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IMPROVING THE PERFORMANCE OF TCP IN WIRELESS NETWORKS THROUGH INTER-LAYER COMMUNICATION

IP.com Disclosure Number: IPCOM000008650D
Original Publication Date: 1998-Mar-01
Included in the Prior Art Database: 2002-Jul-01
Document File: 2 page(s) / 127K

Publishing Venue

Motorola

Related People

Mouayad J. Albaghdadi: AUTHOR

Abstract

The Transport Control Protocol (TCP) was designed and fine tuned for wireline networks and stationary hosts. When operating in a wireless envi- ronment, the collection of algorithms that make up TCP misinterpret the behavior of the underlying network leading to less than optimal operation of TCP.

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Technical Developments

IMPROVING THE PERFORMANCE OF TCP IN WIRELESS NETWORKS THROUGH INTER-LAYER COMMUNICATION

by Mouayad J. Albaghdadi

ABSTRACT

  The Transport Control Protocol (TCP) was designed and fine tuned for wireline networks and stationary hosts. When operating in a wireless envi- ronment, the collection of algorithms that make up TCP misinterpret the behavior of the underlying network leading to less than optimal operation of TCP.

  In this paper we will propose an approach to this problem. Layer two (the wireless network) will provide a list of parameters to TCP defining its characteristics. This will enable TCP to fine tune its algorithms for better performance.

INTRODUCTION

  The Transport Control Protocol (TCP) is arguably the most widely used transport layer protocol due to the explosive growth in the TCPilP based Internet in recent years and will continue to be used by mobile users. Since TCP is designed for wireline networks it interprets packet loss as a sign of network congestion. Therefore, on detecting lost packets, procedures to alleviate the congestion are initiated. Since error rates are sufficiently small in wireline networks the assumption that packet loss

occurs only due to congestion is acceptable and TCP performs satisfactorily. For wireless channels, the error rates are significantly higher and the prob- ability of packet loss due to errors is significant (compared to wireline channels). Therefore, in wireless environments TCP interprets loss of packets due to errors as also resulting from network congestion and initiates congestion alleviation procedures; even when there is no congestion in the network. Frequent errors imply that optimal window size is never achieved, leading to signifi- cant degradation in performance.

  A previously proposed approach' employs the use of last hop acknowledgments (LHACKs). In this scheme, the Base Station transmits an acknowledgment (LHACK) for every packet it forwards to the wireless network that arrived from the wireline network. Similarly, a first hop ACK (FHACK) is transmitted for packets going from wireless to the wireline network. The LHACK is transmitted independently of the acknowledgment that is transmitted by the destination as per TCP requirements. Packets for which LHACKs are received, but no ACKs, are determined to be lost due to errors on the wireless hop. Therefore window sire is not adjusted following the loss of packets for which LHACKs was received. The usefulness of LHACKs is limited by (i) the increased traffic due to multiple acknowledgments for each packet and
(ii) the processing burden placed on the Base Station and the transmitting station.

  In general, the above approach breaks the TCP end-to-end connection into two separate connec- tions, a wireline and a wireless connections.

OUR SOLUTION

  During connection establishment, layer 2 (the wireless part of the network) needs to pass list of parameters to both ends of the connection which def...