The MPLS WG Archive

["Santosh Gupta" <santoshg@daewoo.dti.daewoo.co.kr>]

Hi Ajit

    The label stacking scenario that you mentioned is possible in MPLS, but if  we implement it on ATM then how can it be done as the  ATM cell has a fixed header size (5 bytes) and there is just 12+16 bits allocated for label (VPI/VCI ). Any suggestions.

santosh

----- Original Message -----

From: ajithn@sg.ibm.com

To: Santosh Gupta

Cc: sumitg@rocketmail.com ; Ashish Monga ; mpls@UU.NET

Sent: Tuesday, March 28, 2000 1:03 PM

Subject: Re: CR-LDP

LSP-IDs become part of the "traffic engineering state" of the network.  So
it is legitimate to define a CR-LSP, whose ingress is LER2,  stacking or
splicing with an existing CR-LSP whose ingress is LER1,  the latter being
specified by its LSP-ID.   The entity which does traffic engineering can be
thought of as "higher" than the LSR, and it knows these LSP-IDs.  At that
level, there is global (or, supra-local) knowledge.

However, from the point of view of LSRs, local knowledge is sufficient.
LSRs need to know only the LSP-IDs they participate in.

In your example,  LER2 and LSR5 do not need to know the spliced/stacked
CR-LSP's LSP-ID because all they do with it is, just pass it downward.
That remains true as we go down the request path till we hit LSR3, for
which it is intended.   So there is no need for non-participating LSRs to
be aware of the LSP-ID.

-- Ajith

--


"Santosh Gupta" <santoshg@daewoo.dti.daewoo.co.kr> on 03/28/2000 12:45:39
PM

Please respond to "Santosh Gupta" <santoshg@daewoo.dti.daewoo.co.kr>

To:   sumitg@rocketmail.com, mpls@UU.NET
cc:   "Ashish Monga" <ashish@daewoo.dti.daewoo.co.kr> (bcc: Ajith
      Narayanan/Singapore/IBM)
Subject:  Re: CR-LDP




Hi Sumit
    The concerned section of CR-LDP draft is as below.
4.7.4. ER-Hop 4: LSPID

The LSPID is used to identify the tunnel ingress point as the next
hop in the ER. This ER-Hop allows for stacking new CR-LSPs within an
already established CR-LSP. It also allows for splicing the CR-LSP
being established with an existing CR-LSP.
If an LSPID Hop is the last ER-Hop in an ER-TLV, than the LSR may
splice the CR-LSP of the incoming Label Request to the CR-LSP that
currently exists with this LSPID. This is useful, for example, at
the point at which a Label Request used for local repair arrives at
the next ER-Hop after the loosely specified CR-LSP segment. Use of
the LSPID Hop in this scenario eliminates the need for ER-Hops to
keep the entire remaining ER-TLV at each LSR that is at either
(upstream or downstream) end of a loosely specified CR-LSP segment
as part of its state information. This is due to the fact that the
upstream LSR needs only to keep the next ER-Hop and the LSPID and
the downstream LSR needs only to keep the LSPID in order for each
end to be able to recognize that the same LSP is being identified.

In this it clearly states that it is not only the Ingress LER and the LSRs
in the path of this LSP but other LERs also need to know the LSP-ID of
different LSPs. The scenario is something like

                LER1 ------> LSR2-------->LSR3------>LSR4

                LER2-------->LSR5

there is an LSP setup as shown from LER1 thru LSR2,LSR3, LSR4. Now LER5
receives a ER-TLV which says it has to make an  LSP for which the next hop
is LSR3 and the already existing LSP with the LSP-ID is to be used. Now the
question is how does LSR5 or LER2 come to know about this particular LSP-ID
which actually originated at LER1?

santosh

santoshgupta@poboxes.com


----- Original Message -----
From: Sumit Garg
To: 'ashish'
Sent: Tuesday, March 28, 2000 3:49 A
Subject: RE: CR-LDP


Hi,

LSD-ID is a TLV defined by the CR-LDP draft. It is a combination of the
LSR-ID and a 2 octect number assigned by the ingress/ initiating LSR. This
would typically be an administor assigned/ monitored quantity and thereof
known a priori for LSP splicing/ tunneling.

The LSPID is propagated to downstream LSRs in the LSP setup request.

Regards
Sumit

  -----Original Message-----
  From: ashish [mailto:ashish@daewoo.dti.daewoo.co.kr]
  Sent: Monday, March 27, 2000 03:58 AM
  To: mpls@uu.net
  Subject: CR-LDP


  In CR-LDP draft-03, one of the ER-HOP TLV types contain LSPID field that
is used for tunneling thru some existing LSP having that LSPID field.
  This means that that LSPID should be known in advance .
  How is that done.
  Does information regarding each LSP being created each having unique
LSPID is propagated to all LSR's.
  Please clarify.