Subject: Re: Label Stack

From: [email-masked]
Date: Tue, 12 Jun 2001 11:17:54 +0530

sorry my mail client messed up the figure. I willl try and make it clearer below

[email-masked] on 06/12/2001 11:04:18 AM

To:   [email-masked]
cc:    (bcc: Sumit Chauhan/HSS)

Subject:  Label Stack

hi all!
     I have a very basic question. Consider the LSP setup below

R1-------------R2-----------------R3-------------------R4---------------------R5------------------R6

Eth Links = R1-R2, R2-R3, R5-R6
ATM Links = R3-R4, R4-R5
LSP1 = R1 to R6
LSP2 = R3 to R5
LSP Tunnel = R3-R4-R5 (i.e. LSP2)

Now packet reaches R3 and R3 knows that the packet has to be sent out on an ATM
outgoing interface with an ATM label space which is a tunnel. According to my
understanding firstly the packet received(Ethernet payload with shim header)
would be segmented into ATM cells and then tagged with the outgoing ATM VCI/VPI
. Now seemingly this is a label stack but if we go by a more strict definition
it is not as the stack is not part of each cell that is being carried. This is
beacause the packet (IP + shim) was segmented and carried as ATM cells and hence
only a small fraction (if not just one!) shall carry the shim header. Do we
still say that this is a label stack?

regards
sumit