User`s guide

Voice over IP Frequently Asked Questions

The following section covers some of the frequently asked questions a data communications manager

or telecommunications manager may have as they begin to learn how a VOIP solution can solve their

telephony challenges and save them money.

Bandwidth Requirements

“How can I be assured that my data “pipe” will not be  ooded by voice traf c and negatively impact the

timely delivery of data services?”

One common misconception about VOIP is that it is a bandwidth hog. In reality, with the use of voice

compression, voice is a very ef cient type of traf c. A vocoder (voice encoder/decoder) provides multiple

voice compression standards which range from G.723 (5.3K bps/6.3K bps) to G.729 (8K bps) to G.711

(full, uncompressed 64K bps) and can be selected on a system or a per port basis. This allows the

administrator to minimize network bandwidth requirements or maximize voice quality on an of ce-

by-of ce or user-by-user basis. With MultiVOIP, the majority of applications are optimally con gured

for voice quality with minimal bandwidth requirements by simply using the factory defaults for voice

compression.

As a rule of thumb, 14K bps of bandwidth per call is ideal. This includes the compressed voice packet

and the IP overhead. To determine total VOIP bandwidth needed per location, take the number of VOIP

ports or channels being utilized and multiply by 14K (ideal bandwidth). Then double this number, to

accommodate for both voice and data traf c, to get the total bandwidth required for optimum voice

quality.

Company Example: Los Angeles branch of ce is using 2-ports

2 x 14K = 28K x 2 = 56K bps minimum bandwidth

Using the formula, the company needs a minimum bandwidth of 56K bps. Since their data network

already has a 128K connection, bandwidth will not be an issue (see diagram on p. 4).

It should also be noted that bandwidth is used only when someone is speaking. With MultiVOIP,

a silence suppression/Voice Activation Detection (VAD) feature is an option that frees unused call

bandwidth for data traf c. This is signi cant, since callers are usually silent for 60 percent of the call.

Voice Quality

“I’m not yet convinced that Voice over IP can deliver business quality voice.”

Independent tests of VOIP systems have shown that they are perfectly capable of delivering “toll-quality”

voice. Earlier implementations were criticized for excessive noise and other quality of service issues.

Today, better algorithms, quicker voice compression, and the availability of high-speed communication

links have all made VOIP implementations a viable technology.

The actual voice quality is affected by a number of factors: WAN bandwidth (the higher the better),

voice compression (as discussed previously) and network conditions including latency, jitter and packet

loss.