IP telephony

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. However the cost
savings look quite compelling, so I am torn.

The more I read in here about threats and attacks against IP networks
and the amount of maintenance we need to have in place to keep our IP
networks hanging together, the more I am concerned about the viability
of an IP telephony solution.

Does anyone here have any thoughts, experiences, etc. about the use of
IP telephony in corporate environments?

Thanks in advance


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Christopher Bird wrote:

Does anyone here have any thoughts, experiences, etc. about the use of
IP telephony in corporate environments?

IP telephony works alright if you take the neccessary precautions for performance
management, monitoring, rate-limiting unwanted traffic, etc. which you should do
anyway. Most organisations have gotten along and are acting in reactive mode
whenever new "threats" are "discovered".

Most problems with IP telephony come from the "router people" not talking
to the "firewall people" and both of them not talking to the "telephone people".
If you can get those lines working, you�ll likely to succeed. If you don�t,
go with the traditional way, because then you don�t have to make the people


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.

Thank you Henry, Peter, Mehdi, Todd, Bob, Irwin, Tracy, John, Karsten,
Karl, Shawn. Howard, Darren, Mike and Paul for taking the time to
answer. This has helped greatly.