What Is a VoIP Gateway?

VoIP technology is fast becoming the new standard for communications. Although there are still a number of people using the standard analog signal over copper wiring, there are many people venturing into VoIP with the hopes of cutting costs on their phone bill.

This is because VoIP technology converts the analog signal to data packets that are sent over a broadband network in the same way that data is sent. This bypasses the PSTN which bases its cost on the distance between where the call originated to its destination. Data does not have these restrictions and in most cases the data packets are sent on different routes and reassembled on the receiving end. Since many data packets from many data transmissions can occupy the same trunk at the same time, the cost of using the trunk is spread out over many users. With standard analog phone conversations, the line is limited to one call and is not available to any other calls until the conversation ends, so the person initiating the call is shouldering the entire cost.

Using true VoIP is when the caller initiates a call and the destination number is also using VoIP so that the entire call is transmitted over the data network in the form of data packets. But what happens if you were to call someone still using a standard analog phone? This is where a VoIP gateway comes into play. A VoIP gateway essentially acts as a translator between the old PSTN network and newer VoIP technology.

If a call comes into the gateway and is in the form of voice data packets, the gateway will decompress the conversation and convert the voice signal to digital and then to analog to be sent over the PSTN. If the call comes into the gateway as an analog signal, it is then converted to digital and then compressed using a codec to break up the conversation into packets to be sent over the data network. The gateway in simplest terms is nothing more than a media converter that transitions the call to whichever format is needed to be understood on the receiving end. As more and more people convert to VoIP technology, there will be less need for this conversion process to take place.

The codec used is dependent on the audio quality desired and the amount of bandwidth for voice data transmission available on the network. There are several, however the most common are G.711 and G.729. The G.711 usually provides a better audio quality but also requires a much larger amount of bandwidth to support. The G.729 is probably the most popular because it provides the best compromise in regards to audio quality with minimal bandwidth requirements. The G.711 takes 64 Kbps versus only 8 Kbps for the G.729. Most VoIP gateways support both codec's.

There are also various VoIP protocols supported by most gateways with the most common being the H.323 and SIP protocols. However, H.323 is on the way out as the newer and more flexible SIP takes its place. SIP or session initiation protocol is a text-based protocol that controls the initiation and break down of a VoIP session. It allows for multiple technologies to be present in one session and is making the convergence of different multimedia such as video, voice and instant messaging possible.

In most cases, the gateway is used in one of two ways to allow intercommunication between VoIP and non-VoIP hardware. One way is to use a gateway to convert incoming calls from the PSTN to VoIP calls so that they can be received on a VoIP system. Another way is to connect a standard phone system to the network so that calls can be made via VoIP. In both scenarios, they are generally setup using the protocols and codecs described above.

Gateways can come in either software or hardware form. Hardware based gateways are more popular and can either be a standalone box or could be a card or module added on to existing equipment. Software versions are set up on a server where existing servers can be leveraged to run the gateway software in addition to other services. As a general rule, the software solution is a bit cheaper than its hardware counterparts.

The gateway is only part of the equation and performance is based on many factors such as available network bandwidth, security, protocols and codecs. All of these different aspects of VoIP configuration are going to play a role in the quality and reliability that one could expect. Since most VoIP calls today still interact with the PSTN, a VoIP gateway should be included in any VoIP communication solution. Before deciding on a hardware or software solution, determine if there are already resources available that can be leveraged to keep costs down. This way you can you still take advantage of VoIP while waiting on the rest of the world to catch up.