Subject: [L2tpext] FR over PWs

From: Javi <[email-masked]>
Date: Sun, 20 Nov 2011 14:32:31 +0100

In the emulation of Core-LAPF links over PWs:

a) [RFC4591] (FRoPW L2TPv3):

     + FRPW Payload: Core-LAPF PDU is transported in its entirety, 
excluding flags and FCS, bit stuffing is undone. So, FRPW payload 
transports Core-LAPF "address and data" fields.

     + L2-Specific Sublayer: presents if sequencing or other features 
required. The Default format defined in Section 4.6 of [RFC3931] MUST be 
used.

     + Bits of the Core-LAPF Address:
        * C/R: conveyed transparently.  Its value MUST NOT be changed by 
the LCCE.
        * FECN, BECN, DE: MAY be set by the LCCE.

b) [RFC4619] (FRoMPLS):

     + FRPW Payload: Core-LAPF PDU is transported in its entirety, 
excluding bit/byte stuffing, frame relay header, and FCS. I understand 
"frame relay header" means "Core-LAPF address field". So, FRPW payload 
would ONLY transport Core-LAPF data field.

     + L2-Specific Sublayer (CW): always presents, with the bits C, D, F, B

     + Bits of the Core-LAPF Address:
        * C/R: copied unchanged in the CW (bit C)
        * FECN: copied in the CW (bit F). If it is not already set, it 
MAY be set as a result of ingress frame policing.
        * BECN: copied in the CW (bit B). If it is not already set, it 
MAY be set as a result of ingress frame policing.
        * DE: copied in the CW (bit D). If it is not already set, it MAY 
be set as a result of ingress frame policing.

Why these differences?.

In RFC4591, I understand FRPW payload transports "Core-LAPF address 
field", but egress LCCE does not use it (apart from "C/R" bit). Why?

Why does RFC4591 transports "Core-LAPF address field" in the FRPW 
payload insteed of using the L2-Specific Sublayer such as RFC4619?