Date: Thu, 27 Jan 94 03:19:04 CST
From: varney@ihlpe.att.com
Subject: Re: Call Waiting/Three Way Together
Organization: AT&T

In article <telecom14.31.1@eecs.nwu.edu> izzy@access.netaxs.com (Michael 
Israeli) writes:

>> [TELECOM Digest Editor's Note: Try getting an actual three way call
>> installed between CW and 3WC (because flashing the hook could cause
>> one thing to hand you a CW at that point in time does your flash mean
>> you want to accept the new call or connect the other two. Since maybe
>> you do not want that to happen (the two you dialed to be joined
>> together) telco has chosen to block CW for that limited period of
>> time. Let us know.  PAT]

> Well, I attempted the following:

   [deleted excellent test of 3WC/CW interactions.] 

> So, I placed another call to Bell of PA.  I explained again my
> situation, receiving a CW tone during a three way call.  The agent
> looked into some book she had, and explained to me that I live in an
> area with a "5E" switching system, in which CW and 3WC can have NO
> interaction.  Whereas my friend who lives in a different area has a
> "1A" switching system, where they DO interact!

   Well, you probably don't want any excuses or a long history of the
pain involved in this area, so here's my nickel summary:

1) The interaction of 3WC and CW evolved over about 5 years in the
   early 1970s on 1E/1A ESS(tm) switches.  Trying to explain the actions
   of a switch to a customer who only has one input ("flash") at any
   given point lead to a really elaborate set of somewhat inconsistent
   modifications to the code, resulting in the current implementation.

   That implementation works basically as follows --

   a) Set up call, flash and place second leg of call.  From the moment
      of flash until the second call has answered, CW will return "busy"
      to any incoming call.  Flash will drop the second call leg.

   b) After second leg answers, without CW, a flash will drop the second
      call leg.  From the moment of CW alert (the "click" plus tones),
      a flash will connect to the CW caller, and leave the other two
      parties talking on your nickel.  Another flash (or disconnect by
      the CW caller) will connect you back to the 3W call.  If the CW
      caller does not disconnect, you can toggle back and forth between
      3W and CW calls as frequently as you desire.

   c) After second leg answers, and CW alert occurs, but you ignore it,
      and the CW caller abandons the call, there is no 3W call to reach
      with a flash.  But you don't know the caller has abandoned, so the
      CO "remembers" that you once had CW alert offered and treats a
      flash as an attempt to reach a CW call anyway (you get reorder,
      I believe).  This failed attempt erases the CW alert "memory",
      so that future flashes will drop the second leg of the 3W call.

   d) A side-effect of the "toggle back and forth" of 3W and CW is
      that, until the CW caller drops off your line, you cannot "drop"
      the second leg of the 3W call!
      
   Try writing that down, along with other interactions.  Better yet,
   try making that a general requirement for all switches, and extend
   it to other feature interactions, multi-line groups, etc.  It's a
   tough job.  That's why

2) Bellcore, in writing generic requirements for switches in the LSSGR,
   specified a simpler, more easily understood behavior:

   a) Set-up two legs of 3W call as before.  From the point of flashing
      to set up the second leg UNTIL you flash to drop the second leg,
      you cannot receive a CW alert -- and callers get a "busy" signal.

   b) If you drop the second leg, you can now receive CW alert and flash
      will connect you to the new caller.  But until the CW caller drops
      off of your line, you cannot initiate a 3W call (second leg) --
      each flash just toggles you from one call to the other.

   Much easier to explain to customers, and new switch vendors, than the
   1E/1A ESS implementation.  That's why the 5ESS(reg. tm) switch acts
   in this simpler manner -- it's what the TELCO (via Bellcore) specified.

  {The dime summary would have been half as long :) }

> It is a pain that my line is busy during 3WC, because I ordered CW for
> the specific reason of NOT loosing calls!  Are there any specific
> questions I should ask the phone company, or just give up on this one?

   CW does not alert 100% of the time -- for example, when you pick up
the phone and start dialing, CW alerting is blocked.  In fact, it will
be blocked until your called party answers.  Several folks have
complained that their CW is "broken" because 1) they receive normal
dial tone at the beginning of a call (implying there are no messages),
2) they dial a call and talk for awhile without any CW tones, 3) they
go on-hook and then off-hook, only to receive a "messages waiting"
interrupted dial tone.  Conclusion: CW isn't working!!  Fact: They
received a call sometime after the first dial tone and before the call
was answered, and their incoming call was routed to Voice Mail
immediately (no CW).

   But you do have several options:

A) Get a good voice mail system that will get any call where you can't
   receive the Call Waiting alert.  Sometimes CW won't be available with
   voice mail, and sometimes it will.  Either way, callers won't get
   "busy" during windows when CW is never available, such as during dialing
   and before answer on any call.  If you spend 20 seconds dialing and
   listening to ringing and only 2 minutes on a call, then callers have
   a 17% chance of getting busy even without the 3WC problem.

B) Ask if a Centrex-like package is available for residential lines.
   Some TELCOs have these priced in a bundle with Call Hold.  Better,
   if you can, just get the "Call Hold" feature added to your existing
   features.  Call Hold will not interpret "flash" as anything, but
   will give you dial tone -- from which you can dial a code to "hold"
   the current call and answer a CW caller or another code to "drop"
   the second leg of a 3W call.  Since you are using explicit codes, the
   Bellcore restriction of 3WC/CW does not apply, and you can get CW
   while on a 3W call.  (CW will still not work during the time you
   are dialing and waiting for a call to be answered.)

C) Get a second line, with hunting from the first on busy.  Avoids the
   CW blockage during dialing/unanswered-call periods, and you can drop
   the CW feature.  Or retain it and be able to be on 4 calls at once!

D) (The one I use.)  Get ISDN.  Even with 1 CSV B-channel, ISDN can
   support 3W calls explicitly (push the CONFerence button) and also
   support alerting of another incoming call (push the new call appearance
   to answer).  You can drop the new incoming call with another button.
   You can even MERGE the incoming call with your current outgoing call.

I'm sure I missed some other ideas ...


Al Varney -- just my opinion