Re: (PM) pm3 disconnects

Jon Ribbens (jon@oaktree.co.uk)
Fri, 26 Mar 1999 13:35:34 +0000

James Courtier-Dutton <dutton@livingston-ent.co.uk> wrote:
> Groups of characters are enclosed in frame marker bytes making up a frame.
> This saves on bits.
> Async sends 8 bit Bytes with at least 1 start and stop bit making a total of
> 10 bits per character.
> Sync sends groups of 8 bit bytes (say 256 bytes) enclosed in frame markers,
> (normally about 3-5 bytes)

This confuses me greatly. I thought ISDN inherently provides a method of
sending bits. Why do you need start or stop bits, which are usually sent
to synchronise clocks? The ISDN system must already have such synchronisation
at a lower layer, otherwise it could not talk on the D-channel to the switch.
Why do you need *more* synchronisation within the B channel itself?

Or is it that you *don't* need the extra synchronisation, and this is why you
should use PPP over ISDN and not V.120, in that using an asynchronous protocol
over ISDN is just pointless?

Presumably PPP is the best protocol to tell our customers to use to connect
to our PM3? If their TA does not support PPP, what is the next best protocol
to use?

Cheers

Jon

-- 
\/ Jon Ribbens / jon@oaktree.co.uk
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