Re: [MEDIACTRL] Call Flows Document

["Even, Roni" <[e-mail]>]

Hi,

I can accept Mary's comments.

 

My humble input is that the current ecs document cannot serve as a
starting point, it is not just a media control example flows document.

I assume we want to have basic call flows examples yet the document does
not supply simple examples but goes to a detailed analysis of the media
control architecture based on the authors interpretation.

 

The comments are partial and do not even address the syntax of the
examples. I accept that other people will review the ecs draft before we
can decide if this is a good start for a WG document.

 

The abstract of the document says that this is not just call flows.

"It aims at being a simple guide throughout the use of   the interface
between Application Servers and MEDIACTRL-based Media  Servers, as well
as a hopefully helpful base reference documentation  for both
implementors and protocol researchers."

 

Section 4 is not relevant to call flows since it describes an
implementation

 

Even though the document claims to have simple call flows it goes to
high details based on a specific implementation, the text is not
describing the flow but gives interpretation of the normative text in
the framework document

 

Figure 6 and the text describes one way to establish 3pcc and not the
media control flow. 3pcc is described in other RFCs and there is more
than one way to do it.

 

Echo test is not related to the media control call flows.

 

The phone call scenario starts with a SIP 3pcc  flow describing 3pcc and
the whole example is not a typical AS-MS call flow. In figure 20 it
shows the flow of the media control but missing the step where the UA
using SIP connects to the MS. This is important since we have assumption
that the Mediactrl JOIN arrives before the SIP invite

 

Roni

 

 

 

 

From: [e-mail] [mailto:[e-mail]] On
Behalf Of Mary Barnes
Sent: Thursday, July 31, 2008 12:00 PM
To: Eric Burger; [e-mail]
Subject: Re: [MEDIACTRL] Call Flows Document

 

Thanks for the detailed (and accurate) summary of this issue. My
responses are below [MB]. 

 

Mary.

 

________________________________

From: [e-mail] [mailto:[e-mail]] On
Behalf Of Eric Burger
Sent: Wednesday, July 30, 2008 12:48 PM
To: [e-mail]
Subject: [MEDIACTRL] Call Flows Document

At the meeting today, we discussed at length the issues around adding
<http://www.ietf.org/internet-drafts/draft-miniero-mediactrl-escs-02.txt
>, "Media Control Channel Framework (CFW) Call Flow Examples" as a work
group item. 

 

To recap:

1. Just about everyone stated it is extremely useful to have call flows.

   a. Important for us as protocol developers to debug the
specification,

      e.g., "Oops - we forgot that message"

   b. Important for some developers with interpretation of the
specifications

   c. Important for interoperability testing

 

2. Many people pointed out call flow documents have their drawbacks.

   a. Some people will code to the call flows and not to the
specification.

      i.  If the call flows are wrong, the developer will code the wrong
thing.

      ii. Call flows cannot capture the nuances of the protocol, such as

          non-deterministic message order or legal, but not shown in a

          call flow, messages that pop up

   b. When people see a call flow document, they may not read the

      specification at all.

   c. When people see a Work Group *draft*, they may consider it to be

      a stable, authoritative reference. 

[MB] IMHO, there's not much we can do nor do we have much control over
any of the above - it is what it is.  I don't disagree at all that call
flows cannot at all capture all the normative details of the protocol
that must be implemented. However, for folks that are visual learners,
the flows are an invaluable guide to work one's way through the specs.
And, none of our specs are ever perfect and the flows can sometimes be a
source of identifying those bugs (even after publication).  [/MB] 

 

It would be safe to say that no matter what we decide here, there will
be a call flows document.  The questions to decide are:

 

1. What document(s) will we produce?  Will we produce:

   a. A basic call flows document, illustrating some examples of

      how the protocol works (see draft-ietf-sipping-service-examples-15

      for an example) 

[MB] IMHO, this is most important for now in developing in parallel with
the protocol and is an invaluable reference for implementations.   I
also do not believe that even with the flows you will NOT get identical
broken implementations from the flows as there are always gaps that must
be filled in based on the normative details in the protocol spec. [/MB] 

   b. A torture test document, illustrating examples of malformed

      messages or messages seriously out of order, that stacks

      must not barf on (see RFC 4475 for an example) 

[MB] I think it would be very difficult to produce this (and not
necessarily useful) until after there's been some basic interop testing
and folks can see what are the most common errors and perhaps add
variations of such. [/MB] 

 

   c. A test suite document, describing how to achieve interoperability

      (see
http://www.msforum.org/techinfo/approved/MSF-IA-SIP.015-FINAL.pdf)
<http://www.msforum.org/techinfo/approved/MSF-IA-SIP.015-FINAL.pdf>  

  

[MB] This seems to be something well beyond the completion of the
protocol and maturity of implementations.  And, maybe would be more of a
SIPForum activity.[/MB] 

   d. A plurality of a, b, or c

   e. All of a, b, and c

 

Note all call flow documents are Informational (not Normative) by
definition.

 

2. Will the work group produce these documents?  No matter what,
individuals

   from the work group will write the document(s), and people in the
work

   group (many have already volunteered) will review the document(s).

   a. Do they need to be Work Group documents? 

[MB] I honestly can see no problems in making them WG documents and alot
of positive reasons: folks pay more attention, the review is more
rigorous (by all review teams AFAIK) and it acknowledges the work done
by authors/editors. [/MB] 

   b. Is it OK for them to be Individual documents, for now. 

[MB] In my view, as long as we get a milestone for 1a, then I'm not so
concerned. I did speak to Roni after the meeting and I believe his
concern over inconsistencies between the protocol and the current call
flow document are valid and should be addressed and if it makes the WG
more comfortable having this done prior to adopting as a WG document,
that's okay.  There is precedence in the past to adopt a document with
an agreement to update per WG input and concerns.  [/MB]

 

 

Please RSVP with your views on the above questions.

 

Thanks.

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