Subject: IP packet forward from one POS link into another

From: Leo Huber <[email-masked]>
Date: Mon, 07 Jun 1999 16:07:11 PDT

hi all,

is this a correct encapsulation sequence?:

         |<-payload->|  |<------ transport ------->|

POS in:     UDP2/IP2/   PPP2/L2TP/UDP1/IP1/PPP1/SDH/-> router ->

POS out:    UDP2/IP2/   PPP3/SDH (POS) ->

1. PPP1, PPP2, IP1 and L2TP terminate in the router.
2. PPP3 originates in the router.
3. UDP2/IP2 represent a payload to forward from one POS link
into another POS link.

thx for you help

leo huber

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---

From: James Carlson <[email-masked]>
Date: 08 Jun 1999 06:47:38 -0400

> 2. PPP3 originates in the router.

I would say that PPP3 also terminates on this router; but it's just a
semantic thing.

> 3. UDP2/IP2 represent a payload to forward from one POS link

That should be "IP2'" -- any router should be modifying at least the
TTL and checksum, if nothing else.

Note that "SDH" isn't an encapsulation like any of the others in your
diagram.  All of the other encapsulations prepend a few bytes to the
PDU or do some data translation (or both).  SDH has a completely
separate framing mechanism running and looks like a byte-at-a-time
(not a packet at a time) pipe to PPP.

-- 
James Carlson, Software 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