Subject: data issue 3: signalling protocols

From: Matt Squire <[email-masked]>
Date: Thu, 11 Mar 1999 14:12:39 -0500

<bigger>

3) Expressing signalling protocols.  

   There seems to be consensus that we need an attribute for expressing

   the signalling protocols supported by the next-hop or gateway.  But

   there are still questions to address.  

     a) How to express a signalling protocol?   I don't believe there

        is any pre-existing standardized method for expressing

        signalling protocols, so we get to make one up. 

     b) What signalling protocols to express?  We certainly need to

        express both SIP and H323.  In the TBGP draft, H323 is

        parititioned into Q.931 and RAS.  Also, MGCP and SGCP are

        included.  

          - Is there consensus that H323 should be split into RAS and

          Q931?

          - Is there consensus MGCP and SGCP included?  

     c) Include port number?  Do we need to include the UDP/TCP on 
which

        signalling messages to the next-hop should be sent, and whether

        TCP or UDP should be used?  

     d) Include other/additional signalling parameters?

I would propose that a new registry be created for the purposes of

registering ip-telephony signalling protocols.  As usual, one registers

both a number, name, reference, contact, etc.  

On the protocols to express, I'm a little fuzzy on why MGCP and SGCP

need to have messages routed based on e164 numbers.  Not having read 
the

specs in a while, I thought that they were expressing a control 
protocol

between a call control agent and a media gateway.   I would assume that

they would know the gateways that they are managing and hence wouldn't

need to locate the gateways via routing on a phone number.  Can someone

enlighten me?

Since signalling messages can be sent/received on different ports and

using different protocols, I think that expressing whether a gateway

requires UDP or TCP, and on which port it expects to receive the

signalling protocol messages, is required.  

For (d), in draft-ietf-iptel-glp-00.txt, I included room for 
"Additional

Signalling Parameters."  The idea is to allow a place for other

signalling parameters that are required in order to establish 
signalling

connectivity to the next-hop.  Originally, I was going to place the IP

protocol and TCP/UDP port in here, but I separated them into a separate

question because they seemed required for any signalling protocol.  I

thought this field might prove useful as the list of signalling

protocols expands or as the capabilities of the protocols expand.  Note

that the purpose of this field is not to express everything about the

signalling protocol, only those parameters which are required for

connectivity.  If it can be negotiated after connecting, then it

shouldn't be here.

</bigger>

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