Rajesh Krishnan, Mark Allman, Craig Partridge, James Sterbenz. Explicit Transport Error Notification (ETEN) for Error-Prone Wireless and Satellite Networks. Technical Report No. 8333, BBN Technologies, March 2002.
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Abstract:

Wireless and satellite networks have non-negligible error rates that can significantly influence TCP performance because TCP considers every packet loss as an indicator of congestion, and thus throttles the packet transmission rate. Explicit transport error notification (ETEN) mechanisms can aid TCP in distinguishing packets that are lost due to congestion from ones that are lost due to corruption. If TCP can retransmit a packet lost due to corruption without needlessly reducing the transmission rate, a performance benefit can be realized. In this study we propose two types of ETEN mechanisms: (i) per-packet mechanisms that notify endpoints of each detected corruption; and (ii) cumulative mechanisms that notify endpoints of aggregate corruption statistics. We have implemented the proposed mechanisms in the ns-2 simulator. We present simulation results on performance gains achievable for TCP Reno and TCP SACK, using ETEN mechanisms over a wide range of bit error rates and traffic conditions. We compare TCP Reno and TCP SACK enhanced with ETEN mechanisms against TCP Westwood, which uses a bandwidth estimation strategy in place of the traditional AIMD congestion avoidance algorithm. We discuss two issues related to the practical deployment of ETEN mechanisms: corruption detection mechanisms (and their co-operation with ETEN-based recovery in the transport layer) and security aspects. We include recommendations for further work. Our conclusions from this study are:

• per-packet ETEN mechanisms offer substantial gains in bulk TCP goodput in the absence of congestion; however, in the presence of congestion TCP congestion avoidance mechanisms dominate resulting in insignificant gains from ETEN
• proposed per-packet mechanisms provide useful upper bounds on performance that can be used to evaluate future proposals of per-packet and cumulative ETEN techniques
• per-packet mechanisms present significant challenges to practical implementation by providing a new opportunity to exploit Internet security vulnerabilities and by requiring intermediate nodes to reliably extract information from the headers of corrupted packets
• cumulative ETEN techniques are more attractive to implementation; however, the particular mechanism we evaluated did not realize the potential gains of per-packet techniques
• future work in this area should focus on alternative cumulative ETEN mechanisms, accurate loss inference at endpoints to avoid tracking congestion losses at every hop, interactions with forward error correction, and cross-layer co-operation for ETEN

BibTeX:

@techreport{KAPS02,
    author      =        "Rajesh Krishnan and Mark Allman and Craig Partridge and James Sterbenz",
    title       =        "{Explicit Transport Error Notification (ETEN) for Error-Prone Wireless and Satellite Networks}",
    institution =        "BBN Technologies",
    year        =        2002,
    number      =        "TR-8333",
    month       =        mar,
}