HDLC Vs PPP

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.

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, snipped-for-privacy@nethelp.no

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

Yes, so does Cisco HDLC. See

Steinar Haug, Nethelp consulting, snipped-for-privacy@nethelp.no

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

Ste> > I thought PPP has a 2 byte protocol field in addition to the flag,

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, snipped-for-privacy@nethelp.no