PPP

alimoe

I don't understand how HDLC is encapsulated with PPP. Granted HDLC is a point-to-point protocol but what I don't understand is if you have 2 routers where one is Cisco and another is non-Cisco PPP can be used as an encapsualtion and HDLC you cannot be used. But like I mentioned HDLC is encapsulated in the PPP frame. Can someone answer this question. Thanks.

bonam004

HDLC - used between Cisco Routers
PPP - Cisco and non-Cisco Routers

HDLC is proprietary - It took place of the SDLC

alimoe

I understand that, but PPP is encapsulated with HDLC so how is it possible for a Cisco router and a non-Cisco router to communicate??

djjit

Note: HDLC is an industry standard bit-oriented data link layer protocol. It specifies an encapsulation method for data on Synchronous serial data links using frame characters & check sum. And it is point-to-point used on leased lines. Now, what Cisco has done is they have modified the HDLC frame format by adding a proprietary Data field. This is what all vendors do. So that, each vendor has a different way of communicating with the Network layer protocols.

The PPP protocols stack comprises of 4 main components(As per Todd Lammle).
1. EIA/TIA-232-C
2. HDLC
3. LCP
4. NCP
The HDLC component here is the industry standard for encapsulating datagrams over serial links. I hope this would help. NB. According to Cisco EIA/TIA-232-C and HDLC are combined in to one and called A method for encapsulating multi-protocol datagrams

http://www.cisco.com/en/US/tech/tk713/tk507/tech_protocol_family_home.html

alimoe

I have another question. Is HDLC also part of the ppp protocol stack when it used over asynchrnous lines? I'm assuming no because HDLC is only for synchrnous connection....