Scoped Hybrid Automatic Repeat reQuest with Forward Error Correction (SHARQFEC)

last updated Feb 28 1998

Scoped Hybrid Automatic Repeat reQuest with Forward Error Correction (SHARQFEC) is a new develivery paradigm that combines the timelieness of distributed ARQ and the efficiency of FEC with traffic limiting capabilities of administrative scoping. Developed as part of the Hierarchically Partitioned Reliable Transport Protocol (HPRTP) for my Ph.D., SHARQFEC could be used in other situations where high degress of scalability are required. SHARQFEC merges three bodies of work together.

First, it incoporates the localized recovery techniques put forward within the Scalable Reliable Multicast (SRM) paper.

Second, it adds Forward Error Correction capabilities as explored by Vicisano, Nonnemacher, Rizzo, and Gemmel.

Finally, localization through the creation of tree structures is added. In this regard SHARQFEC is similar to the Log Based Receiver Relaible Multicast (LBRRM), and the Tree-based Multicast Transport Protocol (TMTP). However, SHARQFEC differs from these protocols in that explciitly uses Administrative scoping to perform lcoalization.

SHARQFEC operation can be summarized as follows:

• Receivers are members of one or more administartively scoped regions that are hierarchically arranged so that the source is in the largest scoped region and new levels are introduced the furhter away a receiver sifrom the source.
• Receivers utilize these scoped regions to restrict the flow of their traffic.
• Receivers within a region select a representative known as a Zone Closest Receiver (ZCR) that is believed to be the closest receiver within that zone to the ZCR of the next largest adminstratively scoped zone.
• Source traffic is broken up into groups of packets that are transmitted over a data channel.
• Receivers that detect missing pacekts from within the group transmit NACKs indicating the number of packets missing.
• Receivers perform suppression in a manner similar to that used by SRM, excepting that the distance used in the calculations is the distance to ZCR at the scope the NACK will be transmitted to instead of the distance to the original source.
• Receivers will restrict the scope of the repairs to the smallest possible scope, excepting ZCRs which will transmit their NACK to the next largest scope zone.
• Receivers within a zone shall periodically evaluate their distance to the ZCR of the next largest scope zone and if need be a receiver closer to the parent ZCR shall ursurp the current ZCR.
• ZCRs will maintain an estimate of the losses being experienced by the other receivers within its zone and inject FEC packets to pre-compensate for losses.

More details will be forthcoming once I manage to write them up in my thesis....

In the meantime I've included some screen dumps from my simulations using the Berekely network simulator ns and network animator nam packages. and the slides ( ps , gzipped ps ) I presented at the Orlando Reliable Multicast Research Group (Feb 22 - 24, 1998).

Roger Kermode, January 12th, 1998.