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rfc:rfc2581

Network Working Group M. Allman Request for Comments: 2581 NASA Glenn/Sterling Software Obsoletes: 2001 V. Paxson Category: Standards Track ACIRI / ICSI

                                                            W. Stevens
                                                            Consultant
                                                            April 1999
                       TCP Congestion Control

Status of this Memo

 This document specifies an Internet standards track protocol for the
 Internet community, and requests discussion and suggestions for
 improvements.  Please refer to the current edition of the "Internet
 Official Protocol Standards" (STD 1) for the standardization state
 and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

 Copyright (C) The Internet Society (1999).  All Rights Reserved.

Abstract

 This document defines TCP's four intertwined congestion control
 algorithms: slow start, congestion avoidance, fast retransmit, and
 fast recovery.  In addition, the document specifies how TCP should
 begin transmission after a relatively long idle period, as well as
 discussing various acknowledgment generation methods.

1. Introduction

 This document specifies four TCP [Pos81] congestion control
 algorithms: slow start, congestion avoidance, fast retransmit and
 fast recovery.  These algorithms were devised in [Jac88] and [Jac90].
 Their use with TCP is standardized in [Bra89].
 This document is an update of [Ste97].  In addition to specifying the
 congestion control algorithms, this document specifies what TCP
 connections should do after a relatively long idle period, as well as
 specifying and clarifying some of the issues pertaining to TCP ACK
 generation.
 Note that [Ste94] provides examples of these algorithms in action and
 [WS95] provides an explanation of the source code for the BSD
 implementation of these algorithms.

Allman, et. al. Standards Track [Page 1] RFC 2581 TCP Congestion Control April 1999

 This document is organized as follows.  Section 2 provides various
 definitions which will be used throughout the document.  Section 3
 provides a specification of the congestion control algorithms.
 Section 4 outlines concerns related to the congestion control
 algorithms and finally, section 5 outlines security considerations.
 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
 document are to be interpreted as described in [Bra97].

2. Definitions

 This section provides the definition of several terms that will be
 used throughout the remainder of this document.
 SEGMENT:
    A segment is ANY TCP/IP data or acknowledgment packet (or both).
 SENDER MAXIMUM SEGMENT SIZE (SMSS):  The SMSS is the size of the
    largest segment that the sender can transmit.  This value can be
    based on the maximum transmission unit of the network, the path
    MTU discovery [MD90] algorithm, RMSS (see next item), or other
    factors.  The size does not include the TCP/IP headers and
    options.
 RECEIVER MAXIMUM SEGMENT SIZE (RMSS):  The RMSS is the size of the
    largest segment the receiver is willing to accept.  This is the
    value specified in the MSS option sent by the receiver during
    connection startup.  Or, if the MSS option is not used, 536 bytes
    [Bra89].  The size does not include the TCP/IP headers and
    options.
 FULL-SIZED SEGMENT: A segment that contains the maximum number of
    data bytes permitted (i.e., a segment containing SMSS bytes of
    data).
 RECEIVER WINDOW (rwnd) The most recently advertised receiver window.
 CONGESTION WINDOW (cwnd):  A TCP state variable that limits the
    amount of data a TCP can send.  At any given time, a TCP MUST NOT
    send data with a sequence number higher than the sum of the
    highest acknowledged sequence number and the minimum of cwnd and
    rwnd.
 INITIAL WINDOW (IW):  The initial window is the size of the sender's
    congestion window after the three-way handshake is completed.

Allman, et. al. Standards Track [Page 2] RFC 2581 TCP Congestion Control April 1999

 LOSS WINDOW (LW):  The loss window is the size of the congestion
    window after a TCP sender detects loss using its retransmission
    timer.
 RESTART WINDOW (RW):  The restart window is the size of the
    congestion window after a TCP restarts transmission after an idle
    period (if the slow start algorithm is used; see section 4.1 for
    more discussion).
 FLIGHT SIZE:  The amount of data that has been sent but not yet
    acknowledged.

3. Congestion Control Algorithms

 This section defines the four congestion control algorithms: slow
 start, congestion avoidance, fast retransmit and fast recovery,
 developed in [Jac88] and [Jac90].  In some situations it may be
 beneficial for a TCP sender to be more conservative than the
 algorithms allow, however a TCP MUST NOT be more aggressive than the
 following algorithms allow (that is, MUST NOT send data when the
 value of cwnd computed by the following algorithms would not allow
 the data to be sent).

3.1 Slow Start and Congestion Avoidance

 The slow start and congestion avoidance algorithms MUST be used by a
 TCP sender to control the amount of outstanding data being injected
 into the network.  To implement these algorithms, two variables are
 added to the TCP per-connection state.  The congestion window (cwnd)
 is a sender-side limit on the amount of data the sender can transmit
 into the network before receiving an acknowledgment (ACK), while the
 receiver's advertised window (rwnd) is a receiver-side limit on the
 amount of outstanding data.  The minimum of cwnd and rwnd governs
 data transmission.
 Another state variable, the slow start threshold (ssthresh), is used
 to determine whether the slow start or congestion avoidance algorithm
 is used to control data transmission, as discussed below.
 Beginning transmission into a network with unknown conditions
 requires TCP to slowly probe the network to determine the available
 capacity, in order to avoid congesting the network with an
 inappropriately large burst of data.  The slow start algorithm is
 used for this purpose at the beginning of a transfer, or after
 repairing loss detected by the retransmission timer.

Allman, et. al. Standards Track [Page 3] RFC 2581 TCP Congestion Control April 1999

 IW, the initial value of cwnd, MUST be less than or equal to 2*SMSS
 bytes and MUST NOT be more than 2 segments.
 We note that a non-standard, experimental TCP extension allows that a
 TCP MAY use a larger initial window (IW), as defined in equation 1
 [AFP98]:
    IW = min (4*SMSS, max (2*SMSS, 4380 bytes))           (1)
 With this extension, a TCP sender MAY use a 3 or 4 segment initial
 window, provided the combined size of the segments does not exceed
 4380 bytes.  We do NOT allow this change as part of the standard
 defined by this document.  However, we include discussion of (1) in
 the remainder of this document as a guideline for those experimenting
 with the change, rather than conforming to the present standards for
 TCP congestion control.
 The initial value of ssthresh MAY be arbitrarily high (for example,
 some implementations use the size of the advertised window), but it
 may be reduced in response to congestion.  The slow start algorithm
 is used when cwnd < ssthresh, while the congestion avoidance
 algorithm is used when cwnd > ssthresh.  When cwnd and ssthresh are
 equal the sender may use either slow start or congestion avoidance.
 During slow start, a TCP increments cwnd by at most SMSS bytes for
 each ACK received that acknowledges new data.  Slow start ends when
 cwnd exceeds ssthresh (or, optionally, when it reaches it, as noted
 above) or when congestion is observed.
 During congestion avoidance, cwnd is incremented by 1 full-sized
 segment per round-trip time (RTT).  Congestion avoidance continues
 until congestion is detected.  One formula commonly used to update
 cwnd during congestion avoidance is given in equation 2:
    cwnd += SMSS*SMSS/cwnd                     (2)
 This adjustment is executed on every incoming non-duplicate ACK.
 Equation (2) provides an acceptable approximation to the underlying
 principle of increasing cwnd by 1 full-sized segment per RTT.  (Note
 that for a connection in which the receiver acknowledges every data
 segment, (2) proves slightly more aggressive than 1 segment per RTT,
 and for a receiver acknowledging every-other packet, (2) is less
 aggressive.)

Allman, et. al. Standards Track [Page 4] RFC 2581 TCP Congestion Control April 1999

 Implementation Note: Since integer arithmetic is usually used in TCP
 implementations, the formula given in equation 2 can fail to increase
 cwnd when the congestion window is very large (larger than
 SMSS*SMSS).  If the above formula yields 0, the result SHOULD be
 rounded up to 1 byte.
 Implementation Note: older implementations have an additional
 additive constant on the right-hand side of equation (2).  This is
 incorrect and can actually lead to diminished performance [PAD+98].
 Another acceptable way to increase cwnd during congestion avoidance
 is to count the number of bytes that have been acknowledged by ACKs
 for new data.  (A drawback of this implementation is that it requires
 maintaining an additional state variable.)  When the number of bytes
 acknowledged reaches cwnd, then cwnd can be incremented by up to SMSS
 bytes.  Note that during congestion avoidance, cwnd MUST NOT be
 increased by more than the larger of either 1 full-sized segment per
 RTT, or the value computed using equation 2.
 Implementation Note: some implementations maintain cwnd in units of
 bytes, while others in units of full-sized segments.  The latter will
 find equation (2) difficult to use, and may prefer to use the
 counting approach discussed in the previous paragraph.
 When a TCP sender detects segment loss using the retransmission
 timer, the value of ssthresh MUST be set to no more than the value
 given in equation 3:
    ssthresh = max (FlightSize / 2, 2*SMSS)            (3)
 As discussed above, FlightSize is the amount of outstanding data in
 the network.
 Implementation Note: an easy mistake to make is to simply use cwnd,
 rather than FlightSize, which in some implementations may
 incidentally increase well beyond rwnd.
 Furthermore, upon a timeout cwnd MUST be set to no more than the loss
 window, LW, which equals 1 full-sized segment (regardless of the
 value of IW).  Therefore, after retransmitting the dropped segment
 the TCP sender uses the slow start algorithm to increase the window
 from 1 full-sized segment to the new value of ssthresh, at which
 point congestion avoidance again takes over.

Allman, et. al. Standards Track [Page 5] RFC 2581 TCP Congestion Control April 1999

3.2 Fast Retransmit/Fast Recovery

 A TCP receiver SHOULD send an immediate duplicate ACK when an out-
 of-order segment arrives.  The purpose of this ACK is to inform the
 sender that a segment was received out-of-order and which sequence
 number is expected.  From the sender's perspective, duplicate ACKs
 can be caused by a number of network problems.  First, they can be
 caused by dropped segments.  In this case, all segments after the
 dropped segment will trigger duplicate ACKs.  Second, duplicate ACKs
 can be caused by the re-ordering of data segments by the network (not
 a rare event along some network paths [Pax97]).  Finally, duplicate
 ACKs can be caused by replication of ACK or data segments by the
 network.  In addition, a TCP receiver SHOULD send an immediate ACK
 when the incoming segment fills in all or part of a gap in the
 sequence space.  This will generate more timely information for a
 sender recovering from a loss through a retransmission timeout, a
 fast retransmit, or an experimental loss recovery algorithm, such as
 NewReno [FH98].
 The TCP sender SHOULD use the "fast retransmit" algorithm to detect
 and repair loss, based on incoming duplicate ACKs.  The fast
 retransmit algorithm uses the arrival of 3 duplicate ACKs (4
 identical ACKs without the arrival of any other intervening packets)
 as an indication that a segment has been lost.  After receiving 3
 duplicate ACKs, TCP performs a retransmission of what appears to be
 the missing segment, without waiting for the retransmission timer to
 expire.
 After the fast retransmit algorithm sends what appears to be the
 missing segment, the "fast recovery" algorithm governs the
 transmission of new data until a non-duplicate ACK arrives.  The
 reason for not performing slow start is that the receipt of the
 duplicate ACKs not only indicates that a segment has been lost, but
 also that segments are most likely leaving the network (although a
 massive segment duplication by the network can invalidate this
 conclusion).  In other words, since the receiver can only generate a
 duplicate ACK when a segment has arrived, that segment has left the
 network and is in the receiver's buffer, so we know it is no longer
 consuming network resources.  Furthermore, since the ACK "clock"
 [Jac88] is preserved, the TCP sender can continue to transmit new
 segments (although transmission must continue using a reduced cwnd).
 The fast retransmit and fast recovery algorithms are usually
 implemented together as follows.
 1.  When the third duplicate ACK is received, set ssthresh to no more
     than the value given in equation 3.

Allman, et. al. Standards Track [Page 6] RFC 2581 TCP Congestion Control April 1999

 2.  Retransmit the lost segment and set cwnd to ssthresh plus 3*SMSS.
     This artificially "inflates" the congestion window by the number
     of segments (three) that have left the network and which the
     receiver has buffered.
 3.  For each additional duplicate ACK received, increment cwnd by
     SMSS.  This artificially inflates the congestion window in order
     to reflect the additional segment that has left the network.
 4.  Transmit a segment, if allowed by the new value of cwnd and the
     receiver's advertised window.
 5.  When the next ACK arrives that acknowledges new data, set cwnd to
     ssthresh (the value set in step 1).  This is termed "deflating"
     the window.
     This ACK should be the acknowledgment elicited by the
     retransmission from step 1, one RTT after the retransmission
     (though it may arrive sooner in the presence of significant out-
     of-order delivery of data segments at the receiver).
     Additionally, this ACK should acknowledge all the intermediate
     segments sent between the lost segment and the receipt of the
     third duplicate ACK, if none of these were lost.
 Note: This algorithm is known to generally not recover very
 efficiently from multiple losses in a single flight of packets
 [FF96].  One proposed set of modifications to address this problem
 can be found in [FH98].

4. Additional Considerations

4.1 Re-starting Idle Connections

 A known problem with the TCP congestion control algorithms described
 above is that they allow a potentially inappropriate burst of traffic
 to be transmitted after TCP has been idle for a relatively long
 period of time.  After an idle period, TCP cannot use the ACK clock
 to strobe new segments into the network, as all the ACKs have drained
 from the network.  Therefore, as specified above, TCP can potentially
 send a cwnd-size line-rate burst into the network after an idle
 period.
 [Jac88] recommends that a TCP use slow start to restart transmission
 after a relatively long idle period.  Slow start serves to restart
 the ACK clock, just as it does at the beginning of a transfer.  This
 mechanism has been widely deployed in the following manner.  When TCP
 has not received a segment for more than one retransmission timeout,
 cwnd is reduced to the value of the restart window (RW) before

Allman, et. al. Standards Track [Page 7] RFC 2581 TCP Congestion Control April 1999

 transmission begins.
 For the purposes of this standard, we define RW = IW.
 We note that the non-standard experimental extension to TCP defined
 in [AFP98] defines RW = min(IW, cwnd), with the definition of IW
 adjusted per equation (1) above.
 Using the last time a segment was received to determine whether or
 not to decrease cwnd fails to deflate cwnd in the common case of
 persistent HTTP connections [HTH98].  In this case, a WWW server
 receives a request before transmitting data to the WWW browser.  The
 reception of the request makes the test for an idle connection fail,
 and allows the TCP to begin transmission with a possibly
 inappropriately large cwnd.
 Therefore, a TCP SHOULD set cwnd to no more than RW before beginning
 transmission if the TCP has not sent data in an interval exceeding
 the retransmission timeout.

4.2 Generating Acknowledgments

 The delayed ACK algorithm specified in [Bra89] SHOULD be used by a
 TCP receiver.  When used, a TCP receiver MUST NOT excessively delay
 acknowledgments.  Specifically, an ACK SHOULD be generated for at
 least every second full-sized segment, and MUST be generated within
 500 ms of the arrival of the first unacknowledged packet.
 The requirement that an ACK "SHOULD" be generated for at least every
 second full-sized segment is listed in [Bra89] in one place as a
 SHOULD and another as a MUST.  Here we unambiguously state it is a
 SHOULD.  We also emphasize that this is a SHOULD, meaning that an
 implementor should indeed only deviate from this requirement after
 careful consideration of the implications.  See the discussion of
 "Stretch ACK violation" in [PAD+98] and the references therein for a
 discussion of the possible performance problems with generating ACKs
 less frequently than every second full-sized segment.
 In some cases, the sender and receiver may not agree on what
 constitutes a full-sized segment.  An implementation is deemed to
 comply with this requirement if it sends at least one acknowledgment
 every time it receives 2*RMSS bytes of new data from the sender,
 where RMSS is the Maximum Segment Size specified by the receiver to
 the sender (or the default value of 536 bytes, per [Bra89], if the
 receiver does not specify an MSS option during connection
 establishment).  The sender may be forced to use a segment size less
 than RMSS due to the maximum transmission unit (MTU), the path MTU
 discovery algorithm or other factors.  For instance, consider the

Allman, et. al. Standards Track [Page 8] RFC 2581 TCP Congestion Control April 1999

 case when the receiver announces an RMSS of X bytes but the sender
 ends up using a segment size of Y bytes (Y < X) due to path MTU
 discovery (or the sender's MTU size).  The receiver will generate
 stretch ACKs if it waits for 2*X bytes to arrive before an ACK is
 sent.  Clearly this will take more than 2 segments of size Y bytes.
 Therefore, while a specific algorithm is not defined, it is desirable
 for receivers to attempt to prevent this situation, for example by
 acknowledging at least every second segment, regardless of size.
 Finally, we repeat that an ACK MUST NOT be delayed for more than 500
 ms waiting on a second full-sized segment to arrive.
 Out-of-order data segments SHOULD be acknowledged immediately, in
 order to accelerate loss recovery.  To trigger the fast retransmit
 algorithm, the receiver SHOULD send an immediate duplicate ACK when
 it receives a data segment above a gap in the sequence space.  To
 provide feedback to senders recovering from losses, the receiver
 SHOULD send an immediate ACK when it receives a data segment that
 fills in all or part of a gap in the sequence space.
 A TCP receiver MUST NOT generate more than one ACK for every incoming
 segment, other than to update the offered window as the receiving
 application consumes new data [page 42, Pos81][Cla82].

4.3 Loss Recovery Mechanisms

 A number of loss recovery algorithms that augment fast retransmit and
 fast recovery have been suggested by TCP researchers.  While some of
 these algorithms are based on the TCP selective acknowledgment (SACK)
 option [MMFR96], such as [FF96,MM96a,MM96b], others do not require
 SACKs [Hoe96,FF96,FH98].  The non-SACK algorithms use "partial
 acknowledgments" (ACKs which cover new data, but not all the data
 outstanding when loss was detected) to trigger retransmissions.
 While this document does not standardize any of the specific
 algorithms that may improve fast retransmit/fast recovery, these
 enhanced algorithms are implicitly allowed, as long as they follow
 the general principles of the basic four algorithms outlined above.
 Therefore, when the first loss in a window of data is detected,
 ssthresh MUST be set to no more than the value given by equation (3).
 Second, until all lost segments in the window of data in question are
 repaired, the number of segments transmitted in each RTT MUST be no
 more than half the number of outstanding segments when the loss was
 detected.  Finally, after all loss in the given window of segments
 has been successfully retransmitted, cwnd MUST be set to no more than
 ssthresh and congestion avoidance MUST be used to further increase
 cwnd.  Loss in two successive windows of data, or the loss of a
 retransmission, should be taken as two indications of congestion and,
 therefore, cwnd (and ssthresh) MUST be lowered twice in this case.

Allman, et. al. Standards Track [Page 9] RFC 2581 TCP Congestion Control April 1999

 The algorithms outlined in [Hoe96,FF96,MM96a,MM6b] follow the
 principles of the basic four congestion control algorithms outlined
 in this document.

5. Security Considerations

 This document requires a TCP to diminish its sending rate in the
 presence of retransmission timeouts and the arrival of duplicate
 acknowledgments.  An attacker can therefore impair the performance of
 a TCP connection by either causing data packets or their
 acknowledgments to be lost, or by forging excessive duplicate
 acknowledgments.  Causing two congestion control events back-to-back
 will often cut ssthresh to its minimum value of 2*SMSS, causing the
 connection to immediately enter the slower-performing congestion
 avoidance phase.
 The Internet to a considerable degree relies on the correct
 implementation of these algorithms in order to preserve network
 stability and avoid congestion collapse.  An attacker could cause TCP
 endpoints to respond more aggressively in the face of congestion by
 forging excessive duplicate acknowledgments or excessive
 acknowledgments for new data.  Conceivably, such an attack could
 drive a portion of the network into congestion collapse.

6. Changes Relative to RFC 2001

 This document has been extensively rewritten editorially and it is
 not feasible to itemize the list of changes between the two
 documents. The intention of this document is not to change any of the
 recommendations given in RFC 2001, but to further clarify cases that
 were not discussed in detail in 2001. Specifically, this document
 suggests what TCP connections should do after a relatively long idle
 period, as well as specifying and clarifying some of the issues
 pertaining to TCP ACK generation.  Finally, the allowable upper bound
 for the initial congestion window has also been raised from one to
 two segments.

Acknowledgments

 The four algorithms that are described were developed by Van
 Jacobson.
 Some of the text from this document is taken from "TCP/IP
 Illustrated, Volume 1: The Protocols" by W. Richard Stevens
 (Addison-Wesley, 1994) and "TCP/IP Illustrated, Volume 2: The
 Implementation" by Gary R. Wright and W.  Richard Stevens (Addison-
 Wesley, 1995).  This material is used with the permission of
 Addison-Wesley.

Allman, et. al. Standards Track [Page 10] RFC 2581 TCP Congestion Control April 1999

 Neal Cardwell, Sally Floyd, Craig Partridge and Joe Touch contributed
 a number of helpful suggestions.

References

 [AFP98]  Allman, M., Floyd, S. and C. Partridge, "Increasing TCP's
          Initial Window Size, RFC 2414, September 1998.
 [Bra89]  Braden, R., "Requirements for Internet Hosts --
          Communication Layers", STD 3, RFC 1122, October 1989.
 [Bra97]  Bradner, S., "Key words for use in RFCs to Indicate
          Requirement Levels", BCP 14, RFC 2119, March 1997.
 [Cla82]  Clark, D., "Window and Acknowledgment Strategy in TCP", RFC
          813, July 1982.
 [FF96]   Fall, K. and S. Floyd, "Simulation-based Comparisons of
          Tahoe, Reno and SACK TCP", Computer Communication Review,
          July 1996. ftp://ftp.ee.lbl.gov/papers/sacks.ps.Z.
 [FH98]   Floyd, S. and T. Henderson, "The NewReno Modification to
          TCP's Fast Recovery Algorithm", RFC 2582, April 1999.
 [Flo94]  Floyd, S., "TCP and Successive Fast Retransmits. Technical
          report", October 1994.
          ftp://ftp.ee.lbl.gov/papers/fastretrans.ps.
 [Hoe96]  Hoe, J., "Improving the Start-up Behavior of a Congestion
          Control Scheme for TCP", In ACM SIGCOMM, August 1996.
 [HTH98]  Hughes, A., Touch, J. and J. Heidemann, "Issues in TCP
          Slow-Start Restart After Idle", Work in Progress.
 [Jac88]  Jacobson, V., "Congestion Avoidance and Control", Computer
          Communication Review, vol. 18, no. 4, pp. 314-329, Aug.
          1988.  ftp://ftp.ee.lbl.gov/papers/congavoid.ps.Z.
 [Jac90]  Jacobson, V., "Modified TCP Congestion Avoidance Algorithm",
          end2end-interest mailing list, April 30, 1990.
          ftp://ftp.isi.edu/end2end/end2end-interest-1990.mail.
 [MD90]   Mogul, J. and S. Deering, "Path MTU Discovery", RFC 1191,
          November 1990.

Allman, et. al. Standards Track [Page 11] RFC 2581 TCP Congestion Control April 1999

 [MM96a]  Mathis, M. and J. Mahdavi, "Forward Acknowledgment: Refining
          TCP Congestion Control", Proceedings of SIGCOMM'96, August,
          1996, Stanford, CA.  Available
          fromhttp://www.psc.edu/networking/papers/papers.html
 [MM96b]  Mathis, M. and J. Mahdavi, "TCP Rate-Halving with Bounding
          Parameters", Technical report.  Available from
          http://www.psc.edu/networking/papers/FACKnotes/current.
 [MMFR96] Mathis, M., Mahdavi, J., Floyd, S. and A. Romanow, "TCP
          Selective Acknowledgement Options", RFC 2018, October 1996.
 [PAD+98] Paxson, V., Allman, M., Dawson, S., Fenner, W., Griner, J.,
          Heavens, I., Lahey, K., Semke, J. and B. Volz, "Known TCP
          Implementation Problems", RFC 2525, March 1999.
 [Pax97]  Paxson, V., "End-to-End Internet Packet Dynamics",
          Proceedings of SIGCOMM '97, Cannes, France, Sep. 1997.
 [Pos81]  Postel, J., "Transmission Control Protocol", STD 7, RFC 793,
          September 1981.
 [Ste94]  Stevens, W., "TCP/IP Illustrated, Volume 1: The Protocols",
          Addison-Wesley, 1994.
 [Ste97]  Stevens, W., "TCP Slow Start, Congestion Avoidance, Fast
          Retransmit, and Fast Recovery Algorithms", RFC 2001, January
          1997.
 [WS95]   Wright, G. and W. Stevens, "TCP/IP Illustrated, Volume 2:
          The Implementation", Addison-Wesley, 1995.

Allman, et. al. Standards Track [Page 12] RFC 2581 TCP Congestion Control April 1999

Authors' Addresses

 Mark Allman
 NASA Glenn Research Center/Sterling Software
 Lewis Field
 21000 Brookpark Rd.  MS 54-2
 Cleveland, OH  44135
 216-433-6586
 EMail: mallman@grc.nasa.gov
 http://roland.grc.nasa.gov/~mallman
 Vern Paxson
 ACIRI / ICSI
 1947 Center Street
 Suite 600
 Berkeley, CA 94704-1198
 Phone: +1 510/642-4274 x302
 EMail: vern@aciri.org
 W. Richard Stevens
 1202 E. Paseo del Zorro
 Tucson, AZ  85718
 520-297-9416
 EMail: rstevens@kohala.com
 http://www.kohala.com/~rstevens

Allman, et. al. Standards Track [Page 13] RFC 2581 TCP Congestion Control April 1999

Full Copyright Statement

 Copyright (C) The Internet Society (1999).  All Rights Reserved.
 This document and translations of it may be copied and furnished to
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 or assist in its implementation may be prepared, copied, published
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 kind, provided that the above copyright notice and this paragraph are
 included on all such copies and derivative works.  However, this
 document itself may not be modified in any way, such as by removing
 the copyright notice or references to the Internet Society or other
 Internet organizations, except as needed for the purpose of
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 The limited permissions granted above are perpetual and will not be
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 This document and the information contained herein is provided on an
 "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
 TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
 BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
 MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Allman, et. al. Standards Track [Page 14]

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