22 Sep
1998
22 Sep
'98
2:06 p.m.
As long as we are being specific about this, I omitted data compression too
V42bis compression is probably not very useful if the data is already compressed either at the application level [gif, tiff, mpeg] or at PPP. By the way, V42 [LAP-M] does not just add frame overhead. It is a full blow error correction and flow control protocol and as such can add sizable retransmission delay if the link is noisy and SREJ [selective reject ... similar in concept to TCP SACK] is not used. Note that it is a bit of an irony that even though an application decide to use UDP because it specifically do not need or even want flow control and error correction, componenet in the path such as the modem will go ahead and do it anyway :-( Regards, John