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what are the major differences between HDLC and PPP? How are they
mainly used?

answers wrote:
> what are the major differences between HDLC and PPP? How are they
> mainly used?

And forgot to mention...what are the differences between PPP and Frame
relay ?

answers wrote:
> answers wrote:
> > what are the major differences between HDLC and PPP? How are they
> > mainly used?
>
> And forgot to mention...what are the differences between PPP and Frame
> relay ?


Perhaps you could post the results of your own research so far and then
we can comment

PPP and Frame Relay both are l2 protocols.
I know about PPP, about CHAP etc. I know a few things about FR
also..Like the packets are broken down into frames and transmitted, and
about DLCIs.. But I am not able to get the exact differences between
PPP and Frame Relay..

HDLC is used on point-to-pont serial links suc as T1s, DS3 and now
Packet-over-SONET (POS). It has a low overhead in terms of the
additional bytes required over and above the layer 3 payload. There is
no authentication protocol for HDLC.


PPP was and is heavily used in async dial-up and provide for
authentication using PAP or CHAP protocol. Now there is also PPP over
Ethernet (PPPoE).

A variation of PPP known as multi-link PPP (MLPPP) is quite popular for
loading balancing parallet circuit like T1's.

> HDLC is used on point-to-pont serial links suc as T1s, DS3 and now
> Packet-over-SONET (POS). It has a low overhead in terms of the
> additional bytes required over and above the layer 3 payload. There is
> no authentication protocol for HDLC.
>
> PPP was and is heavily used in async dial-up and provide for
> authentication using PAP or CHAP protocol. Now there is also PPP over
> Ethernet (PPPoE).

PPP and Cisco HDLC has the *same* amount of overhead. PPP is the more
modern and probably better maintained protocol. PPP is also heavily used
on point-to-pont links.

Steinar Haug, Nethelp consulting,

I thought PPP has a 2 byte protocol field in addition to the flag,
control and address fields

> I thought PPP has a 2 byte protocol field in addition to the flag,
> control and address fields

Yes, so does Cisco HDLC. See

http://www.nethelp.no/net/cisco-hdlc.txt

for a description of the format.

Steinar Haug, Nethelp consulting,

If you ever want to run VoIP over your data networks always run PPP or
Frame Relay. HDLC does not handle fragmentation well, jitter can be
controlled and is more predictable with PPP and Frame Relay .

James

Steinar Haug wrote:
> > I thought PPP has a 2 byte protocol field in addition to the flag,
> > control and address fields
>
> Yes, so does Cisco HDLC. See
>
> http://www.nethelp.no/net/cisco-hdlc.txt
>
> for a description of the format.
>
> Steinar Haug, Nethelp consulting,

> If you ever want to run VoIP over your data networks always run PPP or
> Frame Relay. HDLC does not handle fragmentation well, jitter can be
> controlled and is more predictable with PPP and Frame Relay .

Um, Cisco HDLC does not handle fragmentation *at all* - but that's okay
as long as IP does it. If you want your link layer protocol to handle
fragmentation I agree that PPP may be a better choice.

On the other hand, for basic, non-fragmented packets PPP, Cisco HDLC and
Frame Relay all give you mostly the same functionality (with the addition
of an extra multiplexing field, the DLCI, for Frame Relay).

Steinar Haug, Nethelp consulting,