Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.3 4.3bsd-beta 6/6/85; site ucbvax.BERKELEY.EDU Path: utzoo!watmath!clyde!cbosgd!ucbvax!telecom From: telecom@ucbvax.UUCP Newsgroups: mod.telecom Subject: Re: FASTLINK (tm) "10,000 bps or faster" modem Message-ID: Date: Thu, 21-Nov-85 13:43:17 EST Article-I.D.: SIMTEL20.KPETERSEN.12161705692.BABYL Posted: Thu Nov 21 13:43:17 1985 Date-Received: Wed, 18-Dec-85 03:02:31 EST Sender: serge@ucbvax.BERKELEY.EDU Organization: The ARPA Internet Lines: 22 Approved: telecom@mit-xx.arpa Unfortunately, the fact that the modems have error correction built in does not mean you don't need end to end error correction. Loss of data, particularly on busy Unix systems, is very common at even moderate speeds on serial input lines. So the fact that the data got between the modems intact does NOT mean that the data got from the modem to the computer, or from the computer to the modem without loss (particularly if the modems are busy doing retries and are unable to accept new data at full speed). Early indications are that these sorts of flow problems are so common that per packet error checking is still the most efficient way to go, with the issue of packet size being a yet to be determined variable. Overall flow control issues are also still not fully worked out. Right now, we're planning to work with standard file transfer programs and test different flow control techniques and block sizes to see how the modems perform in real life. However, we've all agreed that per block error checking should be maintained over dialup lines, just as it is at lower speeds. These modems may have some uses, but they are definitely not the ultimate. Their lack of true full duplex capability is a very significant factor. --Lauren--