BackVoice over IP

Introduction to Voice over IP

Voice over IP has traditionally been restricted to larger corporations for their own internal use. Smaller companies and home users have been put off VoIP due to the daunting task of installing new technology where there was very little user-friendly information about and also because of the high costs involved. Voice over IP devices have come down in price dramatically recently and they are no longer aimed at just the niche market.

Voip Phones

VoIP Phones connect directly to your LAN via an RJ45 Ethernet connection and provide quick and easy access to Internet based telephony. Typical options include a PSTN port for use with your ordinary phone line, answering machines, call forwarding and more.

Gateways

A VoIP Gateway is a device which connects a telephone device or line to a computer network. On the computer connection side, devices may just have an Ethernet connection or they may incorporate a cable-modem or ADSL modem. At the telephone side, products usually provide standard analogue (also called PSTN or POTS) connections.

The Channel

In principle you can use a VoIP gateway to communicate with anyone else on the Internet who is similarly equipped, or has software to drive their PC/Soundcard. For best performance it is preferred that both ends have some form of broadband connectivity.

A more common use is to connect two or more sites for free calls between the sites. There may already be a data-link between the sites or the prospect of free-calls may be the spur to set this up. Each telephone conversation requires a channel of less than 10k, so any data-link from 64k up would be reasonable as long as it is fairly stable, has minimal delay and is not already congested. Suitable choices for the channel are • Direct wired/RF/IR/Microwave Ethernet connection • Leased Line • ISDN/ADSL/SDSL

The protocols and call-routing

The two principle protocols for using VoIP are MGCP and H.323. The principle difference between the two protocols for the beginner is that MGCP requires a call agent. This is a piece of software or hardware responsible for the routing of calls. A simple H.323 set-up can be configured with all routing information held within the voice gateway itself. In a very simple H.323 set-up a call can be placed between two phones, connected to gateways, by just dialling the IP address of the other gateway.

See VOIP Example Installation notes