For both GRUU and Outbound a given instance-id (+sip-instance) actually
represents a single UA contact instance rather than just a single User Agent.
The basic idea behind GRUU is that a request addressed to a GRUU is forwarded
by the proxy to a specific Contact address. The goal is the same with Outbound
but it adds multiple flows/paths to that UA Contact. This is reflected in the
proxy procedures in both GRUU and Outbound.
In both cases, the proxy does serial forking to Contacts with the same
instance-id.
For GRUU it starts with the most-recently registered binding (according to
section 6.1 of GRUU):
The proxy MUST select the most recently refreshed
contact. As with draft-ietf-sip-outbound, if a request to this
target fails with a 408 (Request Timeout) or 430 (Flow Failed)
response, the proxy SHOULD retry with the next most recently
refreshed contact. Furthermore, if the request fails with any
other response, the proxy MUST NOT retry on any other contacts
for this instance.
For Outbound, it attempts the registered flows (according to section 7 of
Outbound):
When a proxy uses the location service to look up a registration
binding and then proxies a request to a particular contact, it
selects a contact to use normally, with a few additional rules:
o The proxy MUST NOT populate the target set with more than one
contact with the same AOR and instance-id at a time.
o If a request for a particular AOR and instance-id fails with a 430
(Flow Failed) response, the proxy SHOULD replace the failed branch
with another target (if one is available) with the same AOR and
instance-id, but a different reg-id.
o If the proxy receives a final response from a branch other than a
408 (Request Timeout) or a 430 (Flow Failed) response, the proxy
MUST NOT forward the same request to another target representing
the same AOR and instance-id. The targeted instance has already
provided its response.
Therefore, a User Agent that is registering multiple Contacts to allow the
possibility of parallel forking would need to have a separate instance-id for
each Contact.
For User Agent's that have multiple interfaces, it could use the MAC address of
each interface to create a unique UUID URN for each contact.
Thus, the following scenario is possible:
UA_Contact_wlan;+sip-instance=ID_1;reg-id=1 ----- OB_1 ----- REG_1
UA_Contact_wlan;+sip-instance=ID_1;reg-id=2 ----- OB_2 ----- REG_2
UA_Contact_3g;+sip-instance=ID_2;reg-id=1 ----- OB_1 ----- REG_1
UA_Contact_3g;+sip-instance=ID_2;reg-id=2 ----- OB_2 ----- REG_2
Unfortunately, the current text in section 4.1 says that a UA has "an Instance
Identifier".
cheers,
(-:bob
-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Christer Holmberg
Sent: Monday, October 13, 2008 3:45 PM
To: Juha Heinanen; [email protected]; Paul Kyzivat; Dean Willis
Subject: Re: [Sip] Dual registration without Outbound
Hi,
>>the proxy does not, but i don't want to complicate
>>configuration of the UA simply in order to cope with the
>>brain damage of ob draft. also, don't want that the UA
>>has to send two invites for one contact each.
>
>typo: i don't want that the UA has to send two REGISTERs for
>one contact each. that is, UA must be able to register both
>of its contacts in a single register request.
You will still have to send a REGISTER for each flow that you establish
- no matter whether you use the same contact/instance-id or not.
Or, do you also want to change outbound so that you can establish
multiple flows with a single REGISTER?
Regards,
Christer
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