H folks,
We are going to replace our existing digital PBX phone system (which has
its own CAT3 wiring). I am desperately seeking objective information on the
issues from people who aren't trying to sell me something. If any of you
have expertise on this topic, perhaps you could answer some questions.
My knowledge of telephony is virtually nonexistent, and my knowledge of
networking is limited.
The current PBX system manages about 150 extensions. We would like to go to
at least 200 initially, and perhaps as many as 300-350 later.
Existing phone and internet service are both currently provided by Level 3
(formerly TWTelecom). We have fiber coming into the building that carries
both phone and internet service. Somehow, using Adtran and PRI devices, the
bandwidth ascribed to phone vs internet is dynamically managed in response
to demand. However, the internet connection is maximum 25 Mbps down and 5
Mbps up. The system delivers 12 phone "lines". We also have a fax server
with a Brooktrout fax card that handles 20 incoming DID numbers and two
outgoing (I think "analog") lines, and it has its own Adtran device.
The computer data network has 4 48-port gigabit switches. They are NOT POE.
Phone vendors want to sell us a VoIP internal phone system using POE
switches and our current network CAT5 cabling.
My biggest concern is network throughput and avoiding internal network
congestion.
The phone sales people have trouble understanding this concern. They don't
seem to be able to distinguish between congestion resulting from use of the
INTERnet as opposed to INTRAnet.
My network doesn't suffer from network printing, but it is pretty busy. I
am trying to get a straight answer on exactly how much of my internal
network bandwidth a very busy VoIP phone system (at times all 12 "lines"
are in use) will suck up. There are all kinds of advantages to a VoIP
system, I know, but if it slows down the data traffic on the network I am
going to be an unhappy camper.
I understand that for VoIP to be usable, its packets have to get priority
over other data traveling across the network (otherwise the voices "break
up"). This is what concerns me about the technology. If there are 12 (or
more; growth is inevitable) VoIP conversations taking place at once across
my network, what's going to happen to the responsiveness of the constant
file server access, accounting database access, and internet access (for
the fat-client payroll system and Medicaid billing system) that is also
going on across the network?
Are there options to add more bandwidth to the network? Affordable options?
For example, are there faster-than-gigabit switches that can use the
existing CAT5 (not 6) cabling? And would it matter, since the computers
only have gigabit network chips?
Secondarily, if we dispense with the Level 3 Adtran/PRI stuff and go to SIP
networks, am I going to need a lot more INTERnet bandwidth to make that a
reasonable option?
Any help on this--again, from objective sources not trying to sell me
anything--would be very much appreciated.
Thanks in advance.
Ken Dibble
www.stic-cil.org
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