> James Courtier-Dutton <dutton@livingston-ent.co.uk> wrote:
> > ISDN PPP gives better performance than V.120, this is because V.120 adds a
> > lot of overhead because V.120 is Async, and ISDN is sync.
>
> Does anyone have a good URL or ISBN for a reference to learn about what
> all this actually means?
There are two general comms books I'd recommend:
1) "Computer Networks" by Andrew S Tanenbaum, ISBN 0-13-394248-1
2) "Computers in Communications" by Gorden Brebner, ISBN 0-07-709198-1
> What is the difference between "sync" and "async" in this context?
When sending data between two entities you need to be able to maintain the
structure of the data (e.g. bytes, packets, frames, etc). There are two
ways of doing this:
1) Asynchronous transmissions are sent without precise clocking. Such
signals generally have different frequencies and phase relationships.
Asynchronous transmissions usually encapsulate individual characters in
control bits (called start and stop bits) that designate the beginning and
end of each character.
2) Synchronous transmissions are sent with precise clocking. Such signals
have the same frequency, with individual characters encapsulated in
control bits (called start bits and stop bits) that designate the
beginning and end of each character.
In an ISDN context, asynchronous means that the timing signals are sent in
the B-channel along with the rest of the data and synchronous means that
the timing signals are sent in the D-channel (which means you get your
full 64kbps for data).
> Why would you use PPP over ISDN and how does it work?
Because this usually means "PPP over ISDN, synchronous" as opposed to
V.120 which is asynchronous.
> What's V110,
V.110 is a bit rate adaptation protocol defined by International
Telecommunication Union (ITU). V.110 provides a standard method of
encapsulating data over GSM and ISDN networks.
> V120
V.120 is an asynchronous protocol for encapsulating data over ISDN.
> and X75?
Not too sure. AFAIK, it's an "inter-networking" protocol that's use to
join X.25 networks together. I'm a bit fuzzy on what it has to do with
ISDN.
> What do the different values for 'Line Speed' mean in the PM3? (e.g.
> '64000', '64000/async')
64000 is synchronous 64k and 64000/async is asynchronous 64k (i.e. V.120).
-- Richard Morrell richard@ednet.co.uk System Administrator - edNET: Internet Access for Edinburgh - www.ednet.co.uk
- To unsubscribe, email 'majordomo@livingston.com' with 'unsubscribe portmaster-users' in the body of the message. Searchable list archive: <URL:http://www.livingston.com/Tech/archive/>