lamy@sobeco.com (Jean-Francois Lamy) (09/02/90)
I'm staring at an ad in Communications Week about the Motorola UDS FastTalk V.32/42b modem that is claimed to provide throughputs of up to 38.4. We have an application currently using stat muxes over a leased digital 19.2 line that we'd like to move to TCP/IP, and compressed SL/IP (or PPP) seem like good candidates for the application. We suspect however that the additional demand created by the added functionality and extra overhead will spell the death of the 19.2 connection. Leasing 56kbps lines in Canada is outrageously expensive (8000$ a month), and we don't have enough voice traffic either to justify going to fractional T1. We've seen boxes at 7000$ each that do quite a good job muxing data from 4 channels at 38.4, compressing down to a 19.2 sync link -- we're using only one channel at 38.4. Sending pre-compressed data, however, reduces actual throughput to close to the line capacity, as one might expect (fortunately the unit does not actually degrade in those cases). But 14000$ for 2 units, plus the cost of modems and the line is a bit much. We need sustainable 19.2 at the very minimum, and more the better. Has anyone tried the Motorola UDS FastTalk V.32/V.42b and seen whether the unit will - maintain 19.2 in the presence of pre-compressed (meaning compress(1) Lempel- Ziv) data such as a bozo transferring a tape over a serial line, or will it sink down to its "native" 9600bps? - acheive anything close to 38.4 doing SLIP or PPP. (where what is flying by are either very short packets (2-10 chars) or short packets (we'd be keeping our MTU size down to keep echo latency down). I will summarize replies mailed to me. Vendor plugs welcome too, to my e-mailbox, that is. Jean-Francois Lamy lamy@sobeco.com, uunet!sobeco!lamy Groupe Sobeco, 505 ouest, bd Rene-Levesque, Montreal Canada H2Z 1Y7