TCP Performance Implications of Network Path Asymmetry
draft-ietf-pilc-asym-08

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        BCP 69
        RFC 3449
                                      
        Title:      TCP Performance Implications of Network Path
                    Asymmetry
        Author(s):  H. Balakrishnan, V. Padmanabhan, G. Fairhurst,
                    M. Sooriyabandara
        Status:     Standards Track
        Date:       December 2002
        Mailbox:    hari@lcs.mit.edu, padmanab@microsoft.com,
                    gorry@erg.abdn.ac.uk, mahesh@erg.abdn.ac.uk
        Pages:      41
        Characters: 108839
        See Also:   BCP 69
                                      
        I-D Tag:    draft-ietf-pilc-asym-08.txt

        URL:        ftp://ftp.rfc-editor.org/in-notes/rfc3449.txt

This document describes TCP performance problems that arise because of
asymmetric effects.  These problems arise in several access networks,
including bandwidth-asymmetric networks and packet radio subnetworks,
for different underlying reasons.  However, the end result on TCP
performance is the same in both cases: performance often degrades
significantly because of imperfection and variability in the ACK
feedback from the receiver to the sender.

The document details several mitigations to these effects, which have
either been proposed or evaluated in the literature, or are currently
deployed in networks.  These solutions use a combination of local
link-layer techniques, subnetwork, and end-to-end mechanisms,
consisting of: (i) techniques to manage the channel used for the
upstream bottleneck link carrying the ACKs, typically using header
compression or reducing the frequency of TCP ACKs, (ii) techniques to
handle this reduced ACK frequency to retain the TCP sender's
acknowledgment-triggered self-clocking and (iii) techniques to
schedule the data and ACK packets in the reverse direction to improve
performance in the presence of two-way traffic.  Each technique is
described, together with known issues, and recommendations for use.  A
summary of the recommendations is provided at the end of the document.

This document is a product of the Performance Implications of Link
Characteristics Working Group of the IETF.

This document specifies an Internet Best Current Practices for the
Internet Community, and requests discussion and suggestions for
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