Merging voice over data is not new to the telephone industry. The most common application over the last 10 years has been to use a voice/data mux to split channels on a T-1. A T-1 is a high speed digital circuit with 24 channels which can support 24 phone calls. A voice/data mux can strip off a certain number of dedicated channels for data (in 56 or 64K increments) and give the rest of the dedicated channels to the phone system. This has worked very well to save end users on their phone bills and tie branch offices with main offices so that multiple phone systems work like one large system. Other advantages have been centralized voice mail and centralized call accounting. Having a single voice mail system gives you the ability to forward messages to other mail boxes etc.

Voice Over IP places phone calls over your LAN or WAN by mixing in the data bits on a single data circuit. This presents a number of techical problems which should not be ignored. First of all, data flowing with IP protocol is going down the data circuit in packets. These tend to burst at various speeds as traffic permits. In the above example, dedicated data circuits flow at constant speeds. Voice traffic needs to flow at a steady speed so that conversations sound normal. This requires some form of QOS (Quality of Service) in the router to assure that voice packets get priority.  Voice packets can be compressed so that they take up much less than the 56K that we have used in dedicated T-1 circuits. Compression down to 16K seems to provide a quality voice sound, typically called "toll quality". The major advantage to VOIP is that once a phone call hangs up, the bandwidth in use is available for data, so the data speed goes back up. Another minor issues is that the gathering and merging of these packets does take some time, so there is typically some delay in the phone call. Most users will not notice it or complain, however.

The next issue is how far to go to merge the voice and data. Many manufacturers have come out with "pure" IP based phones and phone systems. They want end users to have an IP phone on their desk which shares the same Ethernet outlet as their PC.  Below is a list of technical concerns using VOIP.

1. 300' limitation on Ethernet wiring affects warehouse locations.

2. Additional switch ports needed for phone locations where there isn't a PC.  Typically, more expensive switches with POE (Power Over Ethernet) to provide electricity for IP phones.

3. CAT V or Ve wiring usually suggested or required.

4. Service issues:

a. When there's a problem, the time to isolate the problem could be hours as finger pointing occurs.
b. Switches are typically very reliable, but servers run on software etc.
c. The computer industry service people typically don't want to come out past 5pm.
d.  Some manufacturers provide service next day from the nearest major city.  That means down time when a failure occurs.

5. Investment protection: Traditional PBX systems last 10 years and longer. Computer systems get obsolete in 4-6 years.

6. Power outages. Most PBX systems are DC operated and are connected with battery backup to stay up for 2+ hours in the event of a power outage. Computer networks run on 110 volts and require expensive UPS systems for every switch and server to stay up for 15-30 minutes.

7. E-911. Illinois and a few other states require that a phone call to E-911 send the true caller ID of the phone making the call. In Illinois, buildings with less than 40,000 sq. ft. are exempt, but others need to comply. An IP phone, like a PC, can be plugged into any port on the LAN, so while it's easy to move phones, keeping track of their ID may be a challenge.

8. Cost. IP phones currently cost more than traditional digital speaker phones.  

9. Lightning protection. Most LAN's aren't protected against lightning damage. Phone system manufacturers have experienced lightning for many years and have protection built into the systems. When you connect phone lines (different ground) to a system that is also connected to an electrical ground, you have an open invitation for mother nature.

10. Data traffic issues. Can your LAN support data traffic and voice traffic at the same time without affecting either?

11. Hackers and viruses. It's bad enough to know that your PC's and servers are vulnerable. Keeping your phone system separate avoids disasters.

12. IP phones require power. That means desk top AC adapters for each phone, or run DC power on your LAN wiring for a switch that's powered or a patch panel with DC power. Don't forget to include these items in your cost comparison.

13. If you plan to run your phones over your IP network IN the building, make sure you have switches instead of hubs.

In summary, we believe the safest, reliable thing to do with VOIP is to merge your inter-building voice traffic to an IP network as the call leaves the building. The potential minimal cost savings by merging the two provides "free" calls to branch offices. Long distance rates have come down in recent years and most users don't save enough money over the years to justify adding any circuits to save money on phone calls.  Phone systems have IP trunk ports so that calls going to a branch office can be dialed with a 3 or 4 digit number so you can dial straight to the desk instead of reaching an attendant or an automated attendant.

Steve Autor is President of Digital Communications, Inc.