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Re: cell-retransmission in ATM--permitted or not

From: fgoldstein@bbn.com (Fred R. Goldstein)
Date: Fri, 20 Dec 1996 17:03:59 EST

In article <SAINUL-H.96Dec20183822@eagle.fedu.uec.ac.jp> sainul-h@eagle.fedu.uec.ac.jp (Hossain Sainul) writes:
>Could someone pls explain---
>1)whether cell-retransmission occurs in ATM
>2)if the answer is negative,then how the retransmission of
>cells of any TCP-packet is possible in the same architecture
>of ATM?

As other have noted, ATM doesn't attempt to deliver cells reliably.

With AAL3/4 or AAL5, a lost cell wastes the whole packet.  TCP can retransmit, 
or you can run SSCOP directly above AAL to make it "reliable", but it's also 
based on frame, not cell, retransmission.

I did once propose a selective cell retransmission AAL called BLINKBLT.  It  
uses a sequence number for each cell, bulk transmission (bitmap) of cell 
acknowledgements, and retransmission of just the lost cells.  Packet formation 
is then above, not below, cell recovery.  It should work on very lossy 
networks.  It hasn't caught on, and I don't even know where there's an online 
copy..

--
Fred R. Goldstein   k1io    fgoldstein@bbn.com
BBN Corp., Cambridge MA  USA         +1 617 873 3850
Opinions are mine alone; sharing requires permission.