Subject: [Simple] Discovery of an MSRP relay

From: "Miguel A. Garcia" <[email-masked]>
Date: Fri, 03 Oct 2003 08:31:59 +0300

Hi:

I would like to understand possible mechanisms to discover an MSRP relay 
in a network. Is this something that have been discussed before?

When reading the MSRP draft, section 7.1.2, I found a discussion on the 
usage of DNS SRV when the MSRP client already knows the host name of the 
  MSRP relay. Fair enough. But in most situations this requires either 
provisioning or some out of band configuration. In a roaming scenario, 
when the network changes oftenly, the address of the MSRP relay may 
change as well. So I believe there is a need for a discovery mechanism 
of the MSRP relay.

If we compare with SIP, SIP uses DNS SRV records to solve this problem. 
The input to the DNS SRV query is a network name, and the answer is a 
host name. I was wondering if is this something that we can mimic in 
MSRP, as I believe the problem are pretty similar.

Thanks a lot,

         Miguel
-- 
Miguel-Angel Garcia                     Oy LM Ericsson AB
                                         Jorvas, Finland
mailto:[email-masked]     Phone:  +358 9 299 3553
mailto:[email-masked]        Mobile: +358 40 514 0002

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From: Jonathan Rosenberg <[email-masked]>
Date: Fri, 03 Oct 2003 02:27:08 -0400

> change as well. So I believe there is a need for a discovery mechanism 

Do you mean that it changes because you'll want to use one in the 
network you just roamed into?

> MSRP, as I believe the problem are pretty similar.

The DNS SRV mechanism doesnt help you with local discovery of 
resources (i.e., the ones in the network I just roamed into). For 
that, we have been using a DHCP option code to return SIP servers. The 
analogy would therefore be to learn MSRP relays from DHCP too. 
However, I think a better model is to use DHCP to bootstrap a local 
access point (the SIP server) and from there learn everything else. 
The use of a relay might very well be something within the scope of a 
session policy that is enforced by the local network. In that case, 
the static policy mechanisms in the session policy draft:

http://www.ietf.org/internet-drafts/draft-hilt-sipping-session-policy-00.txt

would work. The registration mechanism allows for the local network to 
convey static policies.

-Jonathan R.

-- 
Jonathan D. Rosenberg, Ph.D.                600 Lanidex Plaza
Chief Technology Officer                    Parsippany, NJ 07054-2711
dynamicsoft
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http://www.jdrosen.net                      PHONE: (973) 952-5000
http://www.dynamicsoft.com

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From: Jonathan Rosenberg <[email-masked]>
Date: Fri, 03 Oct 2003 02:27:08 -0400

-Jonathan R.

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From: "Miguel A. Garcia" <[email-masked]>
Date: Fri, 03 Oct 2003 09:44:18 +0300

Inline.

Jonathan Rosenberg wrote:

> 
> 
> Miguel A. Garcia wrote:
> 
>> Hi:
>>
>> I would like to understand possible mechanisms to discover an MSRP 
>> relay in a network. Is this something that have been discussed before?
>>
>> When reading the MSRP draft, section 7.1.2, I found a discussion on 
>> the usage of DNS SRV when the MSRP client already knows the host name 
>> of the  MSRP relay. Fair enough. But in most situations this requires 
>> either provisioning or some out of band configuration. In a roaming 
>> scenario, when the network changes oftenly, the address of the MSRP 
>> relay may change as well. So I believe there is a need for a discovery 
>> mechanism of the MSRP relay.
> 
> 

I think both situations are possible: in one case, a client uses an MSRP 
relay in a roaming network. This could be the case of a hotel network. I 
believe DHCP will work fine here.

In another case, an MSRP relay is provided in a home network, and that 
MSRP relay is used no matter whether the user is attached directly to 
such network or indirectly through other networks. In this case DHCP 
won't obviously solve the problem.

> 
>>
>> If we compare with SIP, SIP uses DNS SRV records to solve this 
>> problem. The input to the DNS SRV query is a network name, and the 
>> answer is a host name. I was wondering if is this something that we 
>> can mimic in MSRP, as I believe the problem are pretty similar.
> 
> 
> The DNS SRV mechanism doesnt help you with local discovery of resources 
> (i.e., the ones in the network I just roamed into). 

If the client is aware of the network name, it will.

 > For that, we have
> been using a DHCP option code to return SIP servers. The analogy would 
> therefore be to learn MSRP relays from DHCP too. However, I think a 
> better model is to use DHCP to bootstrap a local access point (the SIP 
> server) and from there learn everything else. The use of a relay might 
> very well be something within the scope of a session policy that is 
> enforced by the local network. In that case, the static policy 
> mechanisms in the session policy draft:
> 

Certainly this is another solution. It also fits into Gonzalo's draft on 
the same subject:
http://www.ietf.org/internet-drafts/draft-camarillo-sipping-policy-package-00.txt

> would work. The registration mechanism allows for the local network to 

/Miguel

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From: "Miguel A. Garcia" <[email-masked]>
Date: Fri, 03 Oct 2003 09:44:18 +0300

Inline.

/Miguel