIMEOUT.TCP:
Pass 1 primitive / event: 'open' (active) or 'open' (passive) with
socket, followed by 'send' combined with
unspecified control of per-connection state variables
Parameters: 1 local IP address timeout value (optional); 1 destination transport
address (for active open; else the socket and ADV_UTO (optional); boolean
UTO_ENABLED (optional, default false); boolean CHANGEABLE
(optional, default true)
Comments: when sending data, an application can adjust the local IP address
of
connection's timeout value (time after which the succeeding incoming connection request will
be maintained);
timeout (optional); options (optional)
Comments: aborted if data could not be delivered). If the local IP address UTO_ENABLED is not
true, the user timeout value (or, if provided, a default
choice the value ADV_UTO)
will automatically be made. The advertised for the TCP on the other side of the connection
to adapt its own user timeout can also be accordingly. UTO_ENABLED controls
whether the UTO option is enabled for a
retransmission count. The options are IP options connection. This applies
to both sending and receiving. CHANGEABLE controls whether the
user timeout may be used changed based on
all segments of a UTO option received from
the connection. At least other end of the Source Route option connection; it becomes false when 'timeout
value' is mandatory for TCP to provide. used.

o CONNECT.SCTP: CHANGE_TIMEOUT.SCTP:
Pass 1 primitive / event: 'initialize', followed by 'associate' 'Change HeartBeat' combined with
'Configure Max. Retransmissions of an Association'
Parameters: list 'Change HeartBeat': heartbeat frequency; 'Configure
Max. Retransmissions of local SCTP port number / IP address pairs
(initialize); 1 socket; outbound stream count; adaptation layer
indication; chunk types required to be authenticated
Returns: socket list an Association': Association.Max.Retrans
Comments: 'initialize' needs to be called only once per list of
local SCTP port number Change Heartbeat can enable / IP address pairs. One socket disable heartbeats in SCTP
as well as change their frequency. The parameter
Association.Max.Retrans defines after how many unsuccessful
transmissions of any packets (including heartbeats) the
association will
automatically be chosen; it terminated; thus these two primitives /
parameters together can later be changed in MAINTENANCE.

o CONNECT.MPTCP:
This is yield a similar to CONNECT.TCP except behavior for one additional boolean
parameter that allows to enable or disable MPTCP SCTP
associations as CHANGE_TIMEOUT.TCP does for a particular
connection or socket (default: enabled). TCP connections.

o CONNECT.UDP(-Lite): DISABLE_NAGLE.TCP:
Pass 1 primitive / event: 'connect' followed by 'send'. not specified
Parameters: 1 local IP address (default (ANY), or specified); 1
destination transport address; 1 local port (default (OS chooses),
or specified); 1 destination port (default (OS chooses), or
specified). one boolean value
Comments: Associates a transport address creating a UDP(-Lite)
socket connection. This can be called again with a new transport
address the Nagle algorithm delays data transmission to create increase
the chance to send a new connection. The CONNECT function allows
an full-sized segment. An application must be
able to receive errors from messages sent to disable this algorithm for a transport
address.

AVAILABILITY:
Preparing to receive incoming connection requests. connection.

o LISTEN.TCP: DISABLE_NAGLE.SCTP:
Pass 1 primitive / event: 'open' (passive) 'Enable/disable NODELAY'
Parameters: 1 local IP address (optional); 1 socket (optional);
timeout (optional) one boolean value
Comments: if the socket and/or local IP address is provided, this
waits for incoming connections from only and/or Nagle-like algorithms delay data transmission to only
increase the
provided address. Else this waits for incoming connections
without this chance to send a full-sized packet.

o REQUEST_HEARTBEAT.SCTP:
Pass 1 primitive / these constraint(s). ESTABLISHMENT can later be
performed with 'send'. event: 'Request HeartBeat'
Parameters: socket
Returns: success or failure
Comments: requests an immediate heartbeat on a path, returning
success or failure.

o LISTEN.SCTP: ADD_PATH.MPTCP:
Pass 1 primitive / event: 'initialize', followed by 'COMMUNICATION
UP' notification and possibly 'ADAPTATION LAYER' notification not specified
Parameters: list of local SCTP port number / IP address pairs
(initialize)
Returns: socket list; outbound stream count; inbound stream count;
adaptation layer indication; chunks required to be authenticated
Comments: initialize needs to be called only once per list of and optionally the local SCTP port number / IP address pairs. COMMUNICATION UP can
also follow a COMMUNICATION LOST notification, indicating that
Comments: the
lost communication is restored. If application specifies the peer has provided an
adaptation layer indication, an 'ADAPTATION LAYER' notification is
issued.

o LISTEN.MPTCP:
This is similar to LISTEN.TCP except for one additional boolean
parameter local IP address and port
number that allows to enable or disable MPTCP for a particular
connection or socket (default: enabled). must be used for a new subflow.

o LISTEN.UDP(-Lite): ADD_PATH.SCTP:
Pass 1 primitive / event: 'receive'. Change Local Address / Set Peer Primary
Parameters: 1 local IP address (default (ANY), or specified);

o REM_PATH.MPTCP:
Pass 1
destination transport address; primitive / event: not specified
Parameters: local IP address, local port (default (OS chooses),
or specified); destination number, remote IP
address, remote port (default (OS chooses), or
specified). number
Comments: The receive function registers the application to listen
for incoming UDP(-Lite) datagrams at an endpoint.

MAINTENANCE:
Adjustments made to an open connection, or notifications about it.
These are out-of-band messages to removes the protocol that can be issued at
any time, at least after subflow specified by the IP/
port-pair. The MPTCP implementation must trigger a connection has been established and before
it has been terminated (with one exception: CHANGE-TIMEOUT.TCP can
only removal of the
subflow that belongs to this IP/port-pair.

o REM_PATH.SCTP:
Pass 1 primitive / event: 'Change Local Address / Set Peer
Primary'
Parameters: local IP address

o SET_PRIMARY.SCTP:
Pass 1 primitive / event: 'Set Primary'
Parameters: socket
Returns: result of attempting this operation
Comments: update the current primary address to be issued for an open connection when DATA.SEND.TCP used, based on
the set of available sockets of the association.

o SET_PEER_PRIMARY.SCTP:
Pass 1 primitive / event: 'Change Local Address / Set Peer
Primary'
Parameters: local IP address
Comments: this is called).
In some cases, these primitives can also be immediately issued during
ESTABLISHMENT or AVAILABILITY, without waiting only advisory for the connection to
be opened (e.g. CHANGE-TIMEOUT.TCP can be done using TCP's 'open'
primitive). For UDP and UDP-Lite, these functions may establish a
setting per connection, but may also be changed per datagram message. peer.

o CHANGE-TIMEOUT.TCP: CONFIG_SWITCHOVER.SCTP:
Pass 1 primitive / event: 'open' or 'send' combined with
unspecified control of per-connection state variables 'Configure Path Switchover'
Parameters: timeout value (optional); ADV_UTO (optional); boolean
UTO_ENABLED (optional, default false); boolean CHANGEABLE
(optional, default true)
Comments: when sending data, an application can adjust the
connection's timeout value (time primary max retrans (no. of retransmissions after
which the connection will
be aborted if data could not be delivered). If UTO_ENABLED a path is
true, the user timeout value (or, if provided, the value ADV_UTO)
will be advertised for the TCP on the other side considered inactive), PF max retrans (no. of the connection
to adapt its own user timeout accordingly. UTO_ENABLED controls
whether the UTO option is enabled for
retransmissions after which a connection. This applies path is considered to both sending be
"Potentially Failed", and receiving. CHANGEABLE controls whether the
user timeout may others will be changed based on a UTO option received from
the other end of the connection; it becomes false when 'timeout
value' is used. preferably used)
(optional)

o CHANGE-TIMEOUT.SCTP: STATUS.SCTP:
Pass 1 primitive / event: 'Change HeartBeat' combined 'Status', 'Enable / Disable
Interleaving' and 'NETWORK STATUS CHANGE notification'.
Returns: data block with 'Set
Protocol Parameters'
Parameters: 'Change HeartBeat': heartbeat frequency; 'Set Protocol
Parameters': Association.Max.Retrans (whole association) or
Path.Max.Retrans (per socket) information about a specified
association, containing: association connection state; destination
transport address list; destination transport address reachability
states; current local and peer receiver window sizes; current
local congestion window sizes; number of unacknowledged DATA
chunks; number of DATA chunks pending receipt; primary path; most
recent SRTT on primary path; RTO on primary path; SRTT and RTO on
other destination addresses; MTU per path; interleaving supported
yes/no.
Comments: Change Heartbeat can enable The NETWORK STATUS CHANGE notification informs the
application about a socket becoming active/inactive; this only
affects the programming style, as the same information is also
available via 'Status'.

o STATUS.MPTCP:
Pass 1 primitive / disable heartbeats in SCTP
as well as change their frequency. event: not specified
Returns: list of pairs of tuples of IP address and TCP port number
of each subflow. The parameter
Association.Max.Retrans defines after how many unsuccessful
heartbeats first of the connection will be terminated; thus these two
primitives / parameters together can yield a similar behavior to
CHANGE-TIMEOUT.TCP. pair is the local IP and port
number, while the second is the remote IP and port number.

o DISABLE-NAGLE.TCP: SET_DSCP.TCP:
Pass 1 primitive / event: not specified
Parameters: one boolean DSCP value
Comments: the Nagle algorithm delays data transmission to increase
the chance to send a full-sized segment. An this allows an application must be
able to disable change the DSCP value for
outgoing segments. For TCP this algorithm was originally specified for a connection. the
TOS field [RFC1122], which is here interpreted to refer to the
DSField [RFC3260].

o REQUESTHEARTBEAT.SCTP: SET_DSCP.SCTP:
Pass 1 primitive / event: 'Request HeartBeat' 'Set DSCP value'
Parameters: socket
Returns: success or failure DSCP value
Comments: requests this allows an immediate heartbeat application to change the DSCP value for
outgoing packets on a path, returning
success or failure. path.

o SETPROTOCOLPARAMETERS.SCTP: SET_DSCP.UDP(-Lite):
Pass 1 primitive / event: 'Set Protocol Parameters'
Parameters: RTO.Initial; RTO.Min; RTO.Max; Max.Burst; RTO.Alpha;
RTO.Beta; Valid.Cookie.Life; Association.Max.Retrans;
Path.Max.Retrans; Max.Init.Retransmits; HB.interval; HB.Max.Burst;
PotentiallyFailed.Max.Retrans; Primary.Switchover.Max.Retrans;
Remote.UDPEncapsPort. 'SET_DSCP'
Parameter: DSCP value
Comments: This allows an application to change the DSCP value for
outgoing UDP(-Lite) datagrams. [RFC7657] and [RFC8085] provide
current guidance on using this value with UDP.

o SETPRIMARY.SCTP: ERROR.TCP:
Pass 1 primitive / event: 'Set Primary'
Parameters: socket 'ERROR_REPORT'
Returns: result of attempting this operation reason (encoding not specified); subreason (encoding not
specified)
Comments: update the current primary address to soft errors that can be used, based on
the set of available sockets of the association. ignored without harm by many
applications; an application should be able to disable these
notifications. The reported conditions include at least: ICMP
error message arrived; Excessive Retransmissions.

o SETPEERPRIMARY.SCTP: ERROR.UDP(-Lite):
Pass 1 primitive / event: Change Local Address / Set Peer Primary
Parameters: local IP address 'ERROR_REPORT'.
Returns: Error report
Comments: this is only advisory for the peer. This returns soft errors that may be ignored without
harm by many applications; An application must connect to be able
receive these notifications.

o SETAUTH.SCTP: SET_AUTH.SCTP:
Pass 1 primitive / event: Set 'Set / Get Authentication Parameters Parameters'
Parameters: key_id, key, hmac_id

o GETAUTH.SCTP: GET_AUTH.SCTP:
Pass 1 primitive / event: Set 'Set / Get Authentication Parameters Parameters'
Parameters: key_id, chunk_list

o RESETSTREAM.SCTP: RESET_STREAM.SCTP:
Pass 1 primitive / event: Add 'Add / Reset Streams, Reset Association Association'
Parameters: sid, direction

o RESETSTREAM-EVENT.SCTP: RESET_STREAM-EVENT.SCTP:
Pass 1 primitive / event: STREAM 'STREAM RESET notification notification'
Parameters: information about the result of RESETSTREAM.SCTP. RESET_STREAM.SCTP.
Comments: This is issued when the procedure for resetting streams
has completed.

o RESETASSOC.SCTP: RESET_ASSOC.SCTP:
Pass 1 primitive / event: Add 'Add / Reset Streams, Reset Association Association'
Parameters: information related to the extension defined in
[RFC3260].

o RESETASSOC-EVENT.SCTP: RESET_ASSOC-EVENT.SCTP:
Pass 1 primitive / event: ASSOCIATION 'ASSOCIATION RESET notification notification'
Parameters: information about the result of RESETASSOC.SCTP. RESET_ASSOC.SCTP.
Comments: This is issued when the procedure for resetting an
association has completed.

o ADDSTREAM.SCTP: ADD_STREAM.SCTP:
Pass 1 primitive / event: Add 'Add / Reset Streams, Reset Association Association'
Parameters: number if outgoing and incoming streams to be added

o ADDSTREAM-EVENT.SCTP: ADD_STREAM-EVENT.SCTP:
Pass 1 primitive / event: STREAM 'STREAM CHANGE notification notification'
Parameters: information about the result of ADDSTREAM.SCTP.

Comments: This is issued when the procedure for adding a stream
has completed.

o ERROR.TCP:
Pass 1 primitive / event: 'ERROR_REPORT'
Returns: reason (encoding not specified); subreason (encoding not
specified)
Comments: soft errors that can be ignored without harm by many
applications; an application should be able to disable these
notifications. The reported conditions include at least: ICMP
error message arrived; Excessive Retransmissions.

o ERROR.UDP(-Lite):
Pass 1 primitive / event: 'ERROR_REPORT'.
Returns: Error report
Comments: This returns soft errors that may be ignored without
harm by many applications; An application must connect to be able
receive these notifications.

o STATUS.SCTP:
Pass 1 primitive / event: 'Status' and 'NETWORK STATUS CHANGE'
notification
Returns: data block with information about a specified
association, containing: association connection state; socket
list; destination transport address reachability states; current
receiver window size; current congestion window sizes; number of
unacknowledged DATA chunks; number of DATA chunks pending receipt;
primary path; most recent SRTT on primary path; RTO on primary
path; SRTT and RTO on other destination addresses. The NETWORK
STATUS CHANGE notification informs ADD_STREAM.SCTP.
Comments: This is issued when the application about procedure for adding a socket
becoming active/inactive. stream
has completed.

o STATUS.MPTCP: SET_STREAM_SCHEDULER.SCTP:
Pass 1 primitive / event: not specified
Returns: list of pairs of tuples of IP address and TCP port number
of each subflow. The first 'Set Stream Scheduler'
Parameters: scheduler identifier
Comments: choice of First Come First Serve, Round Robin, Round
Robin per Packet, Priority Based, Fair Bandwidth, Weighted Fair
Queuing.

o CONFIGURE_STREAM_SCHEDULER.SCTP:
Pass 1 primitive / event: 'Configure Stream Scheduler'
Parameters: priority
Comments: the pair priority value only applies when Priority Based or
Weighted Fair Queuing scheduling is chosen with
SET_STREAM_SCHEDULER.SCTP. The meaning of the local IP and port
number, while the second parameter differs
between these two schedulers but in both cases it realizes some
form of prioritization regarding how bandwidth is the remote IP and port number. divided among
streams.

o SET_DSCP.TCP: SET_FLOWLABEL.SCTP:
Pass 1 primitive / event: not specified 'Set IPv6 flow label'
Parameters: DSCP value flow label
Comments: this allows an application to change the DSCP value IPv6 header's
flow label field for outgoing segments. For TCP packets on a path.

o AUTHENTICATION_NOTIFICATION-EVENT.SCTP:
Pass 1 primitive / event: 'AUTHENTICATION notification'
Returns: information regarding key management.

o CONFIG_SEND_BUFFER.SCTP:
Pass 1 primitive / event: 'Configure send buffer size'
Parameters: size value in octets

o CONFIG_RECEIVE_BUFFER.SCTP:
Pass 1 primitive / event: 'Configure receive buffer size'
Parameters: size value in octets
Comments: this was originally specified for controls the
TOS field [RFC1122], which receiver window.

o CONFIG_FRAGMENTATION.SCTP:
Pass 1 primitive / event: 'Configure message fragmentation'
Parameters: one boolean value (enable/disable), maximum
fragmentation size (optional; default: PMTU)
Comments: if fragmentation is here interpreted to refer enabled, messages exceeding the
maximum fragmentation size will be fragmented. If fragmentation
is disabled, trying to send a message that exceeds the
DSField [RFC3260]. maximum
fragmentation size will produce an error.

o SET_DSCP.UDP(-Lite): CONFIG_PMTUD.SCTP:
Pass 1 primitive / event: 'SET_DSCP'
Parameter: DSCP 'Configure Path MTU Discovery'
Parameters: one boolean value (PMTUD on/off), PMTU value
(optional)
Returns: PMTU value
Comments: This allows an application to change the DSCP returns a meaningful PMTU value for
outgoing UDP(-Lite) datagrams. [RFC7657] when PMTUD is
enabled (the boolean is true), and
[I-D.ietf-tsvwg-rfc5405bis] provide current guidance on using this the PMTU value can be set if
PMTUD is disabled (the boolean is false)

o CONFIG_DELAYED_SACK.SCTP:
Pass 1 primitive / event: 'Configure delayed SACK timer'
Parameters: one boolean value (delayed SACK on/off), timer value with UDP.
(optional), number of packets to wait for (default 2)
Comments: If delayed SACK is enabled, SCTP will send a SACK upon
either receiving the provided number of packets or when the timer
expires, whatever occurs first.

o ADD_SUBFLOW.MPTCP: CONFIG_RTO.SCTP:
Pass 1 primitive / event: not specified 'Configure RTO calculation'
Parameters: local IP address and optionally the local port number init (optional), min (optional), max (optional)
Comments: This adjusts the application specifies the local IP address initial, minimum and port
number that must be used for a new subflow. maximum RTO
values.

o ADD_ADDR.SCTP: SET_COOKIE_LIFE.SCTP:
Pass 1 primitive / event: Change Local Address / Set Peer Primary 'Set Cookie life value'
Parameters: local IP address cookie life value

o REM_SUBFLOW.MPTCP: SET_MAX_BURST.SCTP:
Pass 1 primitive / event: not specified 'Set maximum burst'
Parameters: local IP address, local port number, remote IP
address, remote port number max burst value
Comments: not all implementations allow values above the application removes the subflow specified by the IP/
port-pair. The MPTCP implementation must trigger a removal default
of the
subflow that belongs to this IP/port-pair. 4.

o REM_ADDR.SCTP: SET_PARTIAL_DELIVERY_POINT.SCTP:
Pass 1 primitive / event: Change Local Address / Set Peer Primary 'Set Partial Delivery Point'
Parameters: local IP address partial delivery point (integer)
Comments: this parameter must be smaller or equal to the socket
receive buffer size.

o CHECKSUM.UDP:
Pass 1 primitive / event: 'DISABLE_CHECKSUM'.
Parameters: 0 when no checksum is used at sender, 1 for checksum
at sender (default). (default)

o CHECKSUM_REQUIRED.UDP:
Pass 1 primitive / event: 'REQUIRE_CHECKSUM'.
Parameter: 0 when checksum is required at receiver, 1 to allow
zero checksum at receiver (default). (default)

o SET_CHECKSUM_COVERAGE.UDP-Lite:
Pass 1 primitive / event: 'SET_CHECKSUM_COVERAGE'. 'SET_CHECKSUM_COVERAGE'
Parameters: Coverage length at sender (default maximum coverage)

o SET_MIN_CHECKSUM_COVERAGE.UDP-Lite:
Pass 1 primitive / event: 'SET_MIN_COVERAGE'.
Parameter: Coverage length at receiver (default minimum coverage)

o SET_DF.UDP(-Lite):
Pass 1 primitive event: 'SET_DF'.
Parameter: 0 when DF is not set (default), 1 when DF is set. set

o SET_TTL.UDP(-Lite) (IPV6_UNICAST_HOPS):
Pass 1 primitive / event: 'SET_TTL' and 'SET_IPV6_UNICAST_HOPS'
Parameters: IPv4 TTL value or IPv6 Hop Count value
Comments: This allows an application to change the IPv4 TTL of
IPv6 Hop count value for outgoing UDP(-Lite) datagrams.

o GET_TTL.UDP(-Lite) (IPV6_UNICAST_HOPS):
Pass 1 primitive / event: 'GET_TTL' and 'GET_IPV6_UNICAST_HOPS'
Returns: IPv4 TTL value or IPv6 Hop Count value
Comments: This allows an application to read the the IPv4 TTL of
IPv6 Hop count value from a received UDP(-Lite) datagram.

o SET_ECN.UDP(-Lite):
Pass 1 primitive / event: 'SET_ECN'
Parameters: ECN value
Comments: This allows a UDP(-Lite) application to set the ECN
codepoint field for outgoing UDP(-Lite) datagrams.

o GET_ECN.UDP(-Lite):
Pass 1 primitive / event: 'GET_ECN'
Parameters: ECN value
Comments: This allows a UDP(-Lite) application to read the ECN
codepoint field from a received UDP(-Lite) datagram.

o SET_IP_OPTIONS.UDP(-Lite):
Pass 1 primitive / event: 'SET_IP_OPTIONS'
Parameters: options
Comments: This allows a UDP(-Lite) application to set IP Options
for outgoing UDP(-Lite) datagrams. These options can at least be
the Source Route, Record Route, and Time Stamp option.

o GET_IP_OPTIONS.UDP(-Lite):
Pass 1 primitive / event: 'GET_IP_OPTIONS'
Returns: options
Comments: This allows a UDP(-Lite) application to receive any IP
options that are contained in a received UDP(-Lite) datagram.

o AUTHENTICATION_NOTIFICATION-EVENT.SCTP: CONFIGURE.LEDBAT:
Pass 1 primitive / event: 'AUTHENTICATION notification'
Returns: information regarding key management. N/A
Parameters: enable (boolean), TARGET, ALLOWED_INCREASE, GAIN_INC,
GAIN_DEC, BASE_HISTORY, CURRENT_FILTER, INIT_CWND, MIN_CWND
Comments: enable is a newly invented parameter that enables or
disables the whole LEDBAT service.

TERMINATION:
Gracefully or forcefully closing a connection, or being informed
about this event happening.

o CLOSE.TCP:
Pass 1 primitive / event: 'close'
Comments: this terminates the sending side of a connection after
reliably delivering all remaining data.

o CLOSE.SCTP:
Pass 1 primitive / event: 'Shutdown'
Comments: this terminates a connection after reliably delivering
all remaining data.

o CLOSE.UDP(-Lite):
Pass 1 primitive event: 'CLOSE'
Comments: No further UDP(-Lite) datagrams are sent/received on
this connection.

o ABORT.TCP:
Pass 1 primitive / event: 'abort'
Comments: this terminates a connection without delivering
remaining data and sends an error message to the other side.

o ABORT.SCTP:
Pass 1 primitive / event: 'abort'
Parameters: abort reason to be given to the peer (optional)
Comments: this terminates a connection without delivering
remaining data and sends an error message to the other side.

o TIMEOUT.TCP:
Pass 1 primitive / event: 'USER TIMEOUT' event
Comments: the application is informed that the connection is
aborted. This event is executed on expiration of the timeout set
in CONNECTION.ESTABLISHMENT.CONNECT.TCP (possibly adjusted in
CONNECTION.MAINTENANCE.CHANGE-TIMEOUT.TCP).
CONNECTION.MAINTENANCE.CHANGE_TIMEOUT.TCP).

o TIMEOUT.SCTP:
Pass 1 primitive / event: 'COMMUNICATION LOST' event
Comments: the application is informed that the connection is
aborted. this event is executed on expiration of the timeout that
should be enabled by default (see beginning of section 8.3 in
[RFC4960]) and was possibly adjusted in
CONNECTION.MAINTENANCE.CHANGE-TIMEOOUT.SCTP.
CONNECTION.MAINTENANCE.CHANGE_TIMEOOUT.SCTP.

o ABORT-EVENT.TCP:
Pass 1 primitive / event: not specified.

o ABORT-EVENT.SCTP:
Pass 1 primitive / event: 'COMMUNICATION LOST' event
Returns: abort reason from the peer (if available)
Comments: the application is informed that the other side has
aborted the connection using CONNECTION.TERMINATION.ABORT.SCTP.

o CLOSE-EVENT.TCP:
Pass 1 primitive / event: not specified.

o CLOSE-EVENT.SCTP:
Pass 1 primitive / event: 'SHUTDOWN COMPLETE' event
Comments: the application is informed that
CONNECTION.TERMINATION.CLOSE.SCTP was successfully completed.

4.2. DATA Transfer Related Primitives

All primitives in this section refer to an existing connection, i.e.
a connection that was either established or made available for
receiving data (although this is optional for the primitives of UDP(-
Lite)). In addition to the listed parameters, all sending primitives
contain a reference to a data block and all receiving primitives
contain a reference to available buffer space for the data. Note
that CONNECT.TCP and LISTEN.TCP in the ESTABLISHMENT and AVAILABILITY
category also allow to transfer data (an optional user message)
before the connection is fully established.

o SEND.TCP:
Pass 1 primitive / event: 'send'
Parameters: timeout (optional)
Comments: this gives TCP a data block for reliable transmission to
the TCP on the other side of the connection. The timeout can be
configured with this call whenever data are sent (see also
CONNECTION.MAINTENANCE.CHANGE-TIMEOUT.TCP).

o SEND.SCTP:
Pass 1 primitive / event: 'Send'
Parameters: stream number; context (optional); socket (optional);
unordered flag (optional); no-bundle flag (optional); payload
protocol-id (optional); pr-policy (optional) pr-value (optional);
sack-immediately flag (optional); key-id (optional)
Comments: this gives SCTP a data block for transmission to the
SCTP on the other side of the connection (SCTP association). The
'stream number' denotes the stream to be used. The 'context'
number can later be used to refer to the correct message when an
error is reported. The 'socket' can be used to state which path
should be preferred, if there are multiple paths available (see
also CONNECTION.MAINTENANCE.SETPRIMARY.SCTP). The data block can
be delivered out-of-order if the 'unordered flag' is set. The
'no-bundle flag' can be set to indicate a preference to avoid
bundling. The 'payload protocol-id' is a number that will, if
provided, be handed over to the receiving application. Using pr-
policy and pr-value the level of reliability can be controlled.
The sack-immediately 'sack-immediately' flag can be used to indicate that the peer
should not delay the sending of a SACK corresponding to the
provided user message. If specified, the provided key-id is used
for authenticating the user message.

o SEND.UDP(-Lite):
Pass 1 primitive / event: 'SEND'
Parameters: IP Address and Port Number of the destination endpoint
(optional if connected).
Comments: This provides a message for unreliable transmission
using UDP(-Lite) to the specified transport address. IP address
and Port may be omitted for connected UDP(-Lite) sockets. All
CONNECTION.MAINTENANCE.SET_*.UDP(-Lite) primitives apply per
message sent.

o RECEIVE.TCP:
Pass 1 primitive / event: 'receive'.

o RECEIVE.SCTP:
Pass 1 primitive / event: 'DATA ARRIVE' notification, followed by
'Receive'
Parameters: stream number (optional)
Returns: stream sequence number (optional), partial flag
(optional)
Comments: if the 'stream number' is provided, the call to receive
only receives data on one particular stream. If a partial message
arrives, this is indicated by the 'partial flag', and then the
'stream sequence number' must be provided such that an application
can restore the correct order of data blocks that comprise an
entire message. Additionally, a delivery number lets the
application detect reordering.

o RECEIVE.UDP(-Lite):
Pass 1 primitive / event: 'RECEIVE',
Parameters: Buffer for received datagram.
Comments: All CONNECTION.MAINTENANCE.GET_*.UDP(-Lite) primitives
apply per message received.

o SENDFAILURE-EVENT.SCTP:
Pass 1 primitive / event: 'SEND FAILURE' notification, optionally
followed by 'Receive Unsent Message' or 'Receive Unacknowledged
Message'
Returns: cause code; context; unsent or unacknowledged message
(optional)
Comments: 'cause code' indicates the reason of the failure, and
'context' is the context number if such a number has been provided
in DATA.SEND.SCTP, for later use with 'Receive Unsent Message' or
'Receive Unacknowledged Message', respectively. These primitives
can be used to retrieve the complete unsent or unacknowledged message (or
part of the message, in case a part was delivered) if desired.

o SEND_FAILURE.UDP(-Lite): SEND_FAILURE.UDP(-Lite):
Pass 1 primitive / event: 'SEND'
Comments: This may be used to probe for the effective PMTU when
using in combination with the 'MAINTENANCE.SET_DF' primitive.

o SENDER_DRY-EVENT.SCTP:
Pass 1 primitive / event: 'SENDER DRY' notification
Comments: This informs the application that the stack has no more
user data to send.

o PARTIAL_DELIVERY_ABORTED-EVENT.SCTP:
Pass 1 primitive / event: 'SEND'
Comment: 'PARTIAL DELIVERY ABORTED' notification
Comments: This may be used to probe for informs the effective PMTU when
using in combination with receiver of a partial message that the 'MAINTENANCE.SET_DF' primitive.
further delivery of the message has been aborted.

5. Pass 3

This section presents the superset of all transport service features Transport Features in all
protocols that were discussed in the preceding sections, based on the
list of primitives in pass 2 but also on text in pass 1 to include
features that can be configured in one protocol and are static
properties in another (congestion control, for example). Again, some
minor details are omitted for the sake of generalization -- e.g., TCP
may provide various different IP options, but only source route is
mandatory to implement, and this detail is not visible in the Pass 3
feature "Specify IP Options".

5.1. CONNECTION Related Transport Service Features

ESTABLISHMENT:
Active creation of a connection from one transport endpoint to one or
more transport endpoints.

o Connect
Protocols: TCP, SCTP, UDP(-Lite)

o Specify which IP Options must always be used
Protocols: TCP

o Request multiple streams
Protocols: SCTP

o Limit the number of inbound streams
Protocols: SCTP

o Specify number of attempts and/or timeout for the first
establishment message
Protocols: TCP, SCTP

o Obtain multiple sockets
Protocols: SCTP

o Disable MPTCP
Protocols: MPTCP

o Specify which chunk types must always be authenticated
Protocols: SCTP
Comments: DATA, ACK etc. are different 'chunks' in SCTP; one or
more chunks may be included in a single packet.

o Indicate an Adaptation Layer (via an adaptation code point)
Protocols: SCTP

o Request to negotiate interleaving of user messages
Protocols: SCTP

o Hand over a message to transfer (possibly multiple times) before
connection establishment
Protocols: TCP

o Hand over a message to transfer during connection establishment
Protocols: SCTP

o Enable UDP encapsulation with a specified remote UDP port number
Protocols: SCTP

AVAILABILITY:
Preparing to receive incoming connection requests.

o Listen, 1 specified local interface
Protocols: TCP, SCTP, UDP(-Lite)

o Listen, N specified local interfaces
Protocols: SCTP, UDP(-Lite)

o Listen, all local interfaces
Protocols: TCP, SCTP, UDP(-Lite)

o Obtain requested number of streams
Protocols: SCTP

o Limit the number of inbound streams
Protocols: SCTP

o Specify which IP Options must always be used
Protocols: TCP

o Disable MPTCP
Protocols: MPTCP

o Specify which chunk types must always be authenticated
Protocols: SCTP
Comments: DATA, ACK etc. are different 'chunks' in SCTP; one or
more chunks may be included in a single packet.

o Indicate an Adaptation Layer (via an adaptation code point)
Protocols: SCTP

MAINTENANCE:
Adjustments made to an open connection, or notifications about it.
NOTE: all features except "set primary path" in this category apply
to one out of multiple possible paths (identified via sockets) in
SCTP, whereas TCP uses only one path (one socket).

o Change timeout for aborting connection (using retransmit limit or
time value)
Protocols: TCP, SCTP

o Control advertising Suggest timeout for aborting connection to remote
endpoint the peer
Protocols: TCP

o Disable Nagle algorithm
Protocols: TCP, SCTP
Comments: This is not specified in [RFC4960] but in [RFC6458].

o Request an immediate heartbeat, returning success/failure
Protocols: SCTP

o Set protocol parameters
Protocols: SCTP
SCTP parameters: RTO.Initial; RTO.Min; RTO.Max; Max.Burst;
RTO.Alpha; RTO.Beta; Valid.Cookie.Life; Association.Max.Retrans;
Path.Max.Retrans; Max.Init.Retransmits; HB.interval; HB.Max.Burst;
PotentiallyFailed.Max.Retrans; Primary.Switchover.Max.Retrans;
Remote.UDPEncapsPort
Comments: as transport layer features from other protocols are
added, it might make sense to separate out some of these
parameters -- e.g., if a different protocol provides means to
adjust the RTO calculation there could be a common feature for
them called "adjust RTO calculation".

o Notification of Excessive Retransmissions (early warning below
abortion threshold)
Protocols: TCP TCP

o Add path
Protocols: MPTCP, SCTP
MPTCP Parameters: source-IP; source-Port; destination-IP;
destination-Port
SCTP Parameters: local IP address

o Remove path
Protocols: MPTCP, SCTP
MPTCP Parameters: source-IP; source-Port; destination-IP;
destination-Port
SCTP Parameters: local IP address

o Set primary path
Protocols: SCTP

o Suggest primary path to the peer
Protocols: SCTP

o Notification of ICMP error message arrival Configure Path Switchover
Protocols: TCP, UDP(-Lite) SCTP

o Obtain status (query or notification)
Protocols: SCTP, MPTCP
SCTP parameters: association connection state; socket destination
transport address list; socket destination transport address reachability
states; current local and peer receiver window size; sizes; current
local congestion window sizes; number of unacknowledged DATA
chunks; number of DATA chunks pending receipt; primary path; most
recent SRTT on primary path; RTO on primary path; SRTT and RTO on
other destination addresses; socket becoming active / inactive MTU per path; interleaving supported
yes/no
MPTCP parameters: subflow-list (identified by source-IP; source-
Port; destination-IP; destination-Port)

o Specify DSCP field
Protocols: TCP, SCTP, UDP(-Lite)

o Notification of ICMP error message arrival
Protocols: TCP, UDP(-Lite)

o Change authentication parameters
Protocols: SCTP

o Obtain authentication information
Protocols: SCTP

o Set primary path
Protocols: SCTP

o Reset Stream
Protocols: SCTP

o Notification of Stream Reset
Protocols: STCP

o Reset Association
Protocols: SCTP

o Notification of Association Reset
Protocols: STCP

o Add Streams
Protocols: SCTP

o Notification of Added Stream
Protocols: STCP

o Set peer primary path Choose a scheduler to operate between streams of an association
Protocols: SCTP

o Configure priority or weight for a scheduler
Protocols: SCTP

o Specify DSCP IPv6 flow label field
Protocols: TCP, SCTP, UDP(-Lite) SCTP

o Add subflow Configure send buffer size
Protocols: MPTCP
MPTCP Parameters: source-IP; source-Port; destination-IP;
destination-Port SCTP

o Remove subflow Configure receive buffer (and rwnd) size
Protocols: MPTCP
MPTCP Parameters: source-IP; source-Port; destination-IP;
destination-Port SCTP

o Add local address Configure message fragmentation
Protocols: SCTP

o Remove local address Configure PMTUD
Protocols: SCTP

o Configure delayed SACK timer
Protocols: SCTP

o Set Cookie life value
Protocols: SCTP

o Set maximum burst
Protocols: SCTP

o Configure size where messages are broken up for partial delivery
Protocols: SCTP

o Disable checksum when sending
Protocols: UDP

o Disable checksum requirement when receiving
Protocols: UDP

o Specify checksum coverage used by the sender
Protocols: UDP-Lite

o Specify minimum checksum coverage required by receiver
Protocols: UDP-Lite

o Specify DF field
Protocols: UDP(-Lite)

o Specify TTL/Hop count field
Protocols: UDP(-Lite)

o Obtain TTL/Hop count field
Protocols: UDP(-Lite)

o Specify ECN field
Protocols: UDP(-Lite)

o Obtain ECN field
Protocols: UDP(-Lite)

o Specify IP Options
Protocols: UDP(-Lite)

o Obtain IP Options
Protocols: UDP(-Lite)

o Enable and configure "Low Extra Delay Background Transfer"
Protocols: A protocol implementing the LEDBAT congestion control
mechanism

TERMINATION:
Gracefully or forcefully closing a connection, or being informed
about this event happening.

o Close after reliably delivering all remaining data, causing an
event informing the application on the other side
Protocols: TCP, SCTP
Comments: A TCP endpoint locally only closes the connection for
sending; it may still receive data afterwards.

o Abort without delivering remaining data, causing an event
informing the application on the other side
Protocols: TCP, SCTP
Comments: In SCTP a reason can optionally be given by the
application on the aborting side, which can then be received by
the application on the other side.

o Timeout event when data could not be delivered for too long
Protocols: TCP, SCTP
Comments: the timeout is configured with CONNECTION.MAINTENANCE
"Change timeout for aborting connection (using retransmit limit or
time value)".

5.2. DATA Transfer Related Transport Service Features

All features in this section refer to an existing connection, i.e. a
connection that was either established or made available for
receiving data. Note that TCP allows to transfer data (a single
optional user message, possibly arriving multiple times) before the
connection is fully established. Reliable data transfer entails
delay -- e.g. for the sender to wait until it can transmit data, or
due to retransmission in case of packet loss.

5.2.1. Sending Data

All features in this section are provided by DATA.SEND from pass 2.
DATA.SEND is given a data block from the application, which we here
call a "message" if the beginning and end of the data block can be
identified at the receiver, and "data" otherwise.

o Reliably transfer data, with congestion control
Protocols: TCP

o Reliably transfer a message, with congestion control
Protocols: SCTP

o Unreliably transfer a message, with congestion control
Protocols: SCTP

o Unreliably transfer a message, without congestion control
Protocols: UDP(-Lite)

o Configurable Message Reliability
Protocols: SCTP

o Choice of stream
Protocols: SCTP

o Choice of path (destination address)
Protocols: SCTP

o Choice between unordered (potentially faster) or ordered delivery
of messages
Protocols: SCTP

o Request not to bundle messages
Protocols: SCTP

o Specifying a "payload protocol-id" (handed over as such by the
receiver)
Protocols: SCTP

o Specifying a key id to be used to authenticate a message
Protocols: SCTP

o Request not to delay the acknowledgement (SACK) of a message
Protocols: SCTP

5.2.2. Receiving Data

All features in this section are provided by DATA.RECEIVE from pass
2. DATA.RECEIVE fills a buffer provided by the application, with
what we here call a "message" if the beginning and end of the data
block can be identified at the receiver, and "data" otherwise.

o Receive data (with no message delineation)
Protocols: TCP

o Receive a message
Protocols: SCTP, UDP(-Lite)

o Choice of stream to receive from
Protocols: SCTP

o Information about partial message arrival
Protocols: SCTP
Comments: In SCTP, partial messages are combined with a stream
sequence number so that the application can restore the correct
order of data blocks an entire message consists of.

o Obtain a message delivery number
Protocols: SCTP
Comments: This number can let applications detect and, if desired,
correct reordering.

5.2.3. Errors

This section describes sending failures that are associated with a
specific call to DATA.SEND from pass 2.

o Notification of an unsent messages (part of a) message
Protocols: SCTP, UDP(-Lite)

o Notification of an unacknowledged messages (part of a) message
Protocols: SCTP

o Notification that the stack has no more user data to send
Protocols: SCTP

o Notification to a receiver that a partial message delivery has
been aborted
Protocols: SCTP

6. Acknowledgements

The authors would like to thank (in alphabetical order) Bob Briscoe,
Gorry Fairhurst, David Hayes, Tom Jones, Karen Nielsen and Nielsen, Joe Touch and
Brian Trammell for providing valuable feedback on this document. We
especially thank to Christoph Paasch for providing input related to
Multipath TCP. This work has received funding from the European
Union's Horizon 2020 research and innovation programme under grant
agreement No. 644334 (NEAT). The views expressed are solely those of
the author(s).

7. IANA Considerations

XX RFC ED - PLEASE REMOVE THIS SECTION XXX

This memo includes no request to IANA.

8. Security Considerations

Security will be

Authentication, confidentiality protection, and integrity protection
are identified as Transport Features by [RFC8095]. As currently
deployed in the Internet, these features are generally provided by a
protocol or layer on top of the transport protocol; no current full-
featured standards-track transport protocol provides these features
on its own. Therefore, these features are not considered in future versions this
document, with the exception of this document. native authentication capabilities of
SCTP for which the security considerations in [RFC4895] apply.

9. References

9.1. Normative References

[I-D.ietf-tsvwg-rfc5405bis]
Eggert, L.,

[FJ16] Fairhurst, G., and G. Shepherd, "UDP Usage
Guidelines", draft-ietf-tsvwg-rfc5405bis-07 and T. Jones, "Features of the User Datagram
Protocol (UDP) and Lightweight UDP (UDP-Lite) Transport
Protocols", draft-ietf-taps-transports-usage-udp-00 (work
in progress), November 2015. 2016.

[I-D.ietf-tsvwg-sctp-ndata]
Stewart, R., Tuexen, M., Loreto, S., and R. Seggelmann,
"Stream Schedulers and User Message Interleaving for the
Stream Control Transmission Protocol",
draft-ietf-tsvwg-sctp-ndata-08 (work in progress),
October 2016.

[RFC0793] Postel, J., "Transmission Control Protocol", STD 7,
RFC 793, DOI 10.17487/RFC0793, September 1981,
<http://www.rfc-editor.org/info/rfc793>.

[RFC1122] Braden, R., Ed., "Requirements for Internet Hosts -
Communication Layers", STD 3, RFC 1122, DOI 10.17487/
RFC1122, October 1989,
<http://www.rfc-editor.org/info/rfc1122>.

[RFC4960] Stewart, R., Ed., "Stream Control Transmission Protocol",
RFC 4960, DOI 10.17487/RFC4960, September 2007,
<http://www.rfc-editor.org/info/rfc4960>.

[RFC5482] Eggert, L. and F. Gont, "TCP User Timeout Option",
RFC 5482, DOI 10.17487/RFC5482, March 2009,
<http://www.rfc-editor.org/info/rfc5482>.

9.2. Informative References

[FA16] Fairhurst, Ed., G., Trammell, Ed., B., and M. Kuehlewind,
Ed., "Services provided by IETF transport protocols and
congestion control mechanisms",
draft-ietf-taps-transports-12.txt (work in progress),
October 2016.

[FJ16] Fairhurst, G. and T. Jones, "Features of the User Datagram
Protocol (UDP) and Lightweight UDP (UDP-Lite) Transport
Protocols", draft-fairhurst-taps-transports-usage-udp-03
(work in progress), October 2016.

[RFC0854] Postel, J. and J. Reynolds, "Telnet Protocol
Specification", STD 8, RFC 854, DOI 10.17487/RFC0854,
May 1983, <http://www.rfc-editor.org/info/rfc854>.

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/
RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.

[RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition
of Explicit Congestion Notification (ECN) to IP",
RFC 3168, DOI 10.17487/RFC3168, September 2001,
<http://www.rfc-editor.org/info/rfc3168>.

[RFC3260] Grossman, D., "New Terminology and Clarifications for
Diffserv", RFC 3260, DOI 10.17487/RFC3260, April 2002,
<http://www.rfc-editor.org/info/rfc3260>.

[RFC3758] Stewart, R., Ramalho, M., Xie, Q., Tuexen, M., and P.
Conrad, "Stream Control Transmission Protocol (SCTP)
Partial Reliability Extension", RFC 3758, DOI 10.17487/
RFC3758, May 2004,
<http://www.rfc-editor.org/info/rfc3758>.

[RFC3828] Larzon, L-A., Degermark, M., Pink, S., Jonsson, L-E., Ed.,
and G. Fairhurst, Ed., "The Lightweight User Datagram
Protocol (UDP-Lite)", RFC 3828, DOI 10.17487/RFC3828,
July 2004, <http://www.rfc-editor.org/info/rfc3828>.

[RFC4895] Tuexen, M., Stewart, R., Lei, P., and E. Rescorla,
"Authenticated Chunks for the Stream Control Transmission
Protocol (SCTP)", RFC 4895, DOI 10.17487/RFC4895,
August 2007, <http://www.rfc-editor.org/info/rfc4895>. <http://www.rfc-editor.org/info/rfc4895>.

[RFC4960] Stewart, R., Ed., "Stream Control Transmission Protocol",
RFC 4960, DOI 10.17487/RFC4960, September 2007,
<http://www.rfc-editor.org/info/rfc4960>.

[RFC5061] Stewart, R., Xie, Q., Tuexen, M., Maruyama, S., and M.
Kozuka, "Stream Control Transmission Protocol (SCTP)
Dynamic Address Reconfiguration", RFC 5061, DOI 10.17487/
RFC5061, September 2007,
<http://www.rfc-editor.org/info/rfc5061>.

[RFC5461]

[RFC5482] Eggert, L. and F. Gont, F., "TCP's Reaction to Soft Errors", "TCP User Timeout Option",
RFC 5461, 5482, DOI 10.17487/RFC5461, February 10.17487/RFC5482, March 2009,
<http://www.rfc-editor.org/info/rfc5461>.

[RFC6093] Gont, F. and A. Yourtchenko, "On the Implementation of the
TCP Urgent Mechanism", RFC 6093, DOI 10.17487/RFC6093,
January 2011, <http://www.rfc-editor.org/info/rfc6093>.
<http://www.rfc-editor.org/info/rfc5482>.

[RFC6182] Ford, A., Raiciu, C., Handley, M., Barre, S., and J.
Iyengar, "Architectural Guidelines for Multipath TCP
Development", RFC 6182, DOI 10.17487/RFC6182, March 2011,
<http://www.rfc-editor.org/info/rfc6182>.

[RFC6458] Stewart, R., Tuexen, M., Poon, K., Lei, P., and V.
Yasevich, "Sockets API Extensions for the Stream Control
Transmission Protocol (SCTP)", RFC 6458, DOI 10.17487/
RFC6458, December 2011,
<http://www.rfc-editor.org/info/rfc6458>.

[RFC6525] Stewart, R., Tuexen, M., and P. Lei, "Stream Control
Transmission Protocol (SCTP) Stream Reconfiguration",
RFC 6525, DOI 10.17487/RFC6525, February 2012,
<http://www.rfc-editor.org/info/rfc6525>.

[RFC6817] Shalunov, S., Hazel, G., Iyengar, J., and M. Kuehlewind,
"Low Extra Delay Background Transport (LEDBAT)", RFC 6817,
DOI 10.17487/RFC6817, December 2012,
<http://www.rfc-editor.org/info/rfc6817>.

[RFC6824] Ford, A., Raiciu, C., Handley, M., and O. Bonaventure,
"TCP Extensions for Multipath Operation with Multiple
Addresses", RFC 6824, DOI 10.17487/RFC6824, January 2013,
<http://www.rfc-editor.org/info/rfc6824>.

[RFC6897] Scharf, M. and A. Ford, "Multipath TCP (MPTCP) Application
Interface Considerations", RFC 6897, DOI 10.17487/RFC6897,
March 2013, <http://www.rfc-editor.org/info/rfc6897>.

[RFC6951] Tuexen, M. and R. Stewart, "UDP Encapsulation of Stream
Control Transmission Protocol (SCTP) Packets for End-Host
to End-Host Communication", RFC 6951, DOI 10.17487/
RFC6951, May 2013,
<http://www.rfc-editor.org/info/rfc6951>.

[RFC7053] Tuexen, M., Ruengeler, I., and R. Stewart, "SACK-
IMMEDIATELY Extension for the Stream Control Transmission
Protocol", Stream Control Transmission
Protocol", RFC 7053, DOI 10.17487/RFC7053, November 2013,
<http://www.rfc-editor.org/info/rfc7053>.

[RFC7413] Cheng, Y., Chu, J., Radhakrishnan, S., and A. Jain, "TCP
Fast Open", RFC 7413, DOI 10.17487/RFC7413, December 2014,
<http://www.rfc-editor.org/info/rfc7413>.

[RFC7496] Tuexen, M., Seggelmann, R., Stewart, R., and S. Loreto,
"Additional Policies for the Partially Reliable Stream
Control Transmission Protocol Extension", RFC 7496,
DOI 10.17487/RFC7496, April 2015,
<http://www.rfc-editor.org/info/rfc7496>.

[RFC7829] Nishida, Y., Natarajan, P., Caro, A., Amer, P., and K.
Nielsen, "SCTP-PF: A Quick Failover Algorithm for the
Stream Control Transmission Protocol", RFC 7829,
DOI 10.17487/RFC7829, April 2016,
<http://www.rfc-editor.org/info/rfc7829>.

[RFC8085] Eggert, L., Fairhurst, G., and G. Shepherd, "UDP Usage
Guidelines", BCP 145, RFC 8085, DOI 10.17487/RFC8085,
March 2017, <http://www.rfc-editor.org/info/rfc8085>.

9.2. Informative References

[RFC0854] Postel, J. and J. Reynolds, "Telnet Protocol
Specification", STD 8, RFC 854, DOI 10.17487/RFC0854,
May 1983, <http://www.rfc-editor.org/info/rfc854>.

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/
RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.

[RFC3260] Grossman, D., "New Terminology and Clarifications for
Diffserv", RFC 3260, DOI 10.17487/RFC3260, April 2002,
<http://www.rfc-editor.org/info/rfc3260>.

[RFC5461] Gont, F., "TCP's Reaction to Soft Errors", RFC 5461,
DOI 10.17487/RFC5461, February 2009,
<http://www.rfc-editor.org/info/rfc5461>.

[RFC6093] Gont, F. and A. Yourtchenko, "On the Implementation of the
TCP Urgent Mechanism", RFC 7053, 6093, DOI 10.17487/RFC7053, November 2013,
<http://www.rfc-editor.org/info/rfc7053>. 10.17487/RFC6093,
January 2011, <http://www.rfc-editor.org/info/rfc6093>.

[RFC7414] Duke, M., Braden, R., Eddy, W., Blanton, E., and A.
Zimmermann, "A Roadmap for Transmission Control Protocol
(TCP) Specification Documents", RFC 7414, DOI 10.17487/
RFC7414, February 2015,
<http://www.rfc-editor.org/info/rfc7414>.

[RFC7657] Black, D., Ed. and P. Jones, "Differentiated Services
(Diffserv) and Real-Time Communication", RFC 7657,
DOI 10.17487/RFC7657, November 2015,
<http://www.rfc-editor.org/info/rfc7657>.

[RFC7829] Nishida, Y., Natarajan, P., Caro, A., Amer, P.,

[RFC8095] Fairhurst, G., Ed., Trammell, B., Ed., and K.
Nielsen, "SCTP-PF: A Quick Failover Algorithm for the
Stream M. Kuehlewind,
Ed., "Services Provided by IETF Transport Protocols and
Congestion Control Transmission Protocol", Mechanisms", RFC 7829, 8095, DOI 10.17487/RFC7829, April 2016,
<http://www.rfc-editor.org/info/rfc7829>. 10.17487/
RFC8095, March 2017,
<http://www.rfc-editor.org/info/rfc8095>.

Appendix A. Overview of RFCs used as input for pass 1

TCP: [RFC0793], [RFC1122], [RFC5482] [RFC5482], [RFC7413]
MPTCP: [RFC6182], [RFC6824], [RFC6897]
SCTP: RFCs without a socket API specification: [RFC3758], [RFC4895],
[RFC4960], [RFC5061]. RFCs that include a socket API
specification: [RFC6458], [RFC6525], [RFC6951], [RFC7053],
[RFC7496] [RFC7829].
UDP(-Lite): See [FJ16]
LEDBAT: [RFC6817].

Appendix B. How this document was developed

This section gives an overview of the method that was used to develop
this document. It was given to contribute contributors for guidance, and it can
be helpful for future updates or extensions.

This document is only concerned with transport service features Transport Features that are
explicitly exposed to applications via primitives. It also strictly
follows RFC text: if a feature is truly relevant for an application,
the RFCs better should say so so, and in some way they should describe how to use and
configure it. Thus, the approach to follow followed for contributing
to developing this
document is was to identify the right RFCs, then analyze and process
their text.

Experimental RFCs are excluded, and so are primitives

Primitives that MAY be implemented (by the by a transport protocol). protocol were
excluded. To be included, the minimum requirement level for a
primitive to be implemented by a protocol is was SHOULD. If Where
[RFC2119]-style requirements levels are not used, primitives should be were
excluded when they are described in conjunction with statements like,
e.g.: "some implementations also provide" or "an implementation may
also". Briefly describe excluded Excluded primitives or parameters were briefly described in a subsection called "excluded primitives".
dedicated subsection.

Pass 1: Identify This began by identifying text that talks about primitives.
An API specification, abstract or not, obviously describes primitives
-- but
note that we are not *only* interested in API specifications. The text
describing the 'send' primitive in the API specified in [RFC0793],
for instance, does not say that data transfer is reliable. TCP's
reliability is clear, however, from this text in Section 1 of
[RFC0793]: "The Transmission Control Protocol (TCP) is intended for
use as a highly reliable host-to-host protocol between hosts in
packet-switched computer communication networks, and in
interconnected systems of such networks."

For the new

Some text for pass 1 subsection about the protocol you're describing,
it is recommendable to begin by subsections was developed copy+pasting all the
relevant text parts from the relevant RFCs, then adjust adjusting
terminology to match the terminology in Section 1 and adjust (shorten!) adjusting
(shortening!) phrasing to match the general style of the document. Try
An effort was made to formulate everything as a primitive description to make
such that the primitive description descriptions became as complete as possible
(e.g., the "SEND.TCP" primitive in pass 2 is explicitly described as
reliably transferring data); if there is text that is relevant for the primitives
presented in this pass but still does not fit directly under any primitive, use it as an introduction for your
subsection. However, do note that document length is a concern and
all the protocols and their services / features are already described
primitive was used in [FA16]. a subsection's introduction.

Pass 2: The main goal of this pass is unification of primitives. As
input, use your own text from Pass 1, no exterior sources. If you
find that something is missing there, fix the of primitives. As
input, only text in Pass 1. from pass 1 was used (no exterior sources). The
list in pass 2 is not done arranged by protocol ("first protocol X, here
are all the primitives; then protocol Y, here are all the primitives,
..") but by primitive ("primitive A, implemented this way in protocol
X, this way in protocol Y, ..."). We want It was a goal to obtain as many
similar pass 2 primitives as possible. This can be achieved, for For instance, this was
sometimes achieved by not always maintaining a 1:1 mapping between
pass 1 and pass 2 primitives, renaming primitives etc. Please consider For every new
primitive, the primitives
that are already there and existing primitives were considered to try to
make the ones of the protocol you
are describing them as much in line with the already existing ones coherent as possible. In other words, we would rather have a primitive with new
parameters than a new primitive that allows to send in a particular
way.

Please make primitives fit within the already existing categories and
subcategories.

For each primitive, please follow the style: following style was used:

o PRIMITIVENAME.PROTOCOL:
Pass 1 primitive / event:
Parameters:
Returns:
Comments:

The entries "Parameters", "Returns" and "Comments" may be were skipped if when
a primitive has had no parameters, no described return value or no
comments seem seemed necessary, respectively. Optional parameters must be are
followed by "(optional)". If When a default value is known, provide it
too. this was
also provided.

Pass 3: the main point of this pass is to identify transport protocol
features that are the result of static properties of protocols, for
which all protocols have to be listed together; this is then the
final list of all available features. For this, we need a list of features per
category (similar categories as in pass 2) along with the protocol
supporting it. Transport Features. This should be list was
primarily based on text from pass 2 as
input, but text 2, with additional input from pass
1 can also be used. Do not use (but no external
sources. sources).

Appendix C. Revision information

XXX RFC-Ed please remove this section prior to publication.

-00 (from draft-welzl-taps-transports): this now covers TCP based on
all TCP RFCs (this means: if you know of something in any TCP RFC
that you think should be addressed, please speak up!) as well as
SCTP, exclusively based on [RFC4960]. We decided to also incorporate
[RFC6458] for SCTP, but this hasn't happened yet. Terminology made
in line with [FA16]. [RFC8095]. Addressed comments by Karen Nielsen and
Gorry Fairhurst; various other fixes. Appendices (TCP overview and how-to-
contribute)
how-to-contribute) added.

-01: this now also covers MPTCP based on [RFC6182], [RFC6824] and
[RFC6897].

-02: included UDP, UDP-Lite, and all extensions of SCTPs. This
includes fixing the [RFC6458] omission from -00.

TODO:

-03: wrote security considerations (see review in ML); the considerations. The "how to contribute" section (which, at some point, should be
was updated to reflect how the document WAS created, not how it
SHOULD BE created)
still created; it also no longer wrongly says "Experimental RFCs are excluded". This is wrong, and
accordingly, that Experimental
RFCs must also be considered - thus, TFO
(are there more Experimental ones for TCP?). Also, include are excluded. Included LEDBAT.
SCTP: DSCP Changed abstract and SCTP_NODELAY (equivalent intro to Nagle)
reflect which protocols/mechanisms are missing in pass
1 and 2. Are we missing more (DF, TTL, ..)? What covered (TCP, MPTCP, SCTP,
UDP, UDP-Lite, LEDBAT) instead of talking about e.g.
"notification "transport
protocols". Interleaving and stream scheduling added
(draft-ietf-tsvwg-sctp-ndata). TFO added. "Set protocol parameters"
in SCTP replaced with per-parameter (or parameter group) primitives.
More primitives added, mostly previously overlooked ones from
[RFC6458]. Updated terminology (s/transport service feature/
transport feature) in line with an update of ICMP error message arrival"? Also consider
draft-ietf-tsvwg-sctp-ndata. [RFC8095]. Made
sequence of transport features / primitives more logical. Combined
MPTCP's add/rem subflow with SCTP's add/remove local address.

Authors' Addresses

Michael Welzl
University of Oslo
PO Box 1080 Blindern
Oslo, N-0316
Norway

Phone: +47 22 85 24 20
Email: michawe@ifi.uio.no
Michael Tuexen
Muenster University of Applied Sciences
Stegerwaldstrasse 39
Steinfurt 48565
Germany

Email: tuexen@fh-muenster.de

Naeem Khademi
University of Oslo
PO Box 1080 Blindern
Oslo, N-0316
Norway

Email: naeemk@ifi.uio.no