Browse Prior Art Database

METHOD FOR TRANSMITTING TRANSPORT LAYER ACKNOWLEDGMENTS IN A PACKET DATA SYSTEM

IP.com Disclosure Number: IPCOM000008203D
Original Publication Date: 1997-Jun-01
Included in the Prior Art Database: 2002-May-27
Document File: 3 page(s) / 135K

Publishing Venue

Motorola

Related People

Guy Romano: AUTHOR [+3]

Abstract

There is a high degree of acknowledgment overhead when running a reliable transport layer protocol over a reliable link layer protocol. A reliable protocol guarantees to deliver a number of data packets from one machine to another without duplication, loss, or reordering. Packets delivered with an unreliable protocol may be lost, duplicated, or reordered. The acknowledgment overhead includes li.nk layer acknowledgments, transport layer acknowledgments, and link layer acknowledg- ments of transport layer acknowledgments. The latter type of acknowledgments occur because transport layer acknowledgments are treated as regular packet data traffic at the link layer and are therefore acknowledged by the link layer. Figure 1 shows an example of a reliable transport layer protocol (TCP) sending data over a reliable link layer protocol.

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64 MOTOROLA Technical Developments

METHOD FOR TRANSMllTlNG TRANSPORT LAYER ACKNOWLEDGMENTS IN A PACKET DATA SYSTEM

by Guy Romano, Ken Crisler and Bryan Thale

THE PROBLEM TO BE SOLVED

  There is a high degree of acknowledgment overhead when running a reliable transport layer protocol over a reliable link layer protocol. A reliable protocol guarantees to deliver a number of data packets from one machine to another without duplication, loss, or reordering. Packets delivered with an unreliable protocol may be lost, duplicated, or reordered. The acknowledgment overhead

includes li.nk layer acknowledgments, transport layer acknowledgments, and link layer acknowledg- ments of transport layer acknowledgments. The latter type of acknowledgments occur because transport layer acknowledgments are treated as regular packet data traffic at the link layer and are therefore acknowledged by the link layer. Figure 1 shows an example of a reliable transport layer protocol (TCP) sending data over a reliable link layer protocol.

Transport Layer

Transport Layer

TCP Data

Link Layer

Packet (1)

TCP Data

b

4 Packet ACK (1)

TCP ACK

Packet (2) 4

4

TCP ACK

Packet ACK (2)

b

Mobile Host

Subscriber Unit

Base Fixed

Host

Fig. 1 TCP/IP Traffic via Reliable Link Layer Service

  The acknowledgment overhead reduces channel capacity. This increases congestion and reduces the number of users a given system can support.

  Excessive acknowledgments are a greater prob- lem in wireless packet data systems because chan- nel contention accesses are associated with link layer packets transmitted in the inbound direction. A channel contention access is a request by a unit to

reserve a fixed amount of channel bandwidth for the transmission of one or more link layer packets. Each transport layer data packet and transport layer acknowledgment sent inbound may have a channel contention access associated with it. Reducing the number of inbound link layer acknowledgments transmitted will also reduce the number of associated channel accesses.

Ohfawro~ Inc. ,997 I27 June 1997

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0 M

MO7VROLA Technical Developments

THE INVENTION

  This invention allows a link layer protocol manager to discriminate between the packets arriving at the lii layer. Packets would be grouped into one of two categories, transport layer acknowl- edgments and all other traffic. Transport layer acknowledgments would be transmitted using an unreliable link layer service while the remainder of traffic would use the reliable link layer service. Figure 2 shows an example of the invention using TCP as the transport layer.

  Data packets are transmitted using the reliable link layer because a partially received or lost dat...