Telecom For Dummies

Like any other type of phone call, VoIP calls can experience problems, but the two concerns that are more prevalent within VoIP are linked to the very structure of VoIP. A plain-vanilla TDM (non-VoIP) call transmits sound on a circuit, with continuous, unimpeded information being sent in both directions. A VoIP call, however, transmits sound in small packets over an IP network that also has millions of other packets within it that are traveling in every direction.

The very idea of a transmission network filled with VoIP packets that come and go, finally arriving at the far end without losing any information, and in the correct sequence, seems like an achievement. But this is exactly what is expected of VoIP transmissions. As long as your LAN, your carrier’s network, and the Internet aren’t congested, everything should work fine. If any of these three elements do have congestion, your transmissions could arrive late, out of sequence and minus a few packets. The following sections go into what to do.

Getting beyond latency

Latency is a delay in the transmission of your data. Even though voice data is converted into digital packets, in order to be understood, it must come out the other end as a continuous transmission of sound. If a second of the conversation drops because it arrived late or was lost along the way, your call quality will quickly erode to static or sections of speech will be eliminated (a call treatment called clipping).

Latency can be caused in the coding and decoding process of your RTP stream, as well as the slowing down of a packet because of the geographic distance it is being sent. Latency issues are generally intermittent and can be caused by a variety of issues. In fact, a consistent latency problem is uncommon; if you are so lucky, you can adjust your hardware to accommodate it.

Dealing with jitter

Jitter refers to the fluctuations in latency. VoIP packets may experience a 10 millisecond (ms) delay during off-peak times, but during peak traffic hours for your carrier, your Internet provider, or your LAN, the delay may raise up to 60 ms. Jitter could cause portions of your call to disappear. If you hear short, split-second pulses of dead air in your conversations, these gaps are places where packets of data were supposed to be.

This problem is even more noticeable if your VoIP service is integrated on your LAN that also carries data, video, and Internet traffic. Your transmissions may sound great at times, but when your co-worker decides to download War and Peace, and your boss is videoconferencing with your New York office, you will probably see an instant jump in latency.

If your network tries to accommodate for this fluctuation, it has to readjust when the last page of War and Peace finishes downloading, and then again when your boss’s videoconference ends.

A jitter buffer is a function within your VoIP server that collects data packets, prioritizes them, and sends them out in sequence. They can help reduce jitter in VoIP transmissions, but excessive congestion will overload the buffer and result in lost packets.

 Tip  If you’re integrating VoIP into your existing LAN, hire an experienced professional to validate your design. The assignment of one piece of hardware in the wrong place will cause you prolonged pain and suffering.

Moving your existing telephone number to VoIP

Local number portability is the government-sanctioned freedom you have to move your phone number from one local exchange provider (like Bell South, Verizon, or Qwest, for example) to another. In order to use VoIP on your old phone number, your new VoIP carrier must have ownership of it. All carriers in the U.S. hand off their calls to the local carrier that owns the dialed phone number. This means that until your VoIP carrier is in charge of your number, you won’t receive any inbound calls on VoIP.

 Warning!  The process to migrate, or port your phone number from one carrier to another can be tedious, time consuming, and supremely frustrating. The requirement to handle the acquisition and release of local numbers is brand new for most carriers, so they’re still building their processes and procedures.

The migration of a normal, noncellular phone number may take anywhere from 5 to 50 days, depending on the carriers you are porting to and from. If you are beginning to port your phone number to a VoIP provider, keep an open mind, a positive attitude, and follow up every week to see how it is going.

 Remember  The current trend in the industry is to charge for the migration of telephone numbers. Don’t be shocked if your carrier charges $20 or more per phone number for a migration. The evolving migration process can include many delays that must be resolved. Issue resolution requires manpower, and manpower increases overhead. That means you have to pay more. As VoIP develops, expect more fees and charges to crop up as carriers respond to the market and protect their profitability.