Hi Juha,
You are absolutely right in both of your claims:
- In "pure" SIP the registration is only needed to make the incoming
requests to find you. You don't need it for sending requests out.
- If you use 3G network only as "access to the Internet", you can send your
requests to whichever proxy you want, and there is no way for the operator
to prevent it. (Of course the operator can try to deny proper QoS for your
media flow in that case.)
However, Keith and me are referring specifically to 3GPP Release 5 IP
Multimedia Subsystem (IMS). IMS is one way to offer SIP-based multimedia
services in 3G networks, and it has some optimizations for radio and it is
designed for large scale use.
There are two technical reasons why registration is required before issuing
outgoing requests in IMS.
1. During the registration the user is assigned a serving SIP proxy in the
home SIP domain, to which all requests are forwarded by an outbound proxy
(which you find with DHCP etc.) in the visited SIP domain. This proxy
provides "originating" services for the sessions (filtering, pre-paid etc.),
and can route requests via application servers for that. During registration
user's service info is downloaded to that proxy.
2. The user is authenticated during registration, and he is assigned keys to
be used for further outgoing requests. This saves some RTTs/signaling
compared to authenticating each request separately. I think this is still
somewhat open in the standardisation (problems with replay attacks etc.), so
the point is not as definite as the first one.
In a way you could say that both 1 and 2 are about optimization, but I think
you need it to build large scale systems. I'm not saying 3GPP's choises are
better than something else, but they have their reasons.
What comes to SIP protocol: Based on Jonathan's answer to my question I take
there is no response for "Registration Required".
Markus
> -----Original Message-----
> From: ext Juha Heinanen [mailto:[EMAIL PROTECTED]]
> Sent: 29 March, 2001 16:04
> To: Drage, Keith (Keith)
> Cc: [EMAIL PROTECTED]; [EMAIL PROTECTED]
> Subject: RE: [SIP] Response if user not registered?
>
>
> Drage, Keith (Keith) writes:
>
> > Because in 3GPP at least, the act of registration
> identifies the proxy that
> > will support all calls for that user, both incoming and
> outgoing (i.e.
> > outbound proxy), and the privileges or service
> capabilities that user has,
> > e.g. the act of registration tells the outbound proxy that
> the user can make
> > outgoing calls.
>
> i don't get it. what do you mean by registration identifying a proxy?
> registrat and outbound proxy can be two totally different entities and
> there are many means available (e.g. dhcp) to find each. i can't
> understand, how 3gpp force a user to use a particular registrat or
> outbound proxy. if 3gpp provides ip access, the user is able to elect
> to use sip services provided by anybody.
>
> when i make a call, the outbound proxy can authenticate me and thus
> learn who i am. what i'm allowed to do can be described in a user
> database that the proxy can consult. this user database may not have
> anything to do with hlr or whatever the 3gpp database is.
>
> it is high time to let the mobile user loose so that he/she can select
> all services (including telephone) independently from
> wireless internet
> access provided by 3gpp. i moved this discussion to sip-implementors,
> since it hardly has anything to do with sip protocol itself.
>
> -- juha
>
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