Subject: Re:

From: Rajan Pillai <[email-masked]>
Date: Thu, 13 Jan 2000 23:04:42 -0800 (PST)

What happens when User 1 sends an invite request to
User 2 and simultaneously User2 sends an invite
request to User 1 ? Do both accept each others'
connections - in which case, each receives 2 copies of
each message ?
__________________________________________________
Do You Yahoo!?
Talk to your friends online with Yahoo! Messenger.
http://im.yahoo.com

---

From: Jonathan Rosenberg <[email-masked]>
Date: Fri, 14 Jan 2000 09:56:42 -0500

What happens is what happens if they weren't simultaneous. User 1 makes
a call, then receives one. User 1 can accept the second if he likes.
Same for user 2. The result would be two separate calls (these will have
different Call-IDs as they are initiated by different parties). 

-Jonathan R. 

-- 
Jonathan D. Rosenberg                       200 Executive Drive
Chief Scientist                             Suite 120 
dynamicsoft                                 West Orange, NJ 07052
[email-masked]                     FAX:   (732) 741-4778
http://www.cs.columbia.edu/~jdrosen         PHONE: (732) 741-7244
http://www.dynamicsoft.com

---

From: Dean Willis <[email-masked]>
Date: Fri, 14 Jan 2000 10:30:42 -0600

> connections - in which case, each receives 2 copies of

My guess:

Same thing that happens when two cell phone users call each other
simultaneously, I suppose. One or both of them refuse to answer the incoming
call because they're busy placing a call.

Of course, display of the From: field in the user interface should allow the
user to detect this situation and apply whatever recovery heuristic they
prefer. Personally, I usually hang up, wait ten to thirty seconds, and call
again -- kind of like Ethernet collision backoff on a human scale.

--
Dean

---

From: Jonathan Rosenberg <[email-masked]>
Date: Fri, 14 Jan 2000 12:11:00 -0500

> again -- kind of like Ethernet collision backoff on a human scale.

It can even be done automatically:

SIP/2.0 500 Try Later
Retry-After: 30

-Jonathan R.

---

From: Thomas Marshall Eubanks <[email-masked]>
Date: Fri, 14 Jan 2000 12:10:30 -0500

> again -- kind of like Ethernet collision backoff on a human scale.

On my cell phone service, both callers will get busy signals and can then leave

simultaneous voice mail messages to the other. This exact situation happened to
me
yesterday ! It would be a useful feature to detect and short circuit this.

Regards

Marshall Eubanks

T.M. Eubanks
CTO
Multicast Technologies, LLC
P.O. Box 99
Clifton, Virginia 20124
Phone : 703-803-8141
Fax     : 703-222-3250
e-mail : [email-masked]

---

From: Jonathan Rosenberg <[email-masked]>
Date: Fri, 14 Jan 2000 12:33:01 -0500

> yesterday ! It would be a useful feature to detect and short circuit this.

An end system can do this; it doesn't require any protocol support.
Check the From field of the incoming call; if it matches the To field of
a call you have in progress, you are in this glare condition. Handling
is at the discretion of the end system. Any of the following are
supported now in SIP and are your choice:

1. answer so two calls are set up
2. return 500 with retry after
3. redirect to voicemail
4. detect the condition, cancel the call, and automatically answer the
call (might want to use a random timer before doing this so both sides
don't do it at the same time)

-Jonathan R.