Cell Relay Archive

[Geert Goossens <gagoosse@info.vub.ac.be>]

Jim Jackson wrote:
> 
> On Tue, 22 Jul 1997, Geert Goossens wrote:
> 
> > As for other protocols: I don't think I can be of much help. There is of
> > course a 'native' reliable ATM adaptation layer, AAL3/4, but it does not
> > seem to be very popular (I do not know of the reason).
> 
> Sorry but this is spurious. AAL3/4 (or any other AAL) is NOT the same as
> TCP in any way whatsoever. The various AALs are ways of coding and
> carrying large data units in cells. The only aspect of 'reliability' they
> cover are the ability to detect some transmission errors, e.g. cell loss.
> 
I must admit I have only had a very vague look of AAL3/4. I must have
misunderstood its capabilities. Thank you for putting this right.

> Aspects such as how to provide acknowledgements/retransmissions/timeout
> handling etc etc, are all extra and over and above the AAL stuff. How all
> these aspects of reliable data transfer are handled, dictates the
> throughput data rates you will get in real networks.
> 
Would it be conceptually so wrong to make a reliable AAL? (Of course,
you can always put a higher protocol in an AAL5 payload, so it isn't
really necessary.)

> AFAIK TCP has had more work on it than anyother protocol in this area -
> there are mountains of simulations, realtime analysis, etc in the
> literature. Modern workstations/PCs suitably configured can get
> 100Mbits/sec of TCP throughput over 155 OC3 ATM links in the local
> area.
> 
That does not mean TCP performs well in all circumstances, though. But,
you're right, it is a well understood protocol and readily available on
many (not to say on all) platforms. I can't give any worthy alternatives
either, ;-).

> Jim Jackson

Geert.
-- 
 Geert Goossens   (gagoosse@info.vub.ac.be)  
 Digital Telecom Department INFO/TW          
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