Subject: [Simple] About discover MSRP relay

From: Noriaki TAKAMIYA <[email-masked]>
Date: Wed, 30 Aug 2006 18:29:57 +0900 (JST)

Hi,

  I'm newbie about this WG, but I have a question.

  When MSRP client wants to know the MSRP relay as the first hop, how
  does it work?

  In the draft-ietf-simple-msrp-relays-08.txt, it is described in the
  section 5.1 as the following:
----
   Clients can be configured (typically through discovery or manual
   provisioning) with a list of relays they need to use.  They MUST be
----

  And then, the following method is described in section 8:
----
   When resolving an MSRP URL which contains an explicit port number, an
   MSRP node follows the rules in section 6 of the MSRP base
   specification.  MSRP URLs exchanged in SDP and in To-Path and From-
   Path headers in non-AUTH requests MUST have an explicit port number.
   (The only message in this specification that can have an MSRP URL
   without an explicit port number is in the To-Path header in an AUTH
   request.)

   The following rules allow MSRP clients to discover MSRP relays more
   easily in AUTH requests.  If the hostport of an msrps: URL is an IPv4
   address or an IPv6 reference and no port number is provided, use the
   default port number assigned by IANA.  If the hostport is a domain
   name and an explicit port number is provided, attempt to look up a
   valid address record (A or AAAA) for the domain name.  Connect using
   TLS over the default transport (TCP) with the default port number.

   If a domain name is provided but no port number, perform a DNS SRV
   [4] lookup for the '_msrps' service and '_tcp' transport at the
   domain name, and follow the SRV selection algorithm defined in that
   specification to select the entry.  (An '_msrp' service is not
   defined, since AUTH are only sent over TLS.)  If no SRV records are
   found, try an address lookup (A or AAAA) using the default port
   number procedures described in the previous paragraph.  Note that
   AUTH requests MUST only be sent over a TLS-protected channel.  An SRV
   lookup in the example.com domain might return:
   :
----

  Some books describe that SIP INVITE is sent after AUTH requests are
  completed. In this situation, MSRP client can't know the first MSRP
  relay....

  So, I have a qeustion:

  o Is the above discovery applied to find the first MSRP relay?
  o If yes, what does domain mean in this case? Is it the domain of
    MSRP client issuing the MSRP message, that of the peer MSRP client
    or configured MSRP relay's domain?

  If I misses some points, could you point any references?

  Regards,

--
Noriaki Takamiya

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---

From: Ben Campbell <[email-masked]>
Date: Wed, 30 Aug 2006 08:17:49 -0500

HI,

The text you quote merely talks about how your figure the IP address  
and port to use based on a known MSRP URL. We have not defined a  
mechanism to discover that. Currently an MSRP client will need to be  
configured to know if it should use a relay, and if so, the URL for  
that relay.

It is possible we could define a more automatic discovery mechanism  
in the future, but we do not have one at present.

Hope this helps!

Ben.

---

From: Noriaki TAKAMIYA <[email-masked]>
Date: Thu, 31 Aug 2006 13:58:28 +0900 (JST)

Hi, Ben,

>> Wed, 30 Aug 2006 08:17:49 -0500
>> [Subject: Re: [Simple] About discover MSRP relay]
>> Ben Campbell <[email-masked]> wrote...

> configured to know if it should use a relay, and if so, the URL for  

  I see. Thanks.

--
Noriaki Takamiya