Subject: Session Negotiation.

From: T M Kishore <[email-masked]>
Date: Wed, 17 Nov 1999 17:47:11 +0530

Hi  All,
            My understanding is that one LSR Can support both Downstream On 
Demand and Unsolicited  at  a time.
             If  the LSR supports both Downstream On Demand and 
Unsolicited, How the LSR will inform to its neighbour that it is supporting 
both.
         In draft draft-ietf-mpls-ldp-06.txt   ,  Page No : 54 , it says as 
follows.

         If one LSR proposes Downstream Unsolicited and the other
         proposes Downstream on Demand, the rules for resolving this
         difference is:

           - If the session is for a label-controlled ATM link or a
             label-controlled Frame Relay link, then Downstream on
             Demand must be used.

          A -----> B
        If  LSR  A is supporting Downstream On Demand and LSR B is 
supporting Unsolicited over an ATM Link, If LSR B sends initialization 
Message ( with Unsolicited Mode) to LSR A , session between A and B should 
use Downstream on Demand . So LSR B has to switch over to Downstream On   
Demand Mode for this session.
          If one LSR supports Unsolicited, Is that mean that it has to 
support Downstream On Demand also ?
      Please Clarify my doubt.
Thanks in advance,
Kishore .

T M Kishore,
Senior Software Engineer,
HDF, Future Software Pvt Ltd,
480 - 481, Anna Salai, Nandanam,
Chennai - 600 035
India.
Phone : +91-44-4330550 Ext.412

---

From: Bob Thomas <[email-masked]>
Date: Wed, 17 Nov 1999 08:14:39 -0500

Kishore,

> Unsolicited, How the LSR will inform to its neighbour that it is supporting 

I don't think it is necessary for an LSR to inform a given peer that
it supports both.  It only needs to state in the Initialization message
its preference for the peer session.

> Demand Mode for this session.

Correct.

> support Downstream On Demand also ?

If it supports label distribution for label-controlled ATM and/or FR
links, and if it needs to interoperate with other LSRs that prefer
DoD for such links (in my opinion, other LSRs are likely to prefer DoD
for such links), then it will need to support DoD.

Bob