Browse Prior Art Database

TCP/IP Header Compression triggering based on RF conditions

IP.com Disclosure Number: IPCOM000007617D
Original Publication Date: 2002-Apr-09
Included in the Prior Art Database: 2002-Apr-09
Document File: 5 page(s) / 165K

Publishing Venue

Motorola

Related People

Robert Sharpe, Lena Srey, Ivan Vukovic: AUTHOR

Abstract

This publication describes a method to reduce the probability of degrading TCP data application throughput for systems employing TCP/IP Header Compression with PPP in a wireless environment. TCP performance can be severely impacted when Van Jacobson Compression (RFC 1144) is employed in a wireless environment where the probability to lose TCP segments can be substantial at times. The mechanism described to avoid this condition is an enable/disable of TCP/IP header compression between PPP peers based upon a trigger that monitors RF trends that predict an increased probability to lose TCP segments such as poor RF quality.

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Title

TCP/IP Header Compression triggering based on RF conditions

Authors

Robert Sharpe

Lena Srey

Ivan Vukovic

Global Telecom Solutions Sector

Motorola, Inc.

Abstract

                    This publication describes a method to reduce the probability of degrading TCP data application throughput for systems employing TCP/IP Header Compression with PPP in a wireless environment.  TCP performance can be severely impacted when Van Jacobson Compression (RFC 1144) is employed in a wireless environment where the probability to lose TCP segments can be substantial at times.  The mechanism described to avoid this condition is an enable/disable of TCP/IP header compression between PPP peers based upon a trigger that monitors RF trends that predict an increased probability to lose TCP segments such as poor RF quality.

Body

Many connections for Internet access today use PPP(Point to Point Protocol)  as the link layer for transport of IP packets from client to Network Access Server.  For low-speed links it is very popular to use TCP/IP header compression on this link to improve link efficiency.  TCP/IP Header Compression ( also known as Van Jacobson compression) can reduce a 40 byte TCP/IP header to 3 bytes(minimum) which is a considerable bandwidth savings over a low speed link.  This bandwidth savings is greatly appreciated in a wireless data environment where RF capacity is closely scrutinized.

TCP/IP header compression can have negative effects on performance when used in an error prone networks such as a wireless environment.  Since TCP/IP header compression relies on state information from each sequential TCP segment the receiver cannot re-construct the TCP/IP header properly when a TCP segment is lost, possibly due to poor RF conditions.  All subsequent TCP segments received will fail TCP’s checksum until the original missing TCP segment is retransmitted thereby thwarting TCP Fast Retransmission if supported.  This results in significant performance degradation.   The amount of data lost due to this phenomenon is typically equal to the TCP Receive Window Size in high latency networks such as the wireless environment.  i.e. If the TCP Receive Window size is set to 32k all the data in that window will be corrupted and need to be retransmitted by TCP.

Currently, TCP/IP header compression is enabled at the Network Access Server and mobile client device during the IPCP phase of PPP setup.  Each entity inform...