draft-ietf-tcpm-rfc3782-bis-05.txt   rfc6582.txt 
TCP Maintenance and Minor T. Henderson Internet Engineering Task Force (IETF) T. Henderson
Extensions Working Group Boeing Request for Comments: 6582 Boeing
Internet-Draft S. Floyd Obsoletes: 3782 S. Floyd
Obsoletes: 3782 (if approved) ICSI Category: Standards Track ICSI
Intended status: Standards Track A. Gurtov ISSN: 2070-1721 A. Gurtov
Expires: July 18, 2012 University of Oulu University of Oulu
Y. Nishida Y. Nishida
WIDE Project WIDE Project
January 18, 2012 April 2012
The NewReno Modification to TCP's Fast Recovery Algorithm The NewReno Modification to TCP's Fast Recovery Algorithm
draft-ietf-tcpm-rfc3782-bis-05.txt
Abstract Abstract
RFC 5681 documents the following four intertwined TCP RFC 5681 documents the following four intertwined TCP congestion
congestion control algorithms: slow start, congestion avoidance, fast control algorithms: slow start, congestion avoidance, fast
retransmit, and fast recovery. RFC 5681 explicitly allows retransmit, and fast recovery. RFC 5681 explicitly allows certain
certain modifications of these algorithms, including modifications modifications of these algorithms, including modifications that use
that use the TCP Selective Acknowledgement (SACK) option (RFC 2883), the TCP Selective Acknowledgment (SACK) option (RFC 2883), and
and modifications that respond to "partial acknowledgments" (ACKs modifications that respond to "partial acknowledgments" (ACKs that
which cover new data, but not all the data outstanding when loss was cover new data, but not all the data outstanding when loss was
detected) in the absence of SACK. This document describes a specific detected) in the absence of SACK. This document describes a specific
algorithm for responding to partial acknowledgments, referred to as algorithm for responding to partial acknowledgments, referred to as
NewReno. This response to partial acknowledgments was first proposed "NewReno". This response to partial acknowledgments was first
by Janey Hoe. This document obsoletes RFC 3782. proposed by Janey Hoe. This document obsoletes RFC 3782.
Status of this Memo
This Internet-Draft is submitted in full conformance with the Status of This Memo
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 July 18, 2012. 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/rfc6582.
Copyright Notice Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as Copyright (c) 2012 IETF Trust and the persons identified as the
the document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License. described in the Simplified BSD License.
skipping to change at page 3, line 7 skipping to change at page 2, line 34
modifications of such material outside the IETF Standards Process. modifications of such material outside the IETF Standards Process.
Without obtaining an adequate license from the person(s) controlling Without obtaining an adequate license from the person(s) controlling
the copyright in such materials, this document may not be modified the copyright in such materials, this document may not be modified
outside the IETF Standards Process, and derivative works of it may outside the IETF Standards Process, and derivative works of it may
not be created outside the IETF Standards Process, except to format not be created outside the IETF Standards Process, except to format
it for publication as an RFC or to translate it into languages other it for publication as an RFC or to translate it into languages other
than English. than English.
1. Introduction 1. Introduction
For the typical implementation of the TCP Fast Recovery algorithm For the typical implementation of the TCP fast recovery algorithm
described in [RFC5681] (first implemented in the 1990 BSD Reno described in [RFC5681] (first implemented in the 1990 BSD Reno
release, and referred to as the Reno algorithm in [FF96]), the TCP release, and referred to as the "Reno algorithm" in [FF96]), the TCP
data sender only retransmits a packet after a retransmit timeout has data sender only retransmits a packet after a retransmit timeout has
occurred, or after three duplicate acknowledgments have arrived occurred, or after three duplicate acknowledgments have arrived
triggering the Fast Retransmit algorithm. A single retransmit triggering the fast retransmit algorithm. A single retransmit
timeout might result in the retransmission of several data packets, timeout might result in the retransmission of several data packets,
but each invocation of the Fast Retransmit algorithm in RFC 5681 but each invocation of the fast retransmit algorithm in RFC 5681
leads to the retransmission of only a single data packet. leads to the retransmission of only a single data packet.
Two problems arise with Reno TCP when multiple packet losses occur Two problems arise with Reno TCP when multiple packet losses occur in
in a single window. First, Reno will often take a timeout, as a single window. First, Reno will often take a timeout, as has been
has been documented in [Hoe95]. Second, even if a retransmission documented in [Hoe95]. Second, even if a retransmission timeout is
timeout is avoided, multiple fast retransmits and window reductions avoided, multiple fast retransmits and window reductions can occur,
can occur, as documented in [F94]. When multiple packet losses as documented in [F94]. When multiple packet losses occur, if the
occur, if the SACK option [RFC2883] is available, the TCP sender SACK option [RFC2883] is available, the TCP sender has the
has the information to make intelligent decisions about which packets information to make intelligent decisions about which packets to
to retransmit and which packets not to retransmit during Fast retransmit and which packets not to retransmit during fast recovery.
Recovery. This document applies to TCP connections that are
unable to use the TCP Selective Acknowledgement (SACK) option, This document applies to TCP connections that are unable to use the
either because the option is not locally supported or TCP Selective Acknowledgment (SACK) option, either because the option
because the TCP peer did not indicate a willingness to use SACK. is not locally supported or because the TCP peer did not indicate a
willingness to use SACK.
In the absence of SACK, there is little information available to the In the absence of SACK, there is little information available to the
TCP sender in making retransmission decisions during Fast TCP sender in making retransmission decisions during fast recovery.
Recovery. From the three duplicate acknowledgments, the sender From the three duplicate acknowledgments, the sender infers a packet
infers a packet loss, and retransmits the indicated packet. After loss, and retransmits the indicated packet. After this, the data
this, the data sender could receive additional duplicate sender could receive additional duplicate acknowledgments, as the
acknowledgments, as the data receiver acknowledges additional data data receiver acknowledges additional data packets that were already
packets that were already in flight when the sender entered Fast in flight when the sender entered fast retransmit.
Retransmit.
In the case of multiple packets dropped from a single window of data, In the case of multiple packets dropped from a single window of data,
the first new information available to the sender comes when the the first new information available to the sender comes when the
sender receives an acknowledgment for the retransmitted packet (that sender receives an acknowledgment for the retransmitted packet (that
is, the packet retransmitted when Fast Retransmit was first is, the packet retransmitted when fast retransmit was first entered).
entered). If there is a single packet drop and no reordering, then If there is a single packet drop and no reordering, then the
the acknowledgment for this packet will acknowledge all of the acknowledgment for this packet will acknowledge all of the packets
packets transmitted before Fast Retransmit was entered. However, if transmitted before fast retransmit was entered. However, if there
there are multiple packet drops, then the acknowledgment for the are multiple packet drops, then the acknowledgment for the
retransmitted packet will acknowledge some but not all of the packets retransmitted packet will acknowledge some but not all of the packets
transmitted before the Fast Retransmit. We call this acknowledgment transmitted before the fast retransmit. We call this acknowledgment
a partial acknowledgment. a partial acknowledgment.
Along with several other suggestions, [Hoe95] suggested that during Along with several other suggestions, [Hoe95] suggested that during
Fast Recovery the TCP data sender responds to a partial fast recovery the TCP data sender respond to a partial acknowledgment
acknowledgment by inferring that the next in-sequence packet has been by inferring that the next in-sequence packet has been lost and
lost, and retransmitting that packet. This document describes a retransmitting that packet. This document describes a modification
modification to the Fast Recovery algorithm in RFC 5681 that to the fast recovery algorithm in RFC 5681 that incorporates a
incorporates a response to partial acknowledgments received during response to partial acknowledgments received during fast recovery.
Fast Recovery. We call this modified Fast Recovery algorithm We call this modified fast recovery algorithm NewReno, because it is
NewReno, because it is a slight but significant variation of the a slight but significant variation of the behavior that has been
basic Reno algorithm in RFC 5681. This document does not discuss the historically referred to as Reno. This document does not discuss the
other suggestions in [Hoe95] and [Hoe96], such as a change to the other suggestions in [Hoe95] and [Hoe96], such as a change to the
ssthresh parameter during Slow-Start, or the proposal to send a new ssthresh parameter during slow start, or the proposal to send a new
packet for every two duplicate acknowledgments during Fast packet for every two duplicate acknowledgments during fast recovery.
Recovery. The version of NewReno in this document also draws on The version of NewReno in this document also draws on other
other discussions of NewReno in the literature [LM97, Hen98]. discussions of NewReno in the literature [LM97] [Hen98].
We do not claim that the NewReno version of Fast Recovery described We do not claim that the NewReno version of fast recovery described
here is an optimal modification of Fast Recovery for responding to here is an optimal modification of fast recovery for responding to
partial acknowledgments, for TCP connections that are unable to use partial acknowledgments, for TCP connections that are unable to use
SACK. Based on our experiences with the NewReno modification in the SACK. Based on our experiences with the NewReno modification in the
NS simulator [NS] and with numerous implementations of NewReno, we network simulator known as ns-2 [NS] and with numerous
believe that this modification improves the performance of the Fast implementations of NewReno, we believe that this modification
Retransmit and Fast Recovery algorithms in a wide variety of improves the performance of the fast retransmit and fast recovery
scenarios. Previous versions of this RFC [RFC2582, RFC3782] provide algorithms in a wide variety of scenarios. Previous versions of this
simulation-based evidence of the possible performance gains. RFC [RFC2582] [RFC3782] provide simulation-based evidence of the
possible performance gains.
2. Terminology and Definitions 2. Terminology and Definitions
This document assumes that the reader is familiar with the terms This document assumes that the reader is familiar with the terms
SENDER MAXIMUM SEGMENT SIZE (SMSS), CONGESTION WINDOW (cwnd), and SENDER MAXIMUM SEGMENT SIZE (SMSS), CONGESTION WINDOW (cwnd), and
FLIGHT SIZE (FlightSize) defined in [RFC5681]. FLIGHT SIZE (FlightSize) defined in [RFC5681].
This document defines an additional sender-side state variable This document defines an additional sender-side state variable called
called RECOVER: "recover":
RECOVER: recover:
When in Fast Recovery, this variable records the send sequence When in fast recovery, this variable records the send sequence
number that must be acknowledged before the Fast Recovery number that must be acknowledged before the fast recovery
procedure is declared to be over. procedure is declared to be over.
3. The Fast Retransmit and Fast Recovery Algorithms in NewReno 3. The Fast Retransmit and Fast Recovery Algorithms in NewReno
3.1. Protocol Overview 3.1. Protocol Overview
The basic idea of these extensions to the Fast Retransmit and The basic idea of these extensions to the fast retransmit and fast
Fast Recovery algorithms described in Section 3.2 of [RFC5681] recovery algorithms described in Section 3.2 of [RFC5681] is as
is as follows. The TCP sender can infer, from the arrival of follows. The TCP sender can infer, from the arrival of duplicate
duplicate acknowledgments, whether multiple losses in the same acknowledgments, whether multiple losses in the same window of data
window of data have most likely occurred, and avoid taking a have most likely occurred, and avoid taking a retransmit timeout or
retransmit timeout or making multiple congestion window reductions making multiple congestion window reductions due to such an event.
due to such an event.
The NewReno modification applies to the Fast Recovery procedure that The NewReno modification applies to the fast recovery procedure that
begins when three duplicate ACKs are received and ends when either a begins when three duplicate ACKs are received and ends when either a
retransmission timeout occurs or an ACK arrives that acknowledges all retransmission timeout occurs or an ACK arrives that acknowledges all
of the data up to and including the data that was outstanding when of the data up to and including the data that was outstanding when
the Fast Recovery procedure began. the fast recovery procedure began.
3.2. Specification 3.2. Specification
The procedures specified in Section 3.2 of [RFC5681] are followed The procedures specified in Section 3.2 of [RFC5681] are followed,
with the following modifications. Note that this specification with the modifications listed below. Note that this specification
avoids the use of the key words defined in RFC 2119 [RFC2119] since avoids the use of the key words defined in RFC 2119 [RFC2119], since
it mainly provides sender-side implementation guidance for it mainly provides sender-side implementation guidance for
performance improvement, and does not affect interoperability. performance improvement, and does not affect interoperability.
1) Initialization of TCP protocol control block: 1) Initialization of TCP protocol control block:
When the TCP protocol control block is initialized, Recover is When the TCP protocol control block is initialized, recover is
set to the initial send sequence number. set to the initial send sequence number.
2) Three duplicate ACKs: 2) Three duplicate ACKs:
When the third duplicate ACK is received, the TCP sender first When the third duplicate ACK is received, the TCP sender first
checks the value of Recover to see if the Cumulative checks the value of recover to see if the Cumulative
Acknowledgment field covers more than Recover. If so, the value Acknowledgment field covers more than recover. If so, the value
of Recover is incremented to the value of the highest sequence of recover is incremented to the value of the highest sequence
number transmitted by the TCP so far. The TCP then enters Fast number transmitted by the TCP so far. The TCP then enters fast
Retransmit (step 2 of Section 3.2 of [RFC5681]). If not, the TCP retransmit (step 2 of Section 3.2 of [RFC5681]). If not, the TCP
does not enter fast retransmit and does not reset ssthresh. does not enter fast retransmit and does not reset ssthresh.
3) Response to newly acknowledged data: 3) Response to newly acknowledged data:
Step 6 of [RFC5681] specifies the response to the next ACK that Step 6 of [RFC5681] specifies the response to the next ACK that
acknowledges previously unacknowledged data. When an ACK acknowledges previously unacknowledged data. When an ACK arrives
arrives that acknowledges new data, this ACK could be the that acknowledges new data, this ACK could be the acknowledgment
acknowledgment elicited by the retransmission from step 2, or elicited by the initial retransmission from fast retransmit, or
elicited by a later retransmission. There are two cases. elicited by a later retransmission. There are two cases:
Full acknowledgments: Full acknowledgments:
If this ACK acknowledges all of the data up to and including If this ACK acknowledges all of the data up to and including
Recover, then the ACK acknowledges all the intermediate recover, then the ACK acknowledges all the intermediate segments
segments sent between the original transmission of the lost sent between the original transmission of the lost segment and
segment and the receipt of the third duplicate ACK. Set cwnd to the receipt of the third duplicate ACK. Set cwnd to either (1)
either (1) min (ssthresh, max(FlightSize, SMSS) + SMSS) or min (ssthresh, max(FlightSize, SMSS) + SMSS) or (2) ssthresh,
(2) ssthresh, where ssthresh is the value set when Fast where ssthresh is the value set when fast retransmit was entered,
Retransmit was entered, and where FlightSize in (1) is the amount and where FlightSize in (1) is the amount of data presently
of data presently outstanding. This is termed "deflating" the outstanding. This is termed "deflating" the window. If the
window. If the second option is selected, the implementation second option is selected, the implementation is encouraged to
is encouraged to take measures to avoid a possible burst of take measures to avoid a possible burst of data, in case the
data, in case the amount of data outstanding in the network is amount of data outstanding in the network is much less than the
much less than the new congestion window allows. A simple new congestion window allows. A simple mechanism is to limit the
mechanism is to limit the number of data packets that can be sent number of data packets that can be sent in response to a single
in response to a single acknowledgment. Exit the Fast Recovery acknowledgment. Exit the fast recovery procedure.
procedure.
Partial acknowledgments: Partial acknowledgments:
If this ACK does *not* acknowledge all of the data up to and If this ACK does *not* acknowledge all of the data up to and
including Recover, then this is a partial ACK. In this case, including recover, then this is a partial ACK. In this case,
retransmit the first unacknowledged segment. Deflate the retransmit the first unacknowledged segment. Deflate the
congestion window by the amount of new data acknowledged by the congestion window by the amount of new data acknowledged by the
cumulative acknowledgment field. If the partial ACK Cumulative Acknowledgment field. If the partial ACK acknowledges
acknowledges at least one SMSS of new data, then add back SMSS at least one SMSS of new data, then add back SMSS bytes to the
bytes to the congestion window. This artificially congestion window. This artificially inflates the congestion
inflates the congestion window in order to reflect the additional window in order to reflect the additional segment that has left
segment that has left the network. Send a new segment if the network. Send a new segment if permitted by the new value of
permitted by the new value of cwnd. This "partial window cwnd. This "partial window deflation" attempts to ensure that,
deflation" attempts to ensure that, when Fast Recovery eventually when fast recovery eventually ends, approximately ssthresh amount
ends, approximately ssthresh amount of data will be outstanding of data will be outstanding in the network. Do not exit the fast
in the network. Do not exit the Fast Recovery procedure (i.e., recovery procedure (i.e., if any duplicate ACKs subsequently
if any duplicate ACKs subsequently arrive, execute Step 4 of arrive, execute step 4 of Section 3.2 of [RFC5681]).
Section 3.2 of [RFC5681].
For the first partial ACK that arrives during Fast Recovery, also For the first partial ACK that arrives during fast recovery, also
reset the retransmit timer. Timer management is discussed in reset the retransmit timer. Timer management is discussed in
more detail in Section 4. more detail in Section 4.
4) Retransmit timeouts: 4) Retransmit timeouts:
After a retransmit timeout, record the highest sequence number After a retransmit timeout, record the highest sequence number
transmitted in the variable Recover and exit the Fast transmitted in the variable recover, and exit the fast recovery
Recovery procedure if applicable. procedure if applicable.
Step 2 above specifies a check that the Cumulative Acknowledgment Step 2 above specifies a check that the Cumulative Acknowledgment
field covers more than Recover. Because the acknowledgment field field covers more than recover. Because the acknowledgment field
contains the sequence number that the sender next expects to receive, contains the sequence number that the sender next expects to receive,
the acknowledgment "ack_number" covers more than Recover when: the acknowledgment "ack_number" covers more than recover when
ack_number - 1 > Recover; ack_number - 1 > recover;
i.e., at least one byte more of data is acknowledged beyond the i.e., at least one byte more of data is acknowledged beyond the
highest byte that was outstanding when Fast Retransmit was last highest byte that was outstanding when fast retransmit was last
entered. entered.
Note that in Step 3 above, the congestion window is deflated after Note that in step 3 above, the congestion window is deflated after a
a partial acknowledgment is received. The congestion window was partial acknowledgment is received. The congestion window was likely
likely to have been inflated considerably when the partial to have been inflated considerably when the partial acknowledgment
acknowledgment was received. In addition, depending on the original was received. In addition, depending on the original pattern of
pattern of packet losses, the partial acknowledgment might packet losses, the partial acknowledgment might acknowledge nearly a
acknowledge nearly a window of data. In this case, if the congestion window of data. In this case, if the congestion window was not
window was not deflated, the data sender might be able to send nearly deflated, the data sender might be able to send nearly a window of
a window of data back-to-back. data back-to-back.
This document does not specify the sender's response to duplicate This document does not specify the sender's response to duplicate
ACKs when the Fast Retransmit/Fast Recovery algorithm is not ACKs when the fast retransmit/fast recovery algorithm is not invoked.
invoked. This is addressed in other documents, such as those This is addressed in other documents, such as those describing the
describing the Limited Transmit procedure [RFC3042]. This document Limited Transmit procedure [RFC3042]. This document also does not
also does not address issues of adjusting the duplicate address issues of adjusting the duplicate acknowledgment threshold,
acknowledgment threshold, but assumes the threshold specified in but assumes the threshold specified in the IETF standards; the
the IETF standards; the current standard is [RFC5681], which current standard is [RFC5681], which specifies a threshold of three
specifies a threshold of three duplicate acknowledgments. duplicate acknowledgments.
As a final note, we would observe that in the absence of the SACK As a final note, we would observe that in the absence of the SACK
option, the data sender is working from limited information. When option, the data sender is working from limited information. When
the issue of recovery from multiple dropped packets from a single the issue of recovery from multiple dropped packets from a single
window of data is of particular importance, the best alternative window of data is of particular importance, the best alternative
would be to use the SACK option. would be to use the SACK option.
4. Handling Duplicate Acknowledgments After A Timeout 4. Handling Duplicate Acknowledgments after a Timeout
After each retransmit timeout, the highest sequence number After each retransmit timeout, the highest sequence number
transmitted so far is recorded in the variable "recover". transmitted so far is recorded in the variable recover. If, after a
If, after a retransmit timeout, the TCP data sender retransmits three retransmit timeout, the TCP data sender retransmits three consecutive
consecutive packets that have already been received by the data packets that have already been received by the data receiver, then
receiver, then the TCP data sender will receive three duplicate the TCP data sender will receive three duplicate acknowledgments that
acknowledgments that do not cover more than "recover". In this do not cover more than recover. In this case, the duplicate
case, the duplicate acknowledgments are not an indication of a new acknowledgments are not an indication of a new instance of
instance of congestion. They are simply an indication that the congestion. They are simply an indication that the sender has
sender has unnecessarily retransmitted at least three packets. unnecessarily retransmitted at least three packets.
However, when a retransmitted packet is itself dropped, the sender However, when a retransmitted packet is itself dropped, the sender
can also receive three duplicate acknowledgments that do not cover can also receive three duplicate acknowledgments that do not cover
more than "recover". In this case, the sender would have been more than recover. In this case, the sender would have been better
better off if it had initiated Fast Retransmit. For a TCP sender off if it had initiated fast retransmit. For a TCP sender that
that implements the algorithm specified in Section 3.2 of this implements the algorithm specified in Section 3.2 of this document,
document, the sender does not infer a packet drop from duplicate the sender does not infer a packet drop from duplicate
acknowledgments in this scenario. As always, the retransmit timer acknowledgments in this scenario. As always, the retransmit timer is
is the backup mechanism for inferring packet loss in this case. the backup mechanism for inferring packet loss in this case.
There are several heuristics, based on timestamps or on the amount of There are several heuristics, based on timestamps or on the amount of
advancement of the cumulative acknowledgment field, that allow the advancement of the Cumulative Acknowledgment field, that allow the
sender to distinguish, in some cases, between three duplicate sender to distinguish, in some cases, between three duplicate
acknowledgments following a retransmitted packet that was dropped, acknowledgments following a retransmitted packet that was dropped,
and three duplicate acknowledgments from the unnecessary and three duplicate acknowledgments from the unnecessary
retransmission of three packets [Gur03, GF04]. The TCP sender may retransmission of three packets [Gur03] [GF04]. The TCP sender may
use such a heuristic to decide to invoke a Fast Retransmit in some use such a heuristic to decide to invoke a fast retransmit in some
cases, even when the three duplicate acknowledgments do not cover cases, even when the three duplicate acknowledgments do not cover
more than "recover". more than recover.
For example, when three duplicate acknowledgments are caused by the For example, when three duplicate acknowledgments are caused by the
unnecessary retransmission of three packets, this is likely to be unnecessary retransmission of three packets, this is likely to be
accompanied by the cumulative acknowledgment field advancing by at accompanied by the Cumulative Acknowledgment field advancing by at
least four segments. Similarly, a heuristic based on timestamps uses least four segments. Similarly, a heuristic based on timestamps uses
the fact that when there is a hole in the sequence space, the the fact that when there is a hole in the sequence space, the
timestamp echoed in the duplicate acknowledgment is the timestamp of timestamp echoed in the duplicate acknowledgment is the timestamp of
the most recent data packet that advanced the cumulative the most recent data packet that advanced the Cumulative
acknowledgment field [RFC1323]. If timestamps are used, and the Acknowledgment field [RFC1323]. If timestamps are used, and the
sender stores the timestamp of the last acknowledged segment, then sender stores the timestamp of the last acknowledged segment, then
the timestamp echoed by duplicate acknowledgments can be used to the timestamp echoed by duplicate acknowledgments can be used to
distinguish between a retransmitted packet that was dropped and distinguish between a retransmitted packet that was dropped and three
three duplicate acknowledgments from the unnecessary duplicate acknowledgments from the unnecessary retransmission of
retransmission of three packets. three packets.
4.1. ACK Heuristic 4.1. ACK Heuristic
If the ACK-based heuristic is used, then following the advancement of If the ACK-based heuristic is used, then following the advancement of
the cumulative acknowledgment field, the sender stores the value of the Cumulative Acknowledgment field, the sender stores the value of
the previous cumulative acknowledgment as prev_highest_ack, and the previous cumulative acknowledgment as prev_highest_ack, and
stores the latest cumulative ACK as highest_ack. In addition, the stores the latest cumulative ACK as highest_ack. In addition, the
following check is performed if, in Step 2 of Section 3.2, the following check is performed if, in step 2 of Section 3.2, the
Cumulative Acknowledgment field does not cover more than "recover". Cumulative Acknowledgment field does not cover more than recover.
1*) If the Cumulative Acknowledgment field didn't cover more than 2*) If the Cumulative Acknowledgment field didn't cover more than
"recover", check to see if the congestion window is greater recover, check to see if the congestion window is greater than
than SMSS bytes and the difference between highest_ack and SMSS bytes and the difference between highest_ack and
prev_highest_ack is at most 4*SMSS bytes. If true, duplicate prev_highest_ack is at most 4*SMSS bytes. If true, duplicate
ACKs indicate a lost segment (enter Fast Retransmit). ACKs indicate a lost segment (enter fast retransmit).
Otherwise, duplicate ACKs likely result from unnecessary Otherwise, duplicate ACKs likely result from unnecessary
retransmissions (do not enter Fast Retransmit). retransmissions (do not enter fast retransmit).
The congestion window check serves to protect against fast retransmit The congestion window check serves to protect against fast retransmit
immediately after a retransmit timeout. immediately after a retransmit timeout.
If several ACKs are lost, the sender can see a jump in the cumulative If several ACKs are lost, the sender can see a jump in the cumulative
ACK of more than three segments, and the heuristic can fail. ACK of more than three segments, and the heuristic can fail.
[RFC5681] recommends that a receiver should [RFC5681] recommends that a receiver should send duplicate ACKs for
send duplicate ACKs for every out-of-order data packet, such as a every out-of-order data packet, such as a data packet received during
data packet received during Fast Recovery. The ACK heuristic is more fast recovery. The ACK heuristic is more likely to fail if the
likely to fail if the receiver does not follow this advice, because receiver does not follow this advice, because then a smaller number
then a smaller number of ACK losses are needed to produce a of ACK losses are needed to produce a sufficient jump in the
sufficient jump in the cumulative ACK. cumulative ACK.
4.2. Timestamp Heuristic 4.2. Timestamp Heuristic
If this heuristic is used, the sender stores the timestamp of the If this heuristic is used, the sender stores the timestamp of the
last acknowledged segment. In addition, the last sentence of step last acknowledged segment. In addition, the last sentence of step 2
2 in Section 3.2 is replaced as follows: in Section 3.2 of this document is replaced as follows:
1**) If the Cumulative Acknowledgment field didn't cover more than 2**) If the Cumulative Acknowledgment field didn't cover more than
"recover", check to see if the echoed timestamp in the last recover, check to see if the echoed timestamp in the last
non-duplicate acknowledgment equals the non-duplicate acknowledgment equals the stored timestamp. If
stored timestamp. If true, duplicate ACKs indicate a lost true, duplicate ACKs indicate a lost segment (enter fast
segment (enter Fast Retransmit). Otherwise, duplicate retransmit). Otherwise, duplicate ACKs likely result from
ACKs likely result from unnecessary retransmissions (do not unnecessary retransmissions (do not enter fast retransmit).
enter Fast Retransmit).
The timestamp heuristic works correctly, both when the receiver The timestamp heuristic works correctly, both when the receiver
echoes timestamps as specified by [RFC1323], and by its revision echoes timestamps, as specified by [RFC1323], and by its revision
attempts. However, if the receiver arbitrarily echoes timestamps, attempts. However, if the receiver arbitrarily echoes timestamps,
the heuristic can fail. The heuristic can also fail if a timeout was the heuristic can fail. The heuristic can also fail if a timeout was
spurious and returning ACKs are not from retransmitted segments. spurious and returning ACKs are not from retransmitted segments.
This can be prevented by detection algorithms such as [RFC3522]. This can be prevented by detection algorithms such as the Eifel
detection algorithm [RFC3522].
5. Implementation Issues for the Data Receiver 5. Implementation Issues for the Data Receiver
[RFC5681] specifies that "Out-of-order data segments SHOULD be [RFC5681] specifies that "Out-of-order data segments SHOULD be
acknowledged immediately, in order to accelerate loss recovery." acknowledged immediately, in order to accelerate loss recovery".
Neal Cardwell has noted that some data receivers do not send an Neal Cardwell has noted that some data receivers do not send an
immediate acknowledgment when they send a partial acknowledgment, immediate acknowledgment when they send a partial acknowledgment, but
but instead wait first for their delayed acknowledgment timer to instead wait first for their delayed acknowledgment timer to expire
expire [C98]. As [C98] notes, this severely limits the potential [C98]. As [C98] notes, this severely limits the potential benefit of
benefit of NewReno by delaying the receipt of the partial NewReno by delaying the receipt of the partial acknowledgment at the
acknowledgment at the data sender. Echoing [RFC5681], our data sender. Echoing [RFC5681], our recommendation is that the data
recommendation is that the data receiver send an immediate receiver send an immediate acknowledgment for an out-of-order
acknowledgment for an out-of-order segment, even when that segment, even when that out-of-order segment fills a hole in the
out-of-order segment fills a hole in the buffer. buffer.
6. Implementation Issues for the Data Sender 6. Implementation Issues for the Data Sender
In Section 3, Step 5 above, it is noted that implementations should In Section 3.2, step 3 above, it is noted that implementations should
take measures to avoid a possible burst of data when leaving Fast take measures to avoid a possible burst of data when leaving fast
Recovery, in case the amount of new data that the sender is eligible recovery, in case the amount of new data that the sender is eligible
to send due to the new value of the congestion window is large. This to send due to the new value of the congestion window is large. This
can arise during NewReno when ACKs are lost or treated as pure window can arise during NewReno when ACKs are lost or treated as pure window
updates, thereby causing the sender to underestimate the number of updates, thereby causing the sender to underestimate the number of
new segments that can be sent during the recovery procedure. new segments that can be sent during the recovery procedure.
Specifically, bursts can occur when the FlightSize is much less than Specifically, bursts can occur when the FlightSize is much less than
the new congestion window when exiting from Fast Recovery. One the new congestion window when exiting from fast recovery. One
simple mechanism to avoid a burst of data when leaving Fast Recovery simple mechanism to avoid a burst of data when leaving fast recovery
is to limit the number of data packets that can be sent in response is to limit the number of data packets that can be sent in response
to a single acknowledgment. (This is known as "maxburst_" in the ns to a single acknowledgment. (This is known as "maxburst_" in ns-2
simulator.) Other possible mechanisms for avoiding bursts include [NS].) Other possible mechanisms for avoiding bursts include rate-
rate-based pacing, or setting the slow-start threshold to the based pacing, or setting the slow start threshold to the resultant
resultant congestion window and then resetting the congestion window congestion window and then resetting the congestion window to
to FlightSize. A recommendation on the general mechanism to avoid FlightSize. A recommendation on the general mechanism to avoid
excessively bursty sending patterns is outside the scope of this excessively bursty sending patterns is outside the scope of this
document. document.
An implementation may want to use a separate flag to record whether An implementation may want to use a separate flag to record whether
or not it is presently in the Fast Recovery procedure. The use of or not it is presently in the fast recovery procedure. The use of
the value of the duplicate acknowledgment counter for this purpose is the value of the duplicate acknowledgment counter for this purpose is
not reliable because it can be reset upon window updates and not reliable, because it can be reset upon window updates and out-of-
out-of-order acknowledgments. order acknowledgments.
When updating the Cumulative Acknowledgment field outside of When updating the Cumulative Acknowledgment field outside of fast
Fast Recovery, the "recover" state variable may also need to be recovery, the state variable recover may also need to be updated in
updated in order to continue to permit possible entry into Fast order to continue to permit possible entry into fast recovery
Recovery (Section 3, step 1). This issue arises when an update (Section 3.2, step 2). This issue arises when an update of the
of the Cumulative Acknowledgment field results in a sequence Cumulative Acknowledgment field results in a sequence wraparound that
wraparound that affects the ordering between the Cumulative affects the ordering between the Cumulative Acknowledgment field and
Acknowledgment field and the "recover" state variable. Entry the state variable recover. Entry into fast recovery is only
into Fast Recovery is only possible when the Cumulative possible when the Cumulative Acknowledgment field covers more than
Acknowledgment field covers more than the "recover" state variable. the state variable recover.
It is important for the sender to respond correctly to duplicate ACKs It is important for the sender to respond correctly to duplicate ACKs
received when the sender is no longer in Fast Recovery (e.g., because received when the sender is no longer in fast recovery (e.g., because
of a Retransmit Timeout). The Limited Transmit procedure [RFC3042] of a retransmit timeout). The Limited Transmit procedure [RFC3042]
describes possible responses to the first and second duplicate describes possible responses to the first and second duplicate
acknowledgments. When three or more duplicate acknowledgments are acknowledgments. When three or more duplicate acknowledgments are
received, the Cumulative Acknowledgment field doesn't cover more received, the Cumulative Acknowledgment field doesn't cover more than
than "recover", and a new Fast Recovery is not invoked, it is recover, and a new fast recovery is not invoked, the sender should
important that the sender not execute the Fast Recovery steps (3) and follow the guidance in Section 4. Otherwise, the sender could end up
(4) in Section 3. Otherwise, the sender could end up in a chain of in a chain of spurious timeouts. We mention this only because
spurious timeouts. We mention this only because several NewReno several NewReno implementations had this bug, including the
implementations had this bug, including the implementation in the NS implementation in ns-2 [NS].
simulator.
It has been observed that some TCP implementations enter a slow start It has been observed that some TCP implementations enter a slow start
or congestion avoidance window updating algorithm immediately after or congestion avoidance window updating algorithm immediately after
the cwnd is set by the equation found in (Section 3, step 5), even the cwnd is set by the equation found in Section 3.2, step 3, even
without a new external event generating the cwnd change. Note that without a new external event generating the cwnd change. Note that
after cwnd is set based on the procedure for exiting Fast Recovery after cwnd is set based on the procedure for exiting fast recovery
(Section 3, step 5), cwnd should not be updated until a further (Section 3.2, step 3), cwnd should not be updated until a further
event occurs (e.g., arrival of an ack, or timeout) after this event occurs (e.g., arrival of an ack, or timeout) after this
adjustment. adjustment.
7. Security Considerations 7. Security Considerations
[RFC5681] discusses general security considerations concerning TCP [RFC5681] discusses general security considerations concerning TCP
congestion control. This document describes a specific algorithm congestion control. This document describes a specific algorithm
that conforms with the congestion control requirements of [RFC5681], that conforms with the congestion control requirements of [RFC5681],
and so those considerations apply to this algorithm, too. There are and so those considerations apply to this algorithm, too. There are
no known additional security concerns for this specific algorithm. no known additional security concerns for this specific algorithm.
8. IANA Considerations 8. Conclusions
This document has no actions for IANA.
9. Conclusions
This document specifies the NewReno Fast Retransmit and Fast Recovery This document specifies the NewReno fast retransmit and fast recovery
algorithms for TCP. This NewReno modification to TCP can even be algorithms for TCP. This NewReno modification to TCP can even be
important for TCP implementations that support the SACK option, important for TCP implementations that support the SACK option,
because the SACK option can only be used for TCP connections when because the SACK option can only be used for TCP connections when
both TCP end-nodes support the SACK option. NewReno performs better both TCP end-nodes support the SACK option. NewReno performs better
than Reno (RFC5681) in a number of scenarios discussed in than Reno in a number of scenarios discussed in previous versions of
previous versions of this RFC ([RFC2582], [RFC3782]). this RFC ([RFC2582] [RFC3782]).
A number of options to the basic algorithm presented in Section 3 are A number of options for the basic algorithms presented in Section 3
also referenced in Appendix A to this document. These include the are also referenced in Appendix A of this document. These include
handling of the retransmission timer, the response to partial the handling of the retransmission timer, the response to partial
acknowledgments, and whether or not the sender must maintain a state acknowledgments, and whether or not the sender must maintain a state
variable called Recover. Our belief is that the differences variable called recover. Our belief is that the differences between
between these variants of NewReno are small compared to the these variants of NewReno are small compared to the differences
differences between Reno and NewReno. That is, the important thing between Reno and NewReno. That is, the important thing is to
is to implement NewReno instead of Reno, for a TCP connection implement NewReno instead of Reno for a TCP connection without SACK;
without SACK; it is less important exactly which of the variants of it is less important exactly which variant of NewReno is implemented.
NewReno is implemented.
10. Acknowledgments 9. Acknowledgments
Many thanks to Anil Agarwal, Mark Allman, Armando Caro, Jeffrey Hsu, Many thanks to Anil Agarwal, Mark Allman, Armando Caro, Jeffrey Hsu,
Vern Paxson, Kacheong Poon, Keyur Shah, and Bernie Volz for detailed Vern Paxson, Kacheong Poon, Keyur Shah, and Bernie Volz for detailed
feedback on this document or on its precursor, RFC 2582. Jeffrey feedback on the precursor RFCs 2582 and 3782. Jeffrey Hsu provided
Hsu provided clarifications on the handling of the recover variable clarifications on the handling of the variable recover; these
that were applied to RFC 3782 as errata, and now are in Section 8 clarifications were applied to RFC 3782 via an erratum and are
of this document. Yoshifumi Nishida contributed a modification incorporated into the text of Section 6 of this document. Yoshifumi
to the fast recovery algorithm to account for the case in which Nishida contributed a modification to the fast recovery algorithm to
flightsize is 0 when the TCP sender leaves fast recovery, and the account for the case in which FlightSize is 0 when the TCP sender
TCP receiver uses delayed acknowledgments. Alexander Zimmermann leaves fast recovery and the TCP receiver uses delayed
provided several suggestions to improve the clarity of the document. acknowledgments. Alexander Zimmermann provided several suggestions
to improve the clarity of the document.
11. References 10. References
11.1. Normative References 10.1. 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.
[RFC5681] Allman, M., Paxson, V. and E. Blanton, "TCP Congestion [RFC5681] Allman, M., Paxson, V., and E. Blanton, "TCP Congestion
Control", RFC 5681, September 2009. Control", RFC 5681, September 2009.
11.2. Informative References 10.2. Informative References
[C98] Cardwell, N., "delayed ACKs for retransmitted packets: [C98] Cardwell, N., "delayed ACKs for retransmitted packets:
ouch!". November 1998, Email to the tcpimpl mailing list, ouch!". November 1998, Email to the tcpimpl mailing list,
Message-ID archived at
"Pine.LNX.4.02A.9811021421340.26785-100000@sake.cs. <http://groups.yahoo.com/group/tcp-impl/message/1428>.
washington.edu",
archived at "http://tcp-impl.lerc.nasa.gov/tcp-impl". [F94] Floyd, S., "TCP and Successive Fast Retransmits", Technical
report, May 1995.
<ftp://ftp.ee.lbl.gov/papers/fastretrans.ps>.
[FF96] Fall, K. and S. Floyd, "Simulation-based Comparisons of [FF96] Fall, K. and S. Floyd, "Simulation-based Comparisons of
Tahoe, Reno and SACK TCP", Computer Communication Review, Tahoe, Reno and SACK TCP", Computer Communication Review,
July 1996. July 1996. <ftp://ftp.ee.lbl.gov/papers/sacks.ps.Z>.
URL "ftp://ftp.ee.lbl.gov/papers/sacks.ps.Z".
[F94] Floyd, S., "TCP and Successive Fast Retransmits", Technical
report, October 1994. URL
"ftp://ftp.ee.lbl.gov/papers/fastretrans.ps".
[GF04] Gurtov, A. and S. Floyd, "Resolving Acknowledgment [GF04] Gurtov, A. and S. Floyd, "Resolving Acknowledgment
Ambiguity in non-SACK TCP", Next Generation Teletraffic and Ambiguity in non-SACK TCP", NExt Generation Teletraffic and
Wired/Wireless Advanced Networking (NEW2AN'04), February Wired/Wireless Advanced Networking (NEW2AN'04),
2004. URL "http://www.cs.helsinki.fi/u/gurtov/papers/ February 2004. <http://www.cs.helsinki.fi/u/gurtov/
heuristics.html". papers/heuristics.html>.
[Gur03] Gurtov, A., "[Tsvwg] resolving the problem of unnecessary [Gur03] Gurtov, A., "[Tsvwg] resolving the problem of unnecessary
fast retransmits in go-back-N", email to the tsvwg mailing fast retransmits in go-back-N", email to the tsvwg mailing
list, message ID <3F25B467.9020609@cs.helsinki.fi>, list, July 28, 2003. <http://www.ietf.org/mail-archive/
July 28, 2003. URL "http://www1.ietf.org/mail-archive/ web/tsvwg/current/msg04334.html>.
working-groups/tsvwg/current/msg04334.html".
[Hen98] Henderson, T., Re: NewReno and the 2001 Revision. September [Hen98] Henderson, T., "Re: NewReno and the 2001 Revision",
1998. Email to the tcpimpl mailing list, Message ID September 1998. Email to the tcpimpl mailing list,
"Pine.BSI.3.95.980923224136.26134A-100000@raptor.CS. archived at
Berkeley.EDU", <http://groups.yahoo.com/group/tcp-impl/message/1321>.
archived at "http://tcp-impl.lerc.nasa.gov/tcp-impl".
[Hoe95] Hoe, J., "Startup Dynamics of TCP's Congestion Control and [Hoe95] Hoe, J., "Startup Dynamics of TCP's Congestion Control and
Avoidance Schemes", Master's Thesis, MIT, 1995. Avoidance Schemes", Master's Thesis, MIT, June 1995.
[Hoe96] Hoe, J., "Improving the Start-up Behavior of a Congestion [Hoe96] Hoe, J., "Improving the Start-up Behavior of a Congestion
Control Scheme for TCP", ACM SIGCOMM, August 1996. URL Control Scheme for TCP", ACM SIGCOMM, August 1996.
"http://www.acm.org/sigcomm/sigcomm96/program.html". <http://ccr.sigcomm.org/archive/1996/conf/hoe.pdf>.
[LM97] Lin, D. and R. Morris, "Dynamics of Random Early [LM97] Lin, D. and R. Morris, "Dynamics of Random Early
Detection", SIGCOMM 97, September 1997. URL Detection", SIGCOMM 97, October 1997.
"http://www.acm.org/sigcomm/sigcomm97/program.html".
[NS] The Network Simulator (NS). [NS] "The Network Simulator version 2 (ns-2)",
URL "http://www.isi.edu/nsnam/ns/". <http://www.isi.edu/nsnam/ns/>.
[RFC1323] Jacobson, V., Braden, R. and D. Borman, "TCP Extensions for [RFC1323] Jacobson, V., Braden, R., and D. Borman, "TCP Extensions
High Performance", RFC 1323, May 1992. for High Performance", RFC 1323, May 1992.
[RFC2582] Floyd, S. and T. Henderson, "The NewReno Modification to [RFC2582] Floyd, S. and T. Henderson, "The NewReno Modification to
TCP's Fast Recovery Algorithm", RFC 2582, April 1999. TCP's Fast Recovery Algorithm", RFC 2582, April 1999.
[RFC2883] Floyd, S., J. Mahdavi, M. Mathis, and M. Podolsky, "The [RFC2883] Floyd, S., Mahdavi, J., Mathis, M., and M. Podolsky, "An
Selective Acknowledgment (SACK) Option for TCP, RFC 2883, Extension to the Selective Acknowledgement (SACK) Option
July 2000. for TCP", RFC 2883, July 2000.
[RFC3042] Allman, M., Balakrishnan, H. and S. Floyd, "Enhancing TCP's [RFC3042] Allman, M., Balakrishnan, H., and S. Floyd, "Enhancing
Loss Recovery Using Limited Transmit", RFC 3042, TCP's Loss Recovery Using Limited Transmit", RFC 3042,
January 2001. January 2001.
[RFC3522] Ludwig, R. and M. Meyer, "The Eifel Detection Algorithm for [RFC3522] Ludwig, R. and M. Meyer, "The Eifel Detection Algorithm for
TCP", RFC 3522, April 2003. TCP", RFC 3522, April 2003.
[RFC3782] Floyd, S., T. Henderson, and A. Gurtov, "The NewReno [RFC3782] Floyd, S., Henderson, T., and A. Gurtov, "The NewReno
Modification to TCP's Fast Recovery Algorithm", RFC 3782, Modification to TCP's Fast Recovery Algorithm", RFC 3782,
April 2004. April 2004.
Appendix A. Additional Information Appendix A. Additional Information
Previous versions of this RFC ([RFC2582], [RFC3782]) contained Previous versions of this RFC ([RFC2582] [RFC3782]) contained
additional informative material on the following subjects, and additional informative material on the following subjects, and may be
may be consulted by readers who may want more information about consulted by readers who may want more information about possible
possible variants to the algorithm and who may want references variants to the algorithms and who may want references to specific
to specific [NS] simulations that provide NewReno test cases. [NS] simulations that provide NewReno test cases.
Section 4 of [RFC3782] discusses some alternative behaviors for Section 4 of [RFC3782] discusses some alternative behaviors for
resetting the retransmit timer after a partial acknowledgment. resetting the retransmit timer after a partial acknowledgment.
Section 5 of [RFC3782] discusses some alternative behaviors for Section 5 of [RFC3782] discusses some alternative behaviors for
performing retransmission after a partial acknowledgment. performing retransmission after a partial acknowledgment.
Section 6 of [RFC3782] describes more information about the Section 6 of [RFC3782] describes more information about the
motivation for the sender's state variable Recover. motivation for the sender's state variable recover.
Section 9 of [RFC3782] introduces some NS simulation test Section 9 of [RFC3782] introduces some NS simulation test suites for
suites for NewReno. In addition, references to simulation NewReno. In addition, references to simulation results can be found
results can be found throughout [RFC3782]. throughout [RFC3782].
Section 10 of [RFC3782] provides a comparison of Reno and Section 10 of [RFC3782] provides a comparison of Reno and
NewReno TCP. NewReno TCP.
Section 11 of [RFC3782] listed changes relative to [RFC2582]. Section 11 of [RFC3782] lists changes relative to [RFC2582].
Appendix B. Changes Relative to RFC 3782 Appendix B. Changes Relative to RFC 3782
In [RFC3782], the cwnd after Full ACK reception will be set to In [RFC3782], the cwnd after Full ACK reception will be set to
(1) min (ssthresh, FlightSize + SMSS) or (2) ssthresh. However, (1) min (ssthresh, FlightSize + SMSS) or (2) ssthresh. However, the
there is a risk in the first option which results in performance first option carries a risk of performance degradation: With the
degradation. With the first option, if FlightSize is zero, the first option, if FlightSize is zero, the result will be 1 SMSS. This
result will be 1 SMSS. This means TCP can transmit only 1 segment means TCP can transmit only 1 segment at that moment, which can cause
at this moment, which can cause delay in ACK transmission at receiver a delay in ACK transmission at the receiver due to a delayed ACK
due to delayed ACK algorithm. algorithm.
The FlightSize on Full ACK reception can be zero in some situations. The FlightSize on Full ACK reception can be zero in some situations.
A typical example is where sending window size during fast recovery A typical example is where the sending window size during fast
is small. In this case, the retransmitted packet and new data packets recovery is small. In this case, the retransmitted packet and new
can be transmitted within a short interval. If all these packets data packets can be transmitted within a short interval. If all
successfully arrive, the receiver may generate a Full ACK that these packets successfully arrive, the receiver may generate a Full
acknowledges all outstanding data. Even if window size is not small, ACK that acknowledges all outstanding data. Even if the window size
loss of ACK packets or receive buffer shortage during fast recovery is not small, loss of ACK packets or a receive buffer shortage during
can also increase the possibility of falling into this situation. fast recovery can also increase the possibility of falling into this
situation.
The proposed fix in this document, which sets cwnd to at least 2*SMSS The proposed fix in this document, which sets cwnd to at least 2*SMSS
if the implementation uses option 1 in the Full ACK case (Section 3.2 if the implementation uses option 1 in the Full ACK case
step 3, option 1), ensures that the sender TCP transmits at least two (Section 3.2, step 3, option 1), ensures that the sender TCP
segments on Full ACK reception. transmits at least two segments on Full ACK reception.
In addition, errata for RFC3782 (editorial clarification to Section 8 In addition, an erratum was reported for RFC 3782 (an editorial
of RFC2582, which is now Section 6 of this document) has been clarification to Section 8); this erratum has been addressed in
applied. Section 6 of this document.
The specification text (Section 3.2 herein) was rewritten to more The specification text (Section 3.2 herein) was rewritten to more
closely track Section 3.2 of [RFC5681]. closely track Section 3.2 of [RFC5681].
Sections 4, 5, 9-11 of [RFC3782] were removed, and instead Appendix Sections 4, 5, and 9-11 of [RFC3782] were removed, and instead
A of this document was added to back-reference this informative Appendix A of this document was added to back-reference this
material. A few references that have no citation in the main body informative material. A few references that have no citation in the
of the draft have been removed. main body of the document have been removed.
Appendix C. Document Revision History
To be removed upon publication
+----------+--------------------------------------------------+
| Revision | Comments |
+----------+--------------------------------------------------+
| draft-00 | RFC3782 errata applied, and changes applied from |
| | draft-nishida-newreno-modification-02 |
+----------+--------------------------------------------------+
| draft-01 | Non-normative sections moved to appendices, |
| | editorial clarifications applied as suggested |
| | by Alexander Zimmermann. |
+----------+--------------------------------------------------+
| draft-02 | Better align specification text with RFC5681. |
| | Replace informative appendices by a new appendix |
| | that just provides back-references to earlier |
| | NewReno RFCs. |
+----------+--------------------------------------------------+
| draft-03 | Document refresh and fix id-nits |
+----------+--------------------------------------------------+
| draft-04 | Address editorial comments received from secdir |
| | review (provided by Tom Yu). |
+----------+--------------------------------------------------+
| draft-05 | Address IESG review comments from David |
| | Harrington, and Gen-ART review comments from |
| | Ben Campbell. |
+----------+--------------------------------------------------+
Authors' Addresses Authors' Addresses
Tom Henderson Tom Henderson
The Boeing Company The Boeing Company
EMail: thomas.r.henderson@boeing.com EMail: thomas.r.henderson@boeing.com
Sally Floyd Sally Floyd
International Computer Science Institute International Computer Science Institute
skipping to change at page 15, line 43 skipping to change at page 16, line 34
Finland Finland
EMail: gurtov@ee.oulu.fi EMail: gurtov@ee.oulu.fi
Yoshifumi Nishida Yoshifumi Nishida
WIDE Project WIDE Project
Endo 5322 Endo 5322
Fujisawa, Kanagawa 252-8520 Fujisawa, Kanagawa 252-8520
Japan Japan
Email: nishida@wide.ad.jp EMail: nishida@wide.ad.jp
 End of changes. 107 change blocks. 
377 lines changed or deleted 333 lines changed or added

This html diff was produced by rfcdiff 1.41. The latest version is available from http://tools.ietf.org/tools/rfcdiff/