alimoealimoe Member Posts: 17 ■□□□□□□□□□
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.


  • bonam004bonam004 Member Posts: 38 ■■□□□□□□□□
    HDLC - used between Cisco Routers
    PPP - Cisco and non-Cisco Routers

    HDLC is proprietary - It took place of the SDLC icon_lol.gif
  • alimoealimoe Member Posts: 17 ■□□□□□□□□□
    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??
  • djjitdjjit Member Posts: 40 ■■□□□□□□□□
    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

  • alimoealimoe Member Posts: 17 ■□□□□□□□□□
    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....
Sign In or Register to comment.