draft-ietf-avt-app-rtp-keepalive-10.txt   rfc6263.txt 
Network Working Group X. Marjou Internet Engineering Task Force (IETF) X. Marjou
Internet-Draft A. Sollaud Request for Comments: 6263 A. Sollaud
Intended status: Standards Track France Telecom Orange Category: Standards Track France Telecom Orange
Expires: September 5, 2011 March 4, 2011 ISSN: 2070-1721 June 2011
Application Mechanism for keeping alive the Network Address Translator Application Mechanism for Keeping Alive the NAT Mappings
(NAT) mappings associated to RTP/RTCP flows. Associated with RTP / RTP Control Protocol (RTCP) Flows
draft-ietf-avt-app-rtp-keepalive-10
Abstract Abstract
This document lists the different mechanisms that enable applications This document lists the different mechanisms that enable applications
using Real-time Transport Protocol (RTP) and RTP control protocol using the Real-time Transport Protocol (RTP) and the RTP Control
(RTCP) to maintain their RTP Network Address Translator (NAT) Protocol (RTCP) to keep their RTP Network Address Translator (NAT)
mappings alive. It also makes a recommendation for a preferred mappings alive. It also makes a recommendation for a preferred
mechanism. This document is not applicable to Interactive mechanism. This document is not applicable to Interactive
Connectivity Establishment (ICE) agents. Connectivity Establishment (ICE) agents.
Status of this Memo Status of This Memo
This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering This is an Internet Standards Track document.
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months This document is a product of the Internet Engineering Task Force
and may be updated, replaced, or obsoleted by other documents at any (IETF). It represents the consensus of the IETF community. It has
time. It is inappropriate to use Internet-Drafts as reference received public review and has been approved for publication by the
material or to cite them other than as "work in progress." Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
This Internet-Draft will expire on September 5, 2011. Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc6263.
Copyright Notice Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the Copyright (c) 2011 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction ....................................................2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Terminology .....................................................4
3. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Requirements ....................................................4
4. List of Alternatives for Performing RTP Keepalive . . . . . . 5 4. List of Alternatives for Performing RTP Keepalive ...............4
4.1. Transport Packet of 0-byte . . . . . . . . . . . . . . . . 5 4.1. Empty (0-Byte) Transport Packet ............................4
4.2. RTP Packet with Comfort Noise Payload . . . . . . . . . . 5 4.2. RTP Packet with Comfort Noise Payload ......................5
4.3. RTCP Packets Multiplexed with RTP Packets . . . . . . . . 5 4.3. RTCP Packets Multiplexed with RTP Packets ..................5
4.4. STUN Indication Packet . . . . . . . . . . . . . . . . . . 6 4.4. STUN Indication Packet .....................................6
4.5. RTP Packet with Incorrect Version Number . . . . . . . . . 6 4.5. RTP Packet with Incorrect Version Number ...................6
4.6. RTP Packet with Unknown Payload Type . . . . . . . . . . . 6 4.6. RTP Packet with Unknown Payload Type .......................6
5. Recommended Solution for Keepalive Mechanism . . . . . . . . . 7 5. Recommended Solution for Keepalive Mechanism ....................7
6. Media Format Exceptions . . . . . . . . . . . . . . . . . . . 7 6. Media Format Exceptions .........................................7
7. Timing and Transport Considerations . . . . . . . . . . . . . 7 7. Timing and Transport Considerations .............................7
8. RTCP Flow Keepalive . . . . . . . . . . . . . . . . . . . . . 8 8. RTCP Flow Keepalive .............................................8
9. Security Considerations . . . . . . . . . . . . . . . . . . . 9 9. Security Considerations .........................................9
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 10. Acknowledgements ...............................................9
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 9 11. References ....................................................10
12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10 11.1. Normative References .....................................10
12.1. Normative references . . . . . . . . . . . . . . . . . . . 10 11.2. Informative References ...................................10
12.2. Informative references . . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11
1. Introduction 1. Introduction
Documents [RFC4787] and [RFC5382] describe Network Address Translator [RFC4787] and [RFC5382] describe Network Address Translator (NAT)
(NAT) behaviors and point out that two key aspects of NAT are behaviors and point out that two key aspects of NAT are mappings
mappings (a.k.a. bindings) and keeping them refreshed. This (a.k.a. bindings) and keeping them refreshed. This introduces a
introduces a derived requirement for applications engaged in a derived requirement for applications engaged in a multimedia session
multimedia session involving NAT traversal: they need to generate a involving NAT traversal: they need to generate a minimum of flow
minimum of flow activity in order to create NAT mappings and maintain activity in order to create NAT mappings and maintain them.
them.
When applied to applications using the real-time transport protocol When applied to applications using the Real-time Transport Protocol
(RTP) [RFC3550], the RTP media stream packets themselves normally (RTP) [RFC3550], the RTP media stream packets themselves normally
fulfill this requirement. However there exist some cases where RTP fulfill this requirement. However, there exist some cases where RTP
does not generate the minimum required flow activity. does not generate the minimum required flow activity.
The examples are: The examples are:
o In some RTP usages, such as the Session Inititation Protocol (SIP) o In some RTP usages, such as the Session Initiation Protocol (SIP)
[RFC3550], agents can negotiate a unidirectional media stream by [RFC3261], agents can negotiate a unidirectional media stream by
using the Session Description Protocol (SDP) [RFC4566] "recvonly" using the Session Description Protocol (SDP) [RFC4566] "recvonly"
attribute on one agent and "sendonly" on the peer, as defined in attribute on one agent and "sendonly" on the peer, as defined in
[RFC3264]. [RFC3264] directs implementations not to transmit [RFC3264]. [RFC3264] directs implementations not to transmit
media on the receiving agent. In case the agent receiving the media on the receiving agent. If the agent receiving the media is
media is located in the private side of a NAT, it will never located on the private side of a NAT, it will never receive RTP
receive RTP packets from the public peer if the NAT mapping has packets from the public peer if the NAT mapping has not been
not been created. created.
o Similarly, a bidirectional media stream can be "put on hold". o Similarly, a bidirectional media stream can be "put on hold".
This is accomplished by using the SDP "sendonly" or "inactive" This is accomplished by using the SDP "sendonly" or "inactive"
attributes. Again [RFC3264] directs implementations to cease attributes. Again, [RFC3264] directs implementations to cease
transmission of media in these cases. However, doing so may cause transmission of media in these cases. However, doing so may cause
NAT bindings to timeout, and media won't be able to come off hold. NAT bindings to time out, and media won't be able to come off
hold.
o Some RTP payload formats, such as the payload format for text o Some RTP payload formats, such as the payload format for text
conversation [RFC4103], may send packets so infrequently that the conversation [RFC4103], may send packets so infrequently that the
interval exceeds the NAT binding timeouts. interval exceeds the NAT binding timeouts.
To solve these problems, an agent therefore needs to periodically To solve these problems, an agent therefore needs to periodically
send keepalive data within the outgoing RTP session of an RTP media send keepalive data within the outgoing RTP session of an RTP media
stream regardless of whether the media stream is currently inactive, stream regardless of whether the media stream is currently inactive,
sendonly, recvonly or sendrecv, and regardless of the presence or sendonly, recvonly, or sendrecv, and regardless of the presence or
value of the bandwidth attribute. value of the bandwidth attribute.
It is important to note that NAT traversals constraints also usually It is important to note that NAT traversal constraints also usually
require the agents to use Symmetric RTP / RTP Control Protocol (RTCP) require that the agents use Symmetric RTP / RTP Control Protocol
[RFC4961] in addition to RTP keepalive. (RTCP) [RFC4961] in addition to RTP keepalive.
This document first states the requirements that must be supported to This document first states the requirements that must be supported to
perform RTP keepalives (Section 3). In a second step, the document perform RTP keepalives (Section 3). In a second step, the document
reports the different mechanisms to overcome this problem reports the different mechanisms to overcome this problem
(Section 4). Section 5 finally states the recommended solution for (Section 4). Section 5 finally states the recommended solution for
RTP keepalive. Section 6 discusses some media format exceptions. RTP keepalive. Section 6 discusses some media format exceptions.
Section 7 adds details about timing and transport considerations. Section 7 adds details about timing and transport considerations.
Section 8 documents how to maintain NAT bindings for RTCP. Section 8 documents how to maintain NAT bindings for RTCP.
This document is not applicable to Interactive Connectivity This document is not applicable to Interactive Connectivity
Establishment (ICE) [RFC5245] agents. Indeed, the ICE protocol Establishment (ICE) [RFC5245] agents. Indeed, the ICE protocol,
together with Session Traversal Utilities for NAT (STUN) [RFC5389] together with Session Traversal Utilities for NAT (STUN) [RFC5389]
and Traversal Using Relays around NAT (TURN) [RFC5766] solve the and Traversal Using Relays around NAT (TURN) [RFC5766], solves the
overall Network Address Translator (NAT) traversal mechanism of media overall Network Address Translator (NAT) traversal mechanism of media
streams. In the context of RTP media streams, some agents may not streams. In the context of RTP media streams, some agents may not
require all ICE functionalities and may only need a keepalive require all ICE functionalities and may only need a keepalive
mechanism. This document thus applies to such agents, and does not mechanism. This document thus applies to such agents, and does not
apply to agents implementing ICE. apply to agents implementing ICE.
Note that if a given media uses a codec that already integrates a Note that if a given media uses a codec that already integrates a
keepalive mechanism, no additional keepalive mechanism is required at keepalive mechanism, no additional keepalive mechanism is required at
the RTP level. the RTP level.
As mentioned in Section 3.5 of [RFC5405] "It is important to note As mentioned in Section 3.5 of [RFC5405], "It is important to note
that keepalive messages are NOT RECOMMENDED for general use -- they that keepalive messages are NOT RECOMMENDED for general use -- they
are unnecessary for many applications and can consume significant are unnecessary for many applications and can consume significant
amounts of system and network resources." amounts of system and network resources".
2. Terminology 2. Terminology
In this document, the key words "MUST", "MUST NOT", "REQUIRED", In this document, the key words "MUST", "MUST NOT", "REQUIRED",
"SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY",
and "OPTIONAL" are to be interpreted as described in RFC 2119 and "OPTIONAL" are to be interpreted as described in RFC 2119
[RFC2119]. [RFC2119].
3. Requirements 3. Requirements
This section outlines the key requirements that need to be satisfied This section outlines the key requirements that need to be satisfied
in order to provide RTP media keepalive. in order to provide RTP media keepalive.
REQ-1 Some data is sent periodically within the outgoing RTP session REQ-1 Some data is sent periodically within the outgoing RTP session
for the whole duration of the RTP media stream. for the whole duration of the RTP media stream.
REQ-2 Any type of transport (e.g. UDP, TCP) MUST be supported. REQ-2 Any type of transport (e.g., UDP, TCP) MUST be supported.
REQ-3 Any media type (e.g. audio, video, text) MUST be supported. REQ-3 Any media type (e.g., audio, video, text) MUST be supported.
REQ-4 Any media format (e.g. G.711, H.263) MUST be supported. REQ-4 Any media format (e.g., G.711, H.263) MUST be supported.
REQ-5 Session signaling protocols SHOULD NOT be impacted. REQ-5 Session signaling protocols SHOULD NOT be impacted.
REQ-6 Impacts on existing software SHOULD be minimized. REQ-6 Impacts on existing software SHOULD be minimized.
REQ-7 Remote peer SHOULD NOT be impacted. REQ-7 The remote peer SHOULD NOT be impacted.
REQ-8 The support for RTP keepalive SHOULD be described in the SDP. REQ-8 The support for RTP keepalive SHOULD be described in the SDP.
REQ-9 The solution SHOULD cover the integration with RTCP. REQ-9 The solution SHOULD cover the integration with RTCP.
4. List of Alternatives for Performing RTP Keepalive 4. List of Alternatives for Performing RTP Keepalive
This section lists, in no particular order, some alternatives that This section lists, in no particular order, some alternatives that
can be used to perform a keepalive message within RTP media streams. can be used to perform a keepalive message within RTP media streams.
4.1. Transport Packet of 0-byte 4.1. Empty (0-Byte) Transport Packet
The application sends an empty transport packet (e.g. UDP packet, The application sends an empty transport packet (e.g., UDP packet,
DCCP packet). Datagram Congestion Control Protocol (DCCP) packet).
Con:
Cons:
o This alternative is specific to each transport protocol. o This alternative is specific to each transport protocol.
4.2. RTP Packet with Comfort Noise Payload 4.2. RTP Packet with Comfort Noise Payload
The application sends an RTP packet with a comfort-noise payload The application sends an RTP packet with a comfort noise payload
[RFC3389]. [RFC3389].
Cons: Cons:
o This alternative is limited to audio formats only. o This alternative is limited to audio formats only.
o Comfort Noise needs to be supported by the remote peer.
o Comfort Noise needs to be signalled in SDP offer/answer. o Comfort noise needs to be supported by the remote peer.
o Comfort noise needs to be signaled in SDP offer/answer.
o The peer is likely to render comfort noise at the other side, so o The peer is likely to render comfort noise at the other side, so
the content of the payload (the noise level) needs to be carefully the content of the payload (the noise level) needs to be carefully
chosen. chosen.
4.3. RTCP Packets Multiplexed with RTP Packets 4.3. RTCP Packets Multiplexed with RTP Packets
The application sends RTCP packets in the RTP media path itself (i.e. The application sends RTCP packets in the RTP media path itself
same tuples for both RTP and RTCP packets) [RFC5761]. RTCP packets (i.e., the same tuples for both RTP and RTCP packets) [RFC5761].
therefore maintain the NAT mappings open as long as the requirements RTCP packets therefore keep the NAT mappings open as long as the
on parameter selection are fulfilled as discussed in Section 8. requirements for parameter selection are fulfilled as discussed in
Section 8.
Note: "on hold" procedures of [RFC3264] do not impact RTCP Note: The "on hold" procedures of [RFC3264] do not impact RTCP
transmissions. transmissions.
Cons: Cons:
o Multiplexing RTP and RTCP must be supported by the remote peer. o Multiplexing RTP and RTCP must be supported by the remote peer.
o Some RTCP monitoring tools expect that RTCP packets are not o Some RTCP monitoring tools expect that RTCP packets are not
multiplexed. multiplexed.
o RTCP must be configured so that Tmin value [RFC3550] is lower or
equal to the Tr interval. o RTCP must be configured so that the Tmin value [RFC3550] is less
than or equal to the Tr interval.
4.4. STUN Indication Packet 4.4. STUN Indication Packet
The application sends a STUN [RFC5389] Binding Indication packet as The application sends a STUN [RFC5389] Binding Indication packet as
specified in ICE [RFC5245]. specified in ICE [RFC5245].
Thanks to the RTP validity check, STUN packets will be ignored by the Thanks to the RTP validity check, STUN packets will be ignored by the
RTP stack. RTP stack.
Cons: Con:
o The sending agent needs to support STUN. o The sending agent needs to support STUN.
4.5. RTP Packet with Incorrect Version Number 4.5. RTP Packet with Incorrect Version Number
The application sends an RTP packet with an incorrect version number, The application sends an RTP packet with a version number set to zero
which value is zero. (i.e., an incorrect version number).
Based on RTP specification [RFC3550], the peer should perform a Based on the RTP specification [RFC3550], the peer should perform a
header validity check, and therefore ignore these types of packet. header validity check and therefore ignore these types of packets.
Cons: Cons:
o Only four version numbers are possible. Using one of them for RTP o Only four version numbers are possible. Using one of them for RTP
keepalive would be wasteful. keepalive would be wasteful.
o [RFC4566] and [RFC3264] mandate not to send media with inactive
and recvonly attributes, however this is mitigated as no real o [RFC4566] and [RFC3264] mandate that media with inactive and
media is sent with this mechanism. recvonly attributes not be sent; however, this is mitigated, as no
real media is sent with this mechanism.
4.6. RTP Packet with Unknown Payload Type 4.6. RTP Packet with Unknown Payload Type
The application sends an RTP packet of 0 length with a dynamic The application sends an RTP packet of 0 length with a dynamic
payload type that has not been negotiated by the peers (e.g. not payload type that has not been negotiated by the peers (e.g., not
negotiated within the SDP offer/answer, and thus not mapped to any negotiated within the SDP offer/answer, and thus not mapped to any
media format). media format).
The sequence number is incremented by one for each packet, as it is The sequence number is incremented by one for each packet, as it is
sent within the same RTP session as the actual media. The timestamp sent within the same RTP session as the actual media. The timestamp
contains the same value a media packet would have at this time. The contains the same value that a media packet would have at this time.
marker bit is not significant for the keepalive packets and is thus The marker bit is not significant for the keepalive packets and is
set to zero. thus set to zero.
The SSRC is the same as for the media for which keepalive is sent. The synchronization source (SSRC) is the same as for the media for
which keepalive is sent.
Normally the peer will ignore this packet, as RTP [RFC3550] states Normally, the peer will ignore this packet, as RTP [RFC3550] states
that "a receiver MUST ignore packets with payload types that it does that "a receiver MUST ignore packets with payload types that it does
not understand". not understand".
Cons: Cons:
o [RFC4566] and [RFC3264] mandate not to send media with inactive
and recvonly attributes, however this is mitigated as no real o [RFC4566] and [RFC3264] mandate that media with inactive and
media is sent with this mechanism. recvonly attributes not be sent; however, this is mitigated, as no
real media is sent with this mechanism.
o [RFC3550] does not preclude examination of received packets by the o [RFC3550] does not preclude examination of received packets by the
peer in an attempt to determine if it is under attack. peer in an attempt to determine if it is under attack.
o The statement "RTP Packet with Unknown Payload Type" of RFC3550 is
not always observed in real life. o The statement "a receiver MUST ignore packets with payload types
o There is no RTCP reporting for the keepalive packets as RFC3550 that it does not understand" of [RFC3550] is not always observed
mandates to ignore "RTP Packet with Unknown Payload Type". in real life.
o There is no RTCP reporting for the keepalive packets, as [RFC3550]
mandates that RTP packets with payload types that the receiver
does not understand be ignored.
o Some RTP payload formats do not handle gaps in RTP sequence number o Some RTP payload formats do not handle gaps in RTP sequence number
well. well.
5. Recommended Solution for Keepalive Mechanism 5. Recommended Solution for Keepalive Mechanism
The RECOMMENDED mechanism is the "RTCP packets multiplexed with RTP The RECOMMENDED mechanism is that discussed in "RTCP Packets
packets" (Section 4.3). This mechanism is desirable because it Multiplexed with RTP Packets" (Section 4.3). This mechanism is
reduces the number of ports when RTP and RTCP are used. It also has desirable because it reduces the number of ports when RTP and RTCP
the advantage of taking into account RTCP aspects, which is not the are used. It also has the advantage of taking into account RTCP
case of other mechanisms. aspects, which is not the case with other mechanisms.
Other mechanisms (Section 4.1, Section 4.2, Section 4.4, Section 4.5, Other mechanisms (Sections 4.1, 4.2, 4.4, 4.5, and 4.6) are NOT
Section 4.6) are NOT RECOMMENDED. RECOMMENDED.
6. Media Format Exceptions 6. Media Format Exceptions
When a given media format does not allow the keepalive solution When a given media format does not allow the keepalive solution
recommended in Section 5, an alternative mechanism SHOULD be defined recommended in Section 5, an alternative mechanism SHOULD be defined
in the payload format specification for this media format. in the payload format specification for this media format.
7. Timing and Transport Considerations 7. Timing and Transport Considerations
An application supporting this specification MUST transmit either An application supporting this specification MUST transmit either
keepalive packets or media packets at least once every Tr seconds keepalive packets or media packets at least once every Tr seconds
during the whole duration of the media session. during the whole duration of the media session.
Tr has different value according to the transport protocol Tr has different value according to the transport protocol.
For UDP, the minimum RECOMMENDED Tr value is 15 seconds, and Tr For UDP, the minimum RECOMMENDED Tr value is 15 seconds, and Tr
SHOULD be configurable to larger values. SHOULD be configurable to larger values.
For TCP, the recommended Tr value is 7200 seconds. For TCP, the recommended Tr value is 7200 seconds.
When using the "RTCP packets multiplexed with RTP packets" solution When using the "RTCP packets multiplexed with RTP packets" solution
for keepalive, Tr MUST comply with the RTCP timing rules of (Section 4.3) for keepalive, Tr MUST comply with the RTCP timing
[RFC3550]. rules of [RFC3550].
Keepalive packets within a particular RTP session MUST use the tuple Keepalive packets within a particular RTP session MUST use the tuple
(source IP address, source TCP/UDP ports, target IP address, target (source IP address, source TCP/UDP port, target IP address, target
TCP/UDP Port) of the regular RTP packets. TCP/UDP port) of the regular RTP packets.
The agent SHOULD only send RTP keepalive when it does not send The agent SHOULD only send RTP keepalive when it does not send
regular RTP packets. regular RTP packets.
8. RTCP Flow Keepalive 8. RTCP Flow Keepalive
RTCP packets are sent periodically and can thus normally maintain the RTCP packets are sent periodically and can thus normally keep the NAT
NAT mappings open as long as they are sent frequently enough. There mappings open as long as they are sent frequently enough. There are
are two conditions for that. First RTCP needs to be used bi- two conditions for that. First, RTCP needs to be used
directionally and in a symmetric fashion, as described in [RFC4961]. bidirectionally and in a symmetric fashion, as described in
Secondly, RTCP needs to be sent frequently enough. However, there [RFC4961]. Secondly, RTCP needs to be sent frequently enough.
are certain configurations that can break this latter assumption. However, there are certain configurations that can break this latter
assumption.
There are two factors that need to be considered to ensure that RTCP There are two factors that need to be considered to ensure that RTCP
is sent frequently enough. First the RTCP bandwidth needs to be is sent frequently enough. First, the RTCP bandwidth needs to be
sufficiently large so that transmission will occur more frequently sufficiently large so that transmission will occur more frequently
than the longest acceptable packet transmission interval (Tr). The than the longest acceptable packet transmission interval (Tr). The
worst case RTCP interval (Twc) can be calculated using this formula worst-case RTCP interval (Twc) can be calculated using this formula
by inserting the max value of the following parameters: by inserting the max value of the following parameters:
o Maximum RTCP packet size (avg_rtcp_size_max) o Maximum RTCP packet size (avg_rtcp_size_max)
o Maximum number of participants (members_max) o Maximum number of participants (members_max)
o RTCP receiver bandwidth (rtcp_bw) o RTCP receiver bandwidth (rtcp_bw)
The RTCP bandwidth value to use here is for a worst case, which will The RTCP bandwidth value to use here is for a worst case, which will
be the receiver proportion when all members are not senders except be the receiver proportion when all members except one are not
one. This can be approximated to be all members. Thus for sessions senders. This can be approximated to be all members. Thus, for
where RR and RS values are used, then rtcp_bw shall be set to RR. sessions where RR and RS values [RFC3556] are used, then rtcp_bw
For sessions where the [RFC3550] defines proportions of 1/4 for shall be set to RR. For sessions where the [RFC3550]-defined
sender and 3/4 for receivers are used, then rtcp_bw will be 5% of 3/4 proportions of RTCP bandwidth are used (i.e., 1/4 of the bandwidth
of the AS value in bits per second. for senders and 3/4 of the bandwidth for receivers), then rtcp_bw
will be 5% of 3/4 of the AS value [RFC4566] in bits per second.
Twc = 1.5 / 1.21828 * members_max * rtcp_bw / avg_rtcp_size_max * 8 Twc = 1.5 / 1.21828 * members_max * rtcp_bw / avg_rtcp_size_max * 8
The second factor is the minimum RTCP interval Tmin defined in The second factor is the minimum RTCP interval Tmin defined in
[RFC3550]. Its base value is 5 seconds, but it might also be scaled [RFC3550]. Its base value is 5 seconds, but it might also be scaled
to 360 divided by the session bandwidth in kbps. The Extended RTP to 360 divided by the session bandwidth in kbps. The Extended RTP
Profile for Real-time Transport Control Protocol (RTCP)-Based Profile for Real-time Transport Control Protocol (RTCP)-Based
Feedback (RTP/AVPF) [RFC4585] also allows for the setting of a trr- Feedback (RTP/AVPF) [RFC4585] also allows for the setting of a
int parameter which is a minimal RTCP interval for regular RTCP trr-int parameter, which is a minimal RTCP interval for regular RTCP
packets. It is also used as the Tmin value in the regular Td packets. It is also used as the Tmin value in the regular Td
calculation. An analysis of the algorithm gives that the longest calculation. An analysis of the algorithm shows that the longest
possible regular RTCP interval possible are: possible regular RTCP interval is:
RTCP_int_max = trr-int * 1.5 + Td * 1.5 / 1.21828 RTCP_int_max = trr-int * 1.5 + Td * 1.5 / 1.21828
And as long as the there is sufficient bandwidth according to And as long as there is sufficient bandwidth according to criteria 1
criteria 1, then this can be simplified by setting Td = trr-int below, then the algorithm can be simplified by setting Td = trr-int,
giving giving
RTCP_int_max = trr-int * (1.5 + 1.5 / 1.21828) = 2.73123 * trr-int RTCP_int_max = trr-int * (1.5 + 1.5 / 1.21828) = 2.73123 * trr-int
Thus the requirements on the RTCP parameters are the following for Thus, the requirements for the RTCP parameters are as follows for
functioning keepalive: functioning keepalive:
1. Ensure that sufficient RTCP bandwidth is provided by calculating 1. Ensure that sufficient RTCP bandwidth is provided by calculating
Twc and ensure that this is less than or equal to Tr. Twc, and ensure that the resulting value is less than or equal
2. If AVP or SAVP is used the Tmin value can't be greater that Tr to Tr.
divided by 1.5 / (e-3/2).
3. If AVPF or SAVPF is to be used trr-min must not be set to a 2. If AVP or SAVP [RFC3711] is used, the Tmin value can't be greater
greater value than Tr / 3. than Tr divided by 1.5 / (e-3/2).
3. If AVPF or SAVPF [RFC5124] is to be used, trr-min must not be set
to a value greater than Tr / 3.
9. Security Considerations 9. Security Considerations
The RTP keepalive packets are sent on the same path as regular RTP The RTP keepalive packets are sent on the same path as regular RTP
media packets and may be perceived as an attack by a peer. However, media packets and may be perceived as an attack by a peer. However,
[RFC3550] mandates a peer to "ignore packets with payload types that [RFC3550] mandates that a peer "ignore packets with payload types
it does not understand". A peer that does not understand the that it does not understand". A peer that does not understand the
keepalive message will thus appropriately drop the received packets. keepalive message will thus appropriately drop the received packets.
10. IANA Considerations 10. Acknowledgements
None.
11. Acknowledgements
Jonathan Rosenberg provided the major inputs for this draft via the Jonathan Rosenberg provided the major inputs for this document via
ICE specification. Magnus Westerlund provided the text for the RTCP the ICE specification. Magnus Westerlund provided the text for the
flow keepalive section. In addition, thanks to Alfred E. Heggestad, RTCP flow keepalive section. In addition, thanks to Alfred E.
Colin Perkins, Dan Wing, Gunnar Hellstrom, Hadriel Kaplan, Randell Heggestad, Colin Perkins, Dan Wing, Gunnar Hellstrom, Hadriel Kaplan,
Jesup, Remi Denis-Courmont, Robert Sparks, and Steve Casner for their Randell Jesup, Remi Denis-Courmont, Robert Sparks, and Steve Casner
useful inputs and comments. for their useful inputs and comments.
12. References 11. References
12.1. Normative references 11.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V.
Jacobson, "RTP: A Transport Protocol for Real-Time Jacobson, "RTP: A Transport Protocol for Real-Time
Applications", STD 64, RFC 3550, July 2003. Applications", STD 64, RFC 3550, July 2003.
[RFC4961] Wing, D., "Symmetric RTP / RTP Control Protocol (RTCP)", [RFC4961] Wing, D., "Symmetric RTP / RTP Control Protocol (RTCP)",
BCP 131, RFC 4961, July 2007. BCP 131, RFC 4961, July 2007.
[RFC5405] Eggert, L. and G. Fairhurst, "Unicast UDP Usage Guidelines [RFC5405] Eggert, L. and G. Fairhurst, "Unicast UDP Usage Guidelines
for Application Designers", BCP 145, RFC 5405, for Application Designers", BCP 145, RFC 5405,
November 2008. November 2008.
[RFC5761] Perkins, C. and M. Westerlund, "Multiplexing RTP Data and [RFC5761] Perkins, C. and M. Westerlund, "Multiplexing RTP Data and
Control Packets on a Single Port", RFC 5761, April 2010. Control Packets on a Single Port", RFC 5761, April 2010.
12.2. Informative references 11.2. Informative References
[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
A., Peterson, J., Sparks, R., Handley, M., and E. A., Peterson, J., Sparks, R., Handley, M., and E.
Schooler, "SIP: Session Initiation Protocol", RFC 3261, Schooler, "SIP: Session Initiation Protocol", RFC 3261,
June 2002. June 2002.
[RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model [RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model
with Session Description Protocol (SDP)", RFC 3264, with Session Description Protocol (SDP)", RFC 3264,
June 2002. June 2002.
[RFC3389] Zopf, R., "Real-time Transport Protocol (RTP) Payload for [RFC3389] Zopf, R., "Real-time Transport Protocol (RTP) Payload for
Comfort Noise (CN)", RFC 3389, September 2002. Comfort Noise (CN)", RFC 3389, September 2002.
[RFC3556] Casner, S., "Session Description Protocol (SDP) Bandwidth
Modifiers for RTP Control Protocol (RTCP) Bandwidth",
RFC 3556, July 2003.
[RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K.
Norrman, "The Secure Real-time Transport Protocol (SRTP)",
RFC 3711, March 2004.
[RFC4103] Hellstrom, G. and P. Jones, "RTP Payload for Text [RFC4103] Hellstrom, G. and P. Jones, "RTP Payload for Text
Conversation", RFC 4103, June 2005. Conversation", RFC 4103, June 2005.
[RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session [RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
Description Protocol", RFC 4566, July 2006. Description Protocol", RFC 4566, July 2006.
[RFC4585] Ott, J., Wenger, S., Sato, N., Burmeister, C., and J. Rey, [RFC4585] Ott, J., Wenger, S., Sato, N., Burmeister, C., and J. Rey,
"Extended RTP Profile for Real-time Transport Control "Extended RTP Profile for Real-time Transport Control
Protocol (RTCP)-Based Feedback (RTP/AVPF)", RFC 4585, Protocol (RTCP)-Based Feedback (RTP/AVPF)", RFC 4585,
July 2006. July 2006.
[RFC4787] Audet, F. and C. Jennings, "Network Address Translation [RFC4787] Audet, F., Ed., and C. Jennings, "Network Address
(NAT) Behavioral Requirements for Unicast UDP", BCP 127, Translation (NAT) Behavioral Requirements for Unicast
RFC 4787, January 2007. UDP", BCP 127, RFC 4787, January 2007.
[RFC5124] Ott, J. and E. Carrara, "Extended Secure RTP Profile for
Real-time Transport Control Protocol (RTCP)-Based Feedback
(RTP/SAVPF)", RFC 5124, February 2008.
[RFC5245] Rosenberg, J., "Interactive Connectivity Establishment [RFC5245] Rosenberg, J., "Interactive Connectivity Establishment
(ICE): A Protocol for Network Address Translator (NAT) (ICE): A Protocol for Network Address Translator (NAT)
Traversal for Offer/Answer Protocols", RFC 5245, Traversal for Offer/Answer Protocols", RFC 5245,
April 2010. April 2010.
[RFC5382] Guha, S., Biswas, K., Ford, B., Sivakumar, S., and P. [RFC5382] Guha, S., Ed., Biswas, K., Ford, B., Sivakumar, S., and P.
Srisuresh, "NAT Behavioral Requirements for TCP", BCP 142, Srisuresh, "NAT Behavioral Requirements for TCP", BCP 142,
RFC 5382, October 2008. RFC 5382, October 2008.
[RFC5389] Rosenberg, J., Mahy, R., Matthews, P., and D. Wing, [RFC5389] Rosenberg, J., Mahy, R., Matthews, P., and D. Wing,
"Session Traversal Utilities for NAT (STUN)", RFC 5389, "Session Traversal Utilities for NAT (STUN)", RFC 5389,
October 2008. October 2008.
[RFC5766] Mahy, R., Matthews, P., and J. Rosenberg, "Traversal Using [RFC5766] Mahy, R., Matthews, P., and J. Rosenberg, "Traversal Using
Relays around NAT (TURN): Relay Extensions to Session Relays around NAT (TURN): Relay Extensions to Session
Traversal Utilities for NAT (STUN)", RFC 5766, April 2010. Traversal Utilities for NAT (STUN)", RFC 5766, April 2010.
Authors' Addresses Authors' Addresses
Xavier Marjou Xavier Marjou
France Telecom Orange France Telecom Orange
2, avenue Pierre Marzin 2, avenue Pierre Marzin
Lannion 22307 Lannion 22307
France France
Email: xavier.marjou@orange-ftgroup.com EMail: xavier.marjou@orange-ftgroup.com
Aurelien Sollaud Aurelien Sollaud
France Telecom Orange France Telecom Orange
2, avenue Pierre Marzin 2, avenue Pierre Marzin
Lannion 22307 Lannion 22307
France France
Email: aurelien.sollaud@orange-ftgroup.com EMail: aurelien.sollaud@orange-ftgroup.com
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