Subject: [Sipping] RE: Comments on PoC drafts

From: "Andrew Allen" <[email-masked]>
Date: Fri, 4 Mar 2005 11:19:18 -0500

Christian

Sorry I missed the other questions.

More responses below.

Andrew

________________________________

From: Schmidt Christian [mailto:[email-masked]] 
Sent: Wednesday, March 02, 2005 9:34 AM
To: [email-masked]'; Andrew Allen;
[email-masked]'; [email-masked]
Subject: Comments on PoC drafts

Hallo, 

after a first review of both drafts, here first comments / questions /
proposals. 

draft-garcia-sipping-poc-isb-am-01.txt 
"This document defines a SIP event package to support publication,
subscription and notification of additional capabilities required by the
PoC service.  This SIP event package is applicable to the PoC service
and may not be applicable to the general Internet."

draft-allen-sipping-poc-p-headers-01.txt 
"This document describes a set of private Session Initiation
Protocol(SIP) headers (P-headers) used by the Open Mobile Alliance
OMA),For Push to talk over Cellular (PoC) along with their
applicability, which is limited to the OMA PoC application.  The
P-headers are used for requesting and indicating the alerting mode of
the handset which is particular to the PoC application."

General issues: 

*	What is the correlation of the two drafts? Are they independent?
Are they describing independent requirements / solutions for PoC?
*	What is the exact meaning behind the applicability restriction
within the Internet? Perhaps it would be better to include the
preconditions for applicability in this case.

draft-allen-sipping-poc-p-headers-01.txt: 

*	The usage / handling of the new SIP private headers in the
different entities become not clear. An example (PoC Group Call) could
help for understanding the use case and the need for the new headers and
should be added.

We will consider adding an example call scenario in the next version as
you suggest.

	*	Calling PoC terminal -> PoC Server: INVITE with
P-Altering-Mode header: Auto-Answer.
	*	PoC Server -> Called PoC terminals 1-n): INVITE with
P-Altering-Mode header: Auto-Answer.
	*	Called PoC terminal x: 200 Reply: P-Answer-State header
"unconfirmed response"

Normally the PoC Server would return the P-Answer-State header with the
"unconfirmed response" as an indication that it has not yet contacted
the terminating PoC terminal. A terminal would normally not do this.

	*	PoC Server -> Calling PoC terimal: 200 Reply:
P-Answer-State header "unconfirmed response"
	*	The 200 responses from other called PoC terminals are
not forwarded by the PoC Server to the Calling PoC terminal.

Correct once a 200 OK is sent to the calling terminal all further
responses from other terminal are blocked by the PoC server from the
calling PoC Terminal to PoC Server dialog (as per RFC 3261)

	*	After receipt of the 200 Reply with "unconfirmed
response", the calling PoC terminal can signal to the subscriber, that
in theory somebody could listen to his talk.

Yes the terminal may provide an indication to the caller to talk and
then the PoC server can buffer the speech until the called terminal
answers.

	*	Are the assumptions correct?

The one misunderstanding is that the PoC terminal does not send the
"unconfirmed response".

*	Is it possible for a PoC terminal to signal to the PoC server a
change in the answering mode, independent from call activities.

A method for doing this is specified in draft-garcia-sipping-isb-am

*	Would it be possible for the calling PoC terminal, to derive the
kind of response from the period between INVITE and 200 reply?

I don't think this would be a reliable solution to the problem as it
depends on the round trip times that can vary considerably depending on
the bandwidth of the access network (such as wireless) and the number of
domains transversed. Also there may be more than one Poc Server involved
in the session establishment and the PoC Server in the domain of the
called party may signal to another PoC server that acts as the focus for
the session the unconfirmed response so that the focus can perform the
buffering.

Some editorial comments: 
draft-garcia-sipping-poc-isb-am-01.txt 

*	1. Introduction / 3. paragraph: This is mode of operation > This
mode of operation.
*	1. Introduction / Last paragraph: Difficult to read, please
rephrase.

draft-allen-sipping-poc-p-headers-01.txt: 

*	4.1.1 Requirements / AM2: a manual answer mode which allows
requires the invited.. > a manual answer mode which requires the
invited..
*	4.1.4 Usage of the P-Alerting-Mode header:  At the location of
the first usage of MAO, the abbreviation should be explained.

Regards 
Christian Schmidt, Siemens COM 

        Phone:  +49 89 636-75192 
        Mobile:         +49 178 7700363 
        Fax:    +49 89 636-75577 
        E-Mail:         [email-masked] 

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From: "Andrew Allen" <[email-masked]>
Date: Fri, 4 Mar 2005 11:03:37 -0500

Christian

Thanks for the input.

Responses inline.

Regards

Andrew

Hallo, 

General issues: 

I concur with Minguel's response that these two drafts are independent
from an IETF and SIP point of view. However the OMA push to talk project
depends on both of these drafts.

Again I concur with Miguel's response that the meaning is that these
documents contain a bunch of assumptions, specified in the PoC
documents, that we believe make these documents not generally applicable
to the Internet.

Some editorial comments: 

This editorial error will be corrected in the next version

I will spell out and explain MAO (Manual Answer Override) before using
the abbreviation in the next version

Regards 

        Phone:  +49 89 636-75192 
        Mobile:         +49 178 7700363 
        Fax:    +49 89 636-75577