Subject: Some questions on Interworking in MPLS/ GMPLS

From: "Mohammad Siddiqui" <[email-masked]>
Date: Wed, 06 Mar 2002 19:44:22 +0000

Hi:

I have some basic question on interworking between classical MPLS and G-MPLS 
based network. I assumed that we can have a network where we can have both 
MPLS and G-MPLS based nodes.

To see the interworking issue that I am questioning about, consider the 
following change in label request object from MPLS to G-MPLS,

Label request in Classical MPLS:
================================
0                   1                   2                   3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|            Length             | Class-Num (19)|C-Type (1)     |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|              Reserved	        |             L3PID             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Generalized Label request in G-MPLS:
=====================================

0                   1                   2                   3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|            Length             | Class-Num (19)|C-Type (4)[TBA]|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LSP Enc. Type |Switching Type |             G-PID             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Notice the diference in the c-type. Now to further illustrate on the 
question that I've, please consider the following topology, where nodes 
markes as G-x are G-MPLS based nodes and the nodes marked as M-x are 
classical MPLS based nodes.

G-1 ----- G-2 ----- M-2

Now consider the case where GMPLS node G-1 wants to establish a connection 
with MPLS node M-2. GMPLS node G-1 sends a PATH message with G-label request 
object with c-type = 4. Now GMPLS node G-2 wants to forward the PATH message 
to MPLS node M-2; the following are two possibilities.

1. If G-2 just sends label request in the G-MPLS way, i.e., with c-type = 4, 
the M-2 may/ will just reject the message as it expects a c-type of 1. So, 
this may/ will not work. Comments?

2. G-2 some how knows that M-2 is MPLS based node (how? I don't know, 
comments?) and prepares a PATH message with "old" label request object with 
c-type = 1.

The above is an example case where there are some questions in my mind  
w.r.t. to interworking in a hybrid MPLS and G-MPLS network. We can also 
think of the similar questions on the other objects where c-type or some 
other parameters has been changed from MPLS to G-MPLS.

I thought that the changes in OSPF and ISIS are quite consistent with the 
upgrade to G-MPLS from MPLS but will be very much interested in hearing some 
issues that anyone is aware of, w.r.t. routing in a hybrid MPLS/ G-MPLS 
based network.

Many thanks in advance for sharing the knowledge and helping me in this 
regard.

Thanks

-- Siddiqui

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