Section 6.2 of this RFC specifically provides for a UA to advertise
this state "prior" to sending the INVITE. I have cut and pasted the
relevant verbiage from 4235 for your perusal.
"The following example shows how a SIP telephone user agent can
provide detailed state information and also emulate a shared-line
telephone system (the phone "lies" about having a dialog while it is
merely offhook).
The MLA draft pretty much uses the same.
Thanks
Venkatesh
On Fri, Mar 21, 2008 at 1:39 PM, Francois Audet <[EMAIL PROTECTED]>
wrote:
The trying state in RFC 4235 is ok (that's after the INVITE). No
ptoblems there.
It's the line seize BEFORE sending an INVITE that is a problem.
From: Venkatesh [mailto:[EMAIL PROTECTED]
Sent: Friday, March 21, 2008 13:35
To: Audet, Francois (SC100:3055)
Cc: Bill Mitchell; [email protected]
Subject: Re: [BLISS] MLA with Floor Control
Francois:
The dialog state RFC 4325 specifically provides a "trying" state to
indicate a state where a call is about to be initiated. We are
simply using this state to indicate origination of a new call
request.
Thanks
Venkatesh
On Fri, Mar 21, 2008 at 1:19 PM, Francois Audet <[EMAIL PROTECTED]>
wrote:
I really believe that this whole idea of "line seizure" is
completely out-of-line with the SIP model.
If we do something like that, we are completely changing the nature
of SIP and making it a stimulus control protocol like MGCP (or the
old proprietary Phone control protocols used by many vendors,
including my employer).
If we go in that direction, we would need to redefine what "on the
phone" means, so that instead of "in a session", it would mean "off-
hook". Every single INVITE would now be preceded by a PUBLISH of
some "off-hook" status. This would not only hamper significantly
scalability of SIP, but would make it a different protocol.
What's next? Cursor control? Bitmap screen control?
If one wants a blast from the past with these types of features, one
should stick with protocols from the past.
I am completely opposed to changing SIP to be a stimulus protocol.
From: Bill Mitchell [mailto:[EMAIL PROTECTED]
Sent: Friday, March 21, 2008 12:55
To: Audet, Francois (SC100:3055)
Cc: [email protected]
Subject: RE: [BLISS] MLA with Floor Control
Completely agree that line seizure upon line-key-selection is
complex, but the idea behind line seizure over SIP was to minimize
complexity. We've heard that customers want the functionality for
shout control. And issues like line key hogging can be
addressed with a proper implementation.
My terminology wasn't quite right. I should have said "Line seizure
post-line-key-selection" is not worthwhile. If the client is going
to render a UI based on the line #, for purposes of shout-control,
then "Line Key Hopping" will occur. When a user has selected a line
key and is dialing, an Inbound call will force a change in line key
usage, as will an outbound call placed from a different phone. I
see this as unacceptable to most users.
From: Francois Audet [mailto:[EMAIL PROTECTED]
Sent: Friday, March 21, 2008 12:15 PM
To: Bill Mitchell; DOLLY, MARTIN C, ATTLABS
Cc: [email protected]; [EMAIL PROTECTED]
Subject: RE: [BLISS] MLA with Floor Control
It's not POST call-setup. It's AT call setup.
It's the difference between:
Line seisure by pressing key
User press Line appearance. This is reported to Presence/Dialog
server. PUBLISH or BFCP.
Presence/dialog for that line goes "busy" right away, for anybody
that sees it
Nobody can use that line regardless of how long it takes the user to
dial
Line seisure at call setup
User press Line appearance. This is local: no reporting anywhere.
Nothing changes anywhere
Line is "seized" when the call is actually made
In the interim between pressing the key, somebody else could also
press the key and make a call. If he's faster, he'll be able to
seize the line before the first guy.
Besides the mind-numbing complexity of doing the first approach,
there are also advantages to the second approach. It avoids the
problem of having somebody "hogging" the line by pressing on the key
and not dialling anybody.
And frankly, the SIP mechanism to "arbitrate" the line-seisure-by-
pressing-an-appearance will by definition be very complicated and
generate lots of traffic. I don't be believe it will be simpler than
BFCP.
Furthermore, there will be lots of potential for race condidtions
(while the NOTIFYs and PUBLISH are flying all over the place). This
will result in very poor user experience. Basically, pressing on the
button will often "not work". (I have a vision of pissed-off users
repeatedly pressing the key that doesn't want to turn on, and
banging on their sets).
The second option, with line seisure at call setup does not suffer
from this problem. The expectation is that the line is "taken" when
you actually make the call, not when you press the button.
I will point out that PBXs (as opposed to key systems) often work
the second way, not the first way.
This is all very similar to arbitrating between making an outgoing
call and receiving an incoming one while dialing.
From: Bill Mitchell [mailto:[EMAIL PROTECTED]
Sent: Friday, March 21, 2008 11:58
To: DOLLY, MARTIN C, ATTLABS
Cc: [email protected]; Audet, Francois (SC100:3055); [EMAIL PROTECTED]
Subject: RE: [BLISS] MLA with Floor Control
My answer is YES. Line seizing before call setup is worthwhile,
because it enables shout control with a **reasonable end-user
experience**.
Line seizing post-call-setup is NOT worthwhile. It only adds
confusion with potential mid or post-dial line key hopping.
Pre-call-setup line seizure can be optional.
BFCP has the right primitives, but I firmly agree with Venkatesh
that it adds significant network complexity and would be a large
barrier for implementation. I'll add my vote for a SIP-
based mechanism to communicate line seize requests and responses.
-Bill
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On
Behalf Of DOLLY, MARTIN C, ATTLABS
Sent: Friday, March 21, 2008 9:09 AM
To: Francois Audet; Venkatesh; Paul Kyzivat
Cc: Rohan Mahy; [email protected]
Subject: Re: [BLISS] MLA with Floor Control
I agree, NO
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On
Behalf Of Francois Audet
Sent: Friday, March 21, 2008 11:45 AM
To: Venkatesh; Paul Kyzivat
Cc: Rohan Mahy; [email protected]
Subject: Re: [BLISS] MLA with Floor Control
The real question is "should we do line seizing before call setup"
as a worthwile feature.
I think "No".
If the group feels "Yes", then we could look at BFCP. I really think
we should not be stupid enough to make this mandatory.
From: Venkatesh [mailto:[EMAIL PROTECTED]
Sent: Thursday, March 20, 2008 21:49
To: Paul Kyzivat
Cc: Audet, Francois (SC100:3055); Rohan Mahy; [email protected]
Subject: Re: [BLISS] MLA with Floor Control
I don't disagree with your argument. However, I also think, should a
particular approach unduly complicate implementation of a feature
(especially require support from multiple network elements for a
feature to work), vendors are going to resort to non standard ways
to implement the feature as well......
Venkatesh
On Thu, Mar 20, 2008 at 9:15 PM, Paul Kyzivat <[EMAIL PROTECTED]>
wrote:
I'm not promoting one way or the other. Ultimately people building
products will build the functionality they think they need to sell
their
products. If people feel this is important then they will want a way
to
do it. If it isn't standard then it will be nonstandard.
Paul
Francois Audet wrote:
>
>
>> There is a tradeoff...
>>
>> If multiple extensions can place outgoing calls from the same
>> line, then the line doesn't have "binary" status, so it can't
>> be indicated as active or not with a light. And you can't
>> "conference in" by picking up on the same line.
>>
>> While I am not into it myself, I can see how someone can
>> build a "business process" around the specific way in which
>> lines are managed by the phones, and then be very upset if
>> they can't get that same user experience.
>
> Yeah, sure, it's doable. I do not believe that adding the concept
> of a Line number to do this is required to do this, or even
> desireable.
>
>> Now you can come up with some very nice UIs that provide
>> better user experience, if you have a suitable display
>> instead of just a bunch of lights. (E.g. an entry for the
>> "number" (AOR that people call), and a variable length drop
>> down list of active calls, showing the callerid of the
>> caller, how long it has been active, and which
extensions are
>> currently connected to it.) But that is *different*, and
>> requires a device with richer UI.
>
> Agreed.
>
> My point is that we shouldn't bastardize the protocol with all this
> complex extra protocol (Line numbers, BFCP, NOTIFY/PUBLISH-storms,
etc.)
> just do do this.
>
> The basic "single-lamp" based approach is doable without any of
this.
>
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