Subject: A case related to "home Phone" type of functionality in SIP

From: "ANIRBAN ROY" <[email-masked]>
Date: Thu, 06 Jan 2000 09:25:43 +0530

hi,
I am trying to figure out how to get a home phone functionality in SIP.
The home phone has the following functionality
1    When a call comes all phones in the home ring
2    When one picks up, all other line must stop ringing
3    A user can picks up from any other telephone in the home and join
an existing call.

                                this a scenario where A calls a Home
Phone which has Three connection B, C, D in his home

+-------------|
                                                    A---------------|
Proxy        |---------------D

|                    |

+------------+

/     \

/       \

/         \

/           \

B           C

When a calls to a home phone which has 3 connection (B, C, D) lands on
proxy, then proxy forks the INVITE message to B, C, D. so every phone
starts ringing. This is the first character of Home Phone. Now Let's say
B picks up the phone then Proxy sends CANCEL message to C and D so that
the ringing can stop. This fulfills the Second point of Home Phone.

I am not able to get the call flow for the Third point in home Phone. If
lets say C picks up the phone then he should also be in session with A
and B. How can this be done because When a CANCEL message is received by
C and D then they both reached the state where they can only expect
INVITE.

Can any one please tell me how the call flow for the third point in the
home phone.

The above points of Home phone were taken from the -----Bell Labs
Journal (October-December 1998)

regards
Anirban

---

From: Dean Willis <[email-masked]>
Date: Thu, 06 Jan 2000 16:21:22 -0600

In a business environment, we call this a "single line extension".

SIP approaches tend to have the property that each phone is uniquely
addressed, whereas in the PSTN each circuit is uniquely addressed.

The obvious solution is to combine a parallel search proxy and some UAS
behavior.

The sequence is:
1) Incoming call reaches parallel proxy.
2) Parallel proxy invites all UASes in extension group.
3) User answers one extension.
4) Parallel proxy cancels unanswered legs. Those phones stop ringing.
5) Answering phone send INVITE to other phones in group, with "NO RING"
specified somehow, and long expire timer.

Case 1: 2nd party answers at extension phone:
6) First answering phone bridges all call legs

Case 2: User hangs up answering phone
6) Answering phone CANCELS open INVITES to other phones in group
7) Answering phone BYES all active call legs

Case 3: 3rd party places call to extension phone
6) Extension phone rings, ignoring open INVITE from first answering phone or
leaving it "attached" to a line button

etc.

Another approach is to use a chained INVITE, which has been propsed using
INVITE with Also headers, along with a conferencing bridge:

The sequence here is:
1) Incoming call reaches extension group proxy
2) Extension group proxy INVITES or extension bridge, with an Also: or
whatever header for each phone in extension group
3) Extension bridge INVITES each phone in group
3) User answeres one extension
4) Extension bridge OKs call leg to user
5) Extension bridge OKs call from caller
6) Exenstion bridge CANCELS legs to other phones in group
7) Extension bridge reINVITES other phones in group with a "NO RING" option
and long expire timer.
. . .
with similar tear-down and 2nd call scenarios

And there are dozens of other variations on these themes possible.

--
Dean

> -----Original Message-----
> From: [email-masked]
> [mailto:[email-masked]]On Behalf Of ANIRBAN ROY
> Sent: Wednesday, January 05, 2000 9:56 PM
> To: [email-masked]
> Subject: A case related to "home Phone" type of functionality in SIP
>
>
> hi,

---

From: Magnus Ahltorp <[email-masked]>
Date: 07 Jan 2000 06:55:29 +0100

> 3    A user can picks up from any other telephone in the home and join

The third point is not always a feature of a home phone system. For
example, in Sweden, the default is a priority system, where the phones
are connected in serial, and only one phone at a time can be in use.
This is supposed to make it harder for people to listen in to other
people's calls.

I would rather want a dial tone in my ear when I lift the phone in
point three, for convenience and privacy.

/Magnus