[e2e] Saratoga was RE: HARQ

[L.Wood@surrey.ac.uk]

HARQ is just a name for combining ARQ with FEC. Since ARQ (without FEC - see RFC3366) can be done over FEC in a separate higher layer anyway, this is arguably implementation detail to try and increase efficiency by closely combining the two, with incremental redundancy varying repeats to increase likelihood of correct reception from combining coded frames.

Yes, Saratoga uses NACKs. It's designed for high utilisation of otherwise unused links in private networks. Two Saratoga peers can multiplex multiple flows between them. Allocation of link capacity between multiple nodes can be done by a MAC layer, or by a coarse scheduling algorithm; this depends on the scenario, and is not specified. Congestion control is optional and not specified; when you own the link, the traffic and the nodes, you can rely on knowledge of your environment and scheduling without congestion control presuming that every errored packet is a loss - again, to try and increase efficiency. Or you could reimplement TCP-Friendly Rate Control (TFRC) to make Saratoga behave like TCP - but DCCP, SCTP and TCP already do that; Saratoga is intended to be useful in environments where those protocols become performance-limited by the prevailing terrestrial-shared-Internet assumptions that make them so useful elsewhere. Saratoga's strengths are TFRC's weaknesses, and vice versa.

L.

Saratoga: http://www.ee.surrey.ac.uk/Personal/L.Wood/dtn/

<http://www.ee.surrey.ac.uk/Personal/L.Wood/><L.Wood at surrey.ac.uk>



-----Original Message-----
From: Detlef Bosau [mailto:detlef.bosau at web.de]
Sent: Mon 2007-08-27 16:31
To: Wood L Dr (Electronic Eng)
Cc: end2end-interest at postel.org
Subject: Re: [e2e] HARQ
 
L.Wood at surrey.ac.uk wrote:
>
> See http://en.wikipedia.org/wiki/Hybrid_ARQ
>
;-)

I looked at this page before.

However, the difference between "old" ARQ and HARQ I becomes not quite 
clear to me.

> .
>
> Saratoga: http://www.ee.surrey.ac.uk/Personal/L.Wood/dtn/
>


So, you flood the receiver with a well defined set of blocks and the 
receiver reports any blocks which are missing?
At least, this appears to be the basic idea. Is this correct?

Will this work when there blocks of several flows mixed, as it happens 
on an air interface in mobile networks?

Detlef

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