Subject: [SIP] REFER revision

From: Robert Sparks <[email-masked]>
Date: Fri, 2 Feb 2001 17:33:03 -0500

Here is REFER using NOTIFYs from implicit Subscriptions
to get around the transaction timeout problem. I've submitted
this to the draft repository, but wanted to get it into
the hands of those attending next week's meeting as early
as I could.

RjS

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From: Takumi Ohba <[email-masked]>
Date: Tue, 6 Feb 2001 18:50:45 +0900

Dear all,

This is Takumi Ohba, NTT.
I have some questions concerning handling of over-length messages.

One example;
If a user want to attach very large data to a SIP message as a MIME part,
but it make the message longer than the MTU, what should the user do?
The only choice to the user is to give up attaching the data?

Another example;
A SIP proxy may receive a larger message that it can transfer.  This may
happen when the proxy uses different transport layers for incoming and
outgoing links and the outgoing link has smaller maximum datagram packet
size than that for the incoming link.
For example, the incoming link uses UDP (max: 64k octets) and the outgoing
link uses signalling AAL (max: 4k octets).  The proxy may receive 5k-octet
message if the MTU permits it, but it cannot transfer the message to the
outgoing signalling AAL link.

In this case, what should the proxy do?
Should it give up transferring the massage itself, or shorten the message
and transfer it by discarding less important part of the message?  In the
latter case, how can the proxy identify less important part of the message?

Best regards,
Takumi Ohba

***************************************************
Takumi OHBA
NTT Network Service Systems Laboratories
tel +81 422 59 4405  fax +81 422 59 3494
e-mail [email-masked]
***************************************************

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From: Christer Holmberg <[email-masked]>
Date: Tue, 06 Feb 2001 16:50:42 +0200

Hi,

I think it has been agreed that a SIP message, including possible MIME
message bodies, should "fit" into a single UDP MTU. Do you have an
example where that length would not be enough?

Regards,

Christer Holmberg
Ericsson Finland

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From: Takumi Ohba <[email-masked]>
Date: Wed, 07 Feb 2001 06:34:57 +0900

Dear Holmberg,

Thank you for your reply.

In my understanding, a SIP message may include user-to-user information, suc
h as an image file.
Such information can be very large, say 100k byte or more.

In addition, some transport layer protocols have poorer max length than UDP.

I think that SIP needs explicit specification for handling of over-length me
ssage, or I don't think this is a good idea but SIP should specify simple me
ssage segmentation procedures like as ISUP.

Comments?

Regards,

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From: Henning Schulzrinne <[email-masked]>
Date: Tue, 06 Feb 2001 16:42:12 -0800

> ssage segmentation procedures like as ISUP.

We have a protocol called TCP for that. The sender should know, to
reasonably degree, what the max. message size is and switch to TCP as
needed (or SCTP, if that floats your boat). For very long responses, the
UAS can redirect to a transport=tcp URL.

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From: "Eric Burger" <[email-masked]>
Date: Wed, 7 Feb 2001 20:55:40 -0500

His point wasn't that it wouldn't fit into a UDP MTU, it's that it might not
fit into an ATM MTU, for example.

How's this for a scenario: lots of VIA's and computer generated URL's.  That
will pretty quickly fill a 4K ATM AAL5 MTU, or even the "safe" 540 byte UDP
WAN MTU.

Reminds me of the "how big should my buffer be" thread...  The answer is
"boundless".

> -----Original Message-----
> From: [email-masked]
> [mailto:[email-masked]]On Behalf Of Christer Holmberg
> Sent: Tuesday, February 06, 2001 9:51 AM
> To: Takumi Ohba
[snip]
> example where that length would not be enough?
[snip]