Subject: Label Stack

From: [email-masked]
Date: Tue, 12 Jun 2001 11:04:18 +0530

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

R1-------------R2-----------------R3-------------------R4---------------------R5------------------R6
            Eth                      Eth               ATM
ATM                    Eth

<------------------------------------------------>
                                                                        LSP2
<------------------------------------------------------------------------------------------------------->
                                                             LSP1

LSP1 = R1 to R6
LSP2 = R3 to R6

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