Subject: [PWE3] HDLCPW L2TPv3 (RFC 4349): Transport of LAPD frames

From: Javi <[email-masked]>
Date: Tue, 21 Jul 2009 10:55:35 +0200

Chapter 4.1: Data Packet Encapsulation

    Since all packets are passed in a largely transparent manner over the
    HDLCPW, any protocol that has HDLC-like framing may utilize the
    HDLCPW mode, including PPP, Frame-Relay ("port to port" Frame-Relay
    transport), X.25 (LAPB), etc.

I have read many times: "LAPD (derived from LAPB) is a subset of the 
HDLC structure, although it has extensions beyond HDLC"

Which are these extensions?. In any case, may does HDLCPW mode be used 
to transport LAPD frames?. Why yes or not?

Thanks

Javier Muñoz

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From: Stewart Bryant <[email-masked]>
Date: Tue, 21 Jul 2009 14:15:41 +0100

I am not sure how much LAPD there is still in existence.

LAPD would look like any other HDLC packet to an HDLC PW.

Stewart

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From: Javi <[email-masked]>
Date: Tue, 21 Jul 2009 18:38:30 +0200

> I am not sure how much LAPD there is still in existence.
There are many reasons to support LAPD. For example, the accommodation 
of legacy PSTN/ISDN terminals and/or interworking with the PSTN/ISDN
is an important consideration with respect to NGN deployment (ITU-T Y.2012)
> LAPD would look like any other HDLC packet to an HDLC PW.
However, LAPD is not mentioned in RFC 4349 neither other document about 
HDLCPW.
Does HDLCPW support these extensions of LAPD beyond HDLC?

Javier Muñoz
>> Which are these extensions?. In any case, may does HDLCPW mode be 
>> used to transport LAPD frames?. Why yes or not?
>>
>>
>> Thanks
>>
>> Javier Muñoz
>>
>>

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From: Carlos Pignataro <[email-masked]>
Date: Wed, 22 Jul 2009 10:44:08 -0400

[moving to <[email-masked]> since the reference of RFC4349]

Javier,

As Stewart answered, LAPD would look like any other HDLC packet to an
HDLC PW. All the data (address (SAPI/TEI), control, etc) is opaque to
the HDLC PW; flags and trailing FCS are stripped, and there rest is
transported.

Thanks,

-- Carlos.