Inbound and outbound call center using PBX
I've used an inbound and outbound call center using PBX. Can anyone answer this question:
"Everything else being equal, what is the time difference between Analog
PBX and Primary Rate ISDN Service for disconnecting a call when an answering
machine, disconnected number, or busy signal is detected?"
An ISDN connection will normally detect a disconnected number or busy
condition almost instantly, and signal this to the caller in the D-channel.
An analog connection will normally play a tone to the user, which is harder
for a call center to detect reliably and takes a few seconds.
Detecting an answering machine is more difficult and there's no real
difference between analogue and ISDN PBXs there.
Consider that the call set up messages in ISDN are sent ahead of the
call, and a B channel is not actually used if the call cannot be completed
(more on why this is important later). That is, if the called party is "busy"
or "out of service" you will get the message stating this as soon as you launch
the call. If the called party answers, either live or by machine, you will get
an answer supervision message. Actual times that I have measured for this message
to arrive range from 100 ms to 320 ms This is enough time for you to switch the
call to an agent before the first hello. Voice recognition equipment can be used
to filter the machines out.
Now, why is it important that the B channel is not used for call set up.
In telemarketing you need to oversubscribe the number of circuits to support the
large number of calls the predictive dialer will need to make. In one project
I worked on with 100 agents they used over 300 lines, or a factor of 3:1. This was
approximately 11 T1's. When we converted the dialer over to use ISDN signaling we
were able to use trunk factor of 1.25:1. Which came to 5 Primary Rate Interface
trunks (PRI/T1). What was even more amazing was that the software that controlled
the system was able to actually send a "cancel call" message to the PBX to cancel
calls in progress when the algorithm determined that there would be no available
agent to take the calls in progress should someone answer. This saved a good deal
of money in calls completed and abandoned, not to mention not pissing off the consumer
any more than necessary.