Subject: RE: [SIP] Attempt at summarizing current SIP drafts (SIP Mobility )

From: "Roy, Radhika R, ALCOO" <[email-masked]>
Date: Thu, 5 Oct 2000 11:12:42 -0400

Hi, Billy:

I guess that you have answered (i.e., clarified) most of the questions:

1. You are right that no new extension is needed using re-registration and
re-INVITE messages. So, people will be allowed to use these procedures. If
this is accepted, I assume that a significant milestone has been achieved
(by default, SIP becomes a mobility-aware application).

Once we accept this basic fact, people can go back to see what additional
things need to be done (some I-Ds are there), if any (may need some minor
extensions in SIP as well as some I-Ds suggest).

2. Hand-off is an area to see the impact in the SIP session layer. It is
primarily the performance aspect of it. (It is inherent problems for all
layers in the case of mobility).

3. Some (minor) extensions may be needed as I mentioned in item 1 (some I-Ds
have been proposed, but more can be looked into).

4. Logical call flows may not change at all (something similar to call
transfer and/or adding a new party in the call during the creation of ad hoc
conference call) to take care-of the hand-off situation.

5. It is not whether the idea is good or bad. It is a basic need of the
users to address the issues while the point of attachment changes during the
SIP session.

Best regards,
Radhika R. Roy
AT&T

-----Original Message-----
From: Billy Biggs [mailto:[email-masked]]
Sent: Thursday, October 05, 2000 10:37 AM
To: Roy, Radhika R, ALCOO
Cc: Arnoud van Wijk (ELN); 'hammer michael'; Brian Stucker; Rohan Mahy;
[email-masked]
Subject: Re: [SIP] Attempt at summarizing current SIP drafts (SIP
Mobility )

  Hi Radhika,

> The fact of the matter still remains true that the address information
> in the register needs to be updated and one may still like to use the
> re-INVITE messages to the new addresses. If this solution is
> acceptable to anyone, let us allow them to use it.

  I'm still confused about what you are asking.  I don't think anyone is
disallowing you to use this mechanism.

  Are you asking:

  1. What extensions to the SIP REGISTER and INVITE transactions are
     required to support active session mobility?

     The consensus on this list seems to be that no extensions are
     required.  Please correct me if I am wrong.  We've already
     established that the Contact address can be updated in a re-INVITE,
     and I believe this is in the bis.

     If you deployed a system which used this form of mobility, I
     believe you would have no problems interoperating with others.

  2. What technical problems are there with this solution?

     Many people have mentioned hand-off time as being a factor, I'd
     estimate having an upper-bound for a successful change to be about
     half a minute.  Another problem would be handling un-succcessful
     hand-offs: what if the other end does not accept the INVITE?  The
     call would likely be disconnected if the mobile user cannot remain
     at the old address.

  3. What extensions can we propose to solve these problems?

     Building a mobile-IP phone that updates the session only as an
     optimization might be worth pursuing.  However, I still don't see
     any work which may lead to extensions to SIP.  I think we have
     everything we need.

  4. What is the specific call-flow for a SIP session hand-off?

     If you're asking "how do I do it", I believe this has come up
     before on the list, and I would recommend searching the archives.
     Regardless, this is simply an afternoon research project.

  5. Is it a good idea?

     This is what I believe most people have been answering.  As I've
     mentioned before, I don't think it's a good idea.  However, that
     shouldn't stop you from researching it.

-- 
Billy Biggs                    [email-masked]
http://www.div8.net/billy/           [email-masked]

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---

From: Henning Schulzrinne <[email-masked]>
Date: Thu, 05 Oct 2000 11:41:23 -0400

I don't want to wade too deeply into this discussion, but just note that
in many of today's networks, we don't have inter-network mobility
between calls. Try asking your local ISP to give you a permanent IP
address and run a HA for you... Permanent device IPv6 addresses will
presumably be used in 3GPP, so that's not a real deep concern there.

In general, from an efficiency perspective, mobile IP, as available
today (as opposed to the micro-mobility proposals, which are
significantly better), has equivalent or worse update latencies, as any
binding updates go to from the MH to the HA and then to the CH, even
ssuming that the correspondent host supports binding updates (no common
OS do, as far as I know).

Thus, I believe that for low-latency audio, mobile IPv4, as currently
(barely) available, is not good enough and application-layer mobility
can do better. That is likely to be a transient situation, however.

Even in the longer-run, if we want hand-offs between two non-cooperating
networks (e.g., a UMTS network and my university network), there may
well be a role, by necessity and as a fallback solution, for
application-layer mobility.

As long as you can keep your same IP address (modulo the current
practical IPv4 mobility problems), I would use IP mobility, for
generality. If that's not an option, it's nice to know that SIP can help
out to at least keep your voice or video call up, even if you need to
restart your web browser and if your telnet connection goes dead.
-- 
Henning Schulzrinne   http://www.cs.columbia.edu/~hgs

---

From: Michael Thomas <[email-masked]>
Date: Fri, 6 Oct 2000 12:08:22 -0700 (PDT)

This seems eminently reasonable to me.

	   Mike