Subject: Re: PPP and HDLC over MPLS

From: Wei Luo <[email-masked]>
Date: Wed, 26 Mar 2003 14:40:15 -0800

The base PPP protocol header does not include HDLC address and control fields. 
Only when PPP uses HDLC-like framing on certain media types, the L2 header has
these fields, but they are considered as media-specific information.

---Wei

Shahriar Rahman wrote:
> 
> Hello,
> Looking at draft-martini-ppp-hdlc-encap-mpls-00.txt (not sure if there is
> a following version of the draft), the following sections-
> 
> 4.1. HDLC
> 
>    HDLC mode provides port to port transport of HDLC encapsulated
>    traffic. The HDLC PDU is transported in its entirety, including the
>    HDLC address, control and protocol fields, but excluding HDLC flags
>    and the FCS. ....
> 
> 4.2. PPP
> 
>    PPP mode provides point to point transport of PPP encapsulated
>    traffic, as specified in [3]. The PPP PDU is transported in its
>    entirety, including the protocol field (whether compressed using PFC
>    or not), but excluding any media-specific framing information, such
>    as HDLC address and control fields or FCS.  ....
> 
> It occured to me why in one case HDLC address and control fields are
> transported and in the other they are not. It wasn't obvious to me.
> 
> _thanks for any explanation.
> regards_
> Shahriar
> 
> =================================================================
> Shahriar Rahman                             ||        ||
> Software Engineer                          ||||      ||||
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