kester@houxq.UUCP (09/22/83)
About one or two months ago, I posted an article requesting
information about Central Office Hunt Group Architecture.
This article is to repay those who had helped me. I can not
gurantee the accuracy of the following information.
There is really no limit to the number of local loops a
regular hunt group can support. There is probably a limit
of one thousand lines to start, but you can always call-
forward the last line to another one thousand line hunt
group. In this way, a hunt group of a size of 10,000 lines
can be constructed. However, a regular hunting size of more
than one hundred is not recommended. You can easily subject
your services to a killer trunk problem -- For example, if a
bad trunk is the number 2 loop in the hunting table, then
you will only have 1 loop available for all users.
Uniform Call Distribution service is probably the best
hunting service one would want. The service gurantee even
traffic load on all idle loops in a hunt group. The largest
size of such a service is said to be 1024 loops. This
number was quoted to me by Southern Bell folks at Atlanta
and a person who knows about NJ Bell. The service is
available with additional charges if you subscribe to ESSX
or CENTREX automatic call distribution services. It is
obviously a ESS service and is not available on a cross bar
switch. I have seen the UCD offered by C&P as a stand alone
service to National Institute of Health in Washinton D.C.
They have roughly 800 lines under one rotary.
Busy Out key does knock out a local loop. However, it is
not guranteed to work every time. The way each operating
company reponds to busy out varies. Usually a trouble card
is dropped whenever a busy out loop is detected.
Lead time to a large (hundreds of lines) hunt group can be
as much as 12 to 14 months depending on the site location,
the availability of local loops and the availability of
inter-central office trunk lines. The way telephone company
bring their local loops to your site is their business. They
are obligated to provide you the service under a pre-set
tariff. Of course you can negotiate a transmission
methodology that fits you best, but then you will have to
negotiate the cost with the phone company.
The problems of managing a large number of dial-in lines
usually include the following.
1. Finding out just which line is giving you trouble.
This requires some sort of real-time monitoring
capabilities.
2. After a trouble line has been located, one would like
to isolate the probleem to device level. That is to
find out wheter the local loop, the modem, or the
frontend port is giving you hell. You can then call
up the responsible maintenance personnel to fix the
bug.
3. Switching a subset of your modems to some other
frontend because of routine maintenance of your
frontends or because of a failure condition.
Obviously you will have to have extra frontend ports
available for this kind of operation.
The above functions can be fulfilled by some of the modern
electronic matrix switches available in the market. But
they do cost money.
Special thanks to Norm Thompson at ATT-BTL who has given me
a great deal of good information.
Kester Fong
ATT Information Systems Labs
!houxq!kester