VoIP Over Voice-Grade Cable

When you see a Voice-over-IP (VoIP) phone system diagrammed out on paper, it looks great – either a hosted service or a self-hosted IPPBX (Internet Protocol Private Branch Exchange) connected to your data network with IP phones as end points. You may see a nice color drawing with a pretty blue line connecting each IP phone back to a network switch. It’s beautiful – on paper.

In real life,however, this is not how it always turns out. In the real world, that pretty blue line can be problematic. In the real world, existing phones run on voice grade cable and there may not be data grade cable in all the locations where an IP phone is needed. In the real world, voice grade cable services phones far beyond the 100m limitation of data cables. In the real world, there may not be AC power near the location of one of these problem phones and, in order to provision an IP phone, power and Ethernet need to be delivered over the existing voice cable. In the real world, customers may not have the budget to revamp their cable infrastructure to support VoIP phones.

For those of us living in the real world, there are three primary options for deploying VoIP in these challenging environments. The first and most obvious is to re-cable those problem locations, making them comply uniformly to the rest of your data cabling. While this may be the best, lowest cost option, there are many situations where this is not practical. Our company is located in New Mexico and some of our customers are located in historic adobe buildings in Santa Fe, or other old buildings that simply cannot accommodate  cable additions. We have a customer with a 5-story walk-up in New York City. Running cable in that building could be extremely expensive and could involve code issues, inspections, etc.

The second option is to use wireless (as in Wi-Fi). Wireless can be a good solution in the right situations. There are many considerations to making wireless work for VoIP, like voice security, Quality of Service and voice traffic prioritization, seamless roaming, coverage holes etc. I plan to write a post about wireless VoIP soon, so watch for more on this subject later.

But there is a third option – that of using other innovative solutions like the Phybridge UniPhyer and Adtran ActivReach. These are essentially data switches that can deliver Ethernet and power over a single pair of telephony-grade wire (24-26 AWG UTP). These solutions are designed to allow customers to transform their existing voice infrastructure into an IP path with power ideal for IP Telephony deployment. These devices use a technology called Long Reach Ethernet or LRE. LRE is similar to DSL and can run over voice-grade cable for long distances into the thousands of feet. By adding power to the cable pair as well, these vendors have developed a product they call PoLRE, for Power Over Long Reach Ethernet. There are some limitations to PoLRE, which I will discuss, but in the right situation, this can be the best, lowest cost alternative.

One of the advantages of the LRE switch approach is that it is simple and low-risk. Both of the previous options could have hidden costs and could take significant time to deploy. With LRE, you simply install the LRE switch, connect it to your existing voice cable and you are done. This could be an interim solution, say if you decide to delay re-cabling your building until a later date. It could also be a permanent solution.

LRE has some limitations. Often, in a VoIP scenario, you will see PCs plugged into the phone. IP Phones have an internal Ethernet switch, allowing you to essentially “daisy chain” the PC and the phone together. The catch is that the uplink from the phone to the data switch has to have sufficient bandwidth to support both devices. Another way to say that is that both devices will share the available bandwidth on that uplink cable.

In the LRE case, bandwidth can be limited on the uplink, to the point where it is not feasible to run the PC on the same link. In this case, you have what is called a Parallel Voice Network (PVN). This may work, depending on your situation, especially if your PCs are already running wireless.

Are cable issues keeping you from migrating to VoIP? Does PoLRE make sense for you? Share your thoughts in the comments.