Subject: PPP over FR.

From: Srinivasan Chakravarthy <[email-masked]>
Date: Thu, 02 Mar 2000 14:29:09 -0800

Hi,

I am implementing PPP over FR as per RFC 1973.  Could you pls let me know if the
address (0xFF) and control (0x03) fields should be sent with the ppp packets
(both control and data) when sent over a FR DLCI (assuming Address and Control
field compression is NOT negotiated during LCP)?

Thanks & Regards,

Srinivasan.

---

From: James Carlson <[email-masked]>
Date: 03 Mar 2000 07:04:38 -0500

> field compression is NOT negotiated during LCP)?

The address and control fields are part of the HDLC header and not
part of PPP.  Accordingly, when PPP is run over FR, the HDLC address
field is used as the DLCI, the control field is used according to the
FR specs, the PPP NLPID (hex CF) follows that, and then PPP Protocol
ID field and Information (payload) field follow.  The diagram on page
2 of RFC 1973 shows this.

You MUST NOT negotiate ACFC when running over FR.  You MUST NOT
include an extra address and control field.  Section 3.2 of RFC 1973
describes this.

(All this having been said, I've seen a number of buggy PPP
implementations.  For instance, the AO/DI folks run duplicate address
and control fields over X.25, which is rather similar to FR, in
violation of RFC 1598.  You'll likely need to do a fair bit of
interoperability testing and may need compatibility modes.  Your
mileage will vary.)

-- 
James Carlson, System Architect                     <[email-masked]>
IronBridge Networks / 55 Hayden Avenue   71.246W   Vox:  +1 781 372 8132
Lexington MA  02421-7996 / USA           42.423N   Fax:  +1 781 372 8090
"PPP Design and Debugging" --- http://people.ne.mediaone.net/carlson/ppp