From: linneweh@rtsg.mot.com (Louis Linneweh)
Newsgroups: comp.dcom.telecom
Subject: Re: Questions About Call Waiting
Date: 10 Apr 92 15:51:44 GMT
Article-I.D.: eecs.telecom12.313.9
Organization: Motorola Inc., Cellular Infrastructure Group
X-Submissions-To: telecom@eecs.nwu.edu
X-Administrivia-To: telecom-request@eecs.nwu.edu
X-Telecom-Digest: Volume 12, Issue 313, Message 9 of 10

pdh@netcom.com (Phil Howard) writes:

> How does call waiting behave if:

How call waiting behaves depends upon when the original call can be
considered "stable" (or "in conversation state") for the party being
waited on.  If both parties of the original call are served by the
same switch this normally means the call must be answered.  (Remember
that the ringback tone comes from the called office, but in this case
that is the same as the calling office, so both parties will have
state changes when the called party answers, after which the call is
stable.)

If the call is between switches, the calling party of the original
call will (by most types of switches) be considered stable upon
completion of outpulsing and placed in conversation state (to listen
for call progress tones from the distant end).  Therefore, call
waiting is active during distant: ringback tone; busy signal; recorded
announcement; etc.  With SS7, some of these call progress tones (e.g.
busy or network congestion tone or announcement) may be given locally
(at the calling party's switch) so the call would not be considered
stable.  In other implementations, answer supervision is required, so
un-answered calls will never be interrupted by call waiting.

So now the answers:

> 1.  the called party is ringing from another caller calling them?

The party trying to call wait on a ringing line will get busy tone.
(The called party is not in a stable conversation state, so call
waiting is not active.)

> 2.  the called party is calling someone else and they are getting and
>     that call is ringing?

If the original call is intra-office (to someone served by the same
switch) the original calling party is not yet stable (getting local
ringback tone) and the call waiting attempt will result in busy (call
waiting not yet enabled).  If the original call was inter-office, most
switches will consider the calling party of the original call stable
and enable call waiting immediatly after outpulsing, so call waiting
notification can interrupt distant call progress tones, including
ringback tone.  The waiting party will hear ringback tone.  (Other
implementations require answer, so the waiting party will just get
busy tone.)

> 3.  the called party is calling YOU at the same time?

Intra-office: both get busy tone.  Inter-office: called party gets
busy tone; if your call arrived before he finished outpulsing, you get
busy tone; if after, you get ringback tone and the called party gets
call waiting allert interrupting busy tone.  (Or both get busy tone if
the implementation requires answer.)

> 4.  same as #3 and you also have call waiting?

Intra-office: both get busy tone.  Inter-office: both could get call
waiting, but more likely is one will get busy tone interrupted by the
call waiting alert of the other who hears ringback tone.  (If answer
is required to enable call waiting, both get busy tone.)

> 5.  the called party has forward-on-busy to YOU and you have call waiting?

Intra-office: busy tone.  Interoffice: ringback tone interrupted by
call waiting alert.  Flash to answer and you can alternately hold
yourself (but can never talk to yourself because you can't cut through
a three-way connection :-).  (If answer is required to enable call
waiting, all the joy is gone and you just get busy tone.)  :-(


Lou Linneweh, Motorola Inc.