What to look for

The features of VoIP may just be enough to persuade you one way or the other.

Look for the following:

• A real phone number , so that anybody can call you, not just other VoIP users. In VoIP terminology, this is known as direct inward dialing, or DID.
• Multiple phone numbers for a single VoIP phone lets family members have their own personal number.
• The ability to call regular phone numbers at a reasonable or low price, particularly for local calls.
• Quality of Service (QoS) technology so that your voice traffic is given priority over data traffic as it traverses the internet. This is especially important if you continue to undertake other internet activities while you chat using VoIP.
• Session Initiation Protocol (SIP) technology is a method of managing VoIP calls. It identifies the recipient of your call, even if they change location, and ensures both parties in a VoIP call use the same set of features. It’s a simple matter to add somebody to a conference call or to put them on hold using SIP. Older technologies lack these features.
• Encryption is important because your calls may be routed through the public internet.

How it works Telephone calls connect you and the recipient using a dedicated line. The connection stays open until you close it (see diagram, right). This is known as ’circuit switching’. Computer data travels quite differently. Fragments of the message, known as packets, travel via many different routes to reach their destination — there’s no continuous connection between the two end points (see diagram, below right). The advantage to sending voice traffic as packets is that it’s much cheaper. If you’re calling somebody who also has VoIP, it’s free — or at least bundled into the regular cost of your ISP account. The disadvantage is that packets may not arrive in sequential order, so sound quality can be affected. Although the principle is simple, getting VoIP to work is more complex. In practice, a broadband connection with 128 kilobits per second (kbps) for both download and upload will produce efficient VoIP with good quality sound.