North American Network Operators Group
Date Prev | Date Next | Date Index | Thread Index | Author Index | Historical

Re: IP telephony

  • From: Iljitsch van Beijnum
  • Date: Wed Sep 17 06:31:04 2003

On dinsdag, sep 16, 2003, at 23:38 Europe/Amsterdam, Christopher Bird wrote:

There has been much buzz of late about using IP telephony solutions in
place of the more common analog based solutions.



Traditional telephony has very high reliability (many years without
loss

of dial tone for some companies). From what I have seen in this group

about networking, router behaviors, etc. it seems to me that the IP

networks that exist aren't yet ready for the prime time of IP
telephony.

As we move buildings, my company is looking at installing an IP

telephony based solution (packet switched) instead of a traditional

analog based solution (circuit switched). I am worried that the

reliability will likely be lower than I am used to.



First of all, I don't use IP telephony myself (yet) so the usual
disclaimers and more apply.



The telephony world may claim very high reliability, but they don't
deliver when you need it the most. During 9/11 the phone network had
huge problems. Not so much because lines and equipment were destroyed,
but simply because too many people picked up the phone at the same
time. The same thing happened at a smaller scale during last months
blackouts.



The individual parts in an IP network are probably less reliable than
the individual parts in a POTS network, so you're likely to see more
outages. On the other hand, IP networks use a distributed model, while
POTS networks use a centralized model. So when something fails in an IP
network the consequences are usually not too serious (given good
network design of course) while with POTS you're usually in trouble.



Note that you need to make the distinction between IP-only calls and
calls that originate or terminate in the public POTS network. For the
former, you should be able to reach reliability levels that are no
worse than that of good PABX equipment, as long as you don't use the
public internet as part of your IP path. For the latter, you're not
going to improve upon a PABX. You may be able to achieve good
reliability for outgoing calls by building in huge amounts of
(geographic) redundancy in the POTS gateways, but I don't think this is
possible for incoming calls.



If you want to make calls over the public internet you're not going to
be very reliable. However, you can avoid 90% of the trouble by making
sure your calls go over the network of a single service provider (by
connecting all your offices to that ISP) as most of the trouble that
isn't simple outages (get more lines to protect against taht) has to do
with the interconnects between networks in one way or another. Of
course this ISP has to be a reliable one.