slip

[Raymond Nijssen]

larry at nstar.uucp (Larry Snyder) writes:
>We have SLIP up and running here on nstar - and throughput
>over Telebits is very bad - while 2400 baud appears faster - 
>it is as expected still quite - so I guess V.32 is the next path.

The Telebit Trailblazer PEP mode is in fact a half duplex mode, so it
will behave like a modem in HST mode: SLIP really _needs_ real full duplex
connections. The performance penalty when using half duplex lines due to
enormous extra overhead (for line turnarounds, trashing/rebuild of the 
compression tables etc.) could be up to 500%

>Are the new V.32 with v.42bis modems the way to go with SLIP?
Definitely yes. These modems support full duplex transmissions with
data compression.

>Will it be possible to get throughput in the 15 kbytes range
>with these new modems (in excess of the carrier rate - after all
>the modem manufactures claim throughput in excess of 20,000 bps?)
I don't know what you mean with 'carrier rate', but I guess you mean the
'(raw) bits per second' rate. (which should not be confused with the
'baudrate'). Well, whenever a manufacturer claims their modems have a
througput in excess of 20kbps, they only give you a guarantee that their
device will never exceed this rate. In real life, the probability distribution
over the transmission alphabet is such, that in spite of advanced data 
compression algorithms used in the modems, the throughput improvement because 
of data compression is av. 50%. Obviously, this figure will be much lower
when files are transmitted which are already compressed.

______________________________________________________________________________
Raymond X.T. Nijssen  /                     / Oh VMS, please forgive me all
raymond at ele.tue.nl   /                     / unfriendly things I said about you