VoIP allows telephone calls to be made over computer networks. It alters analog voice signals into digital data packets and using the Internet Protocol (IP) supports real-time, two-way transmission of conversations.
VoIP calls can be made using a service provider and standard computer audio systems. Alternatively, many service providers support VoIP through telephones which use special adapters to connect to a home computer network. Many VoIP implementations are designed on the basis of the H.323 technology standard.
Although a very different technology and approach are used to provide voice services, some of the same components that are used in the Public Switched Telephone Network (PSTN) are also found in the VoIP environment.
VoIP provides support to networks which must perform all the same tasks that the PSTN does, in addition to performing data and signaling gateway functions to the existing public network. There are four major components found in any VoIP environment. These are:
- Media/signaling gateways
- The IP network
- Call processor/controllers
- Subscriber terminals
The IP Network
A network which supports VoIP technology can be viewed as one logical voice switch in distributed form with the IP backbone providing connectivity to the distributed elements in the network. This IP infrastructure must guarantee smooth transfer of voice and signaling packets to the VoIP elements.
Due to infrastructures dissimilarities IP networks must treat voice and data traffic differently because latency in voice transmission is more noticeable to the user than latency in data transmission. There are differences regarding correlations can be made to VoIP and circuit-switching components.
A circuit switched network can be classified as a Time Division Multiplexing (TDM) network, that allocates channels and reserves bandwidth as it is needed out of the trunk links interconnecting the switches. IP networks are dissimilar than circuit switching networks because they are based on a packet and built on statistical availability.
Quality of Service (QoS) defines a guaranteed output level and Class of Service (CoS) defines that packets of a certain application are given priority. This guaranteed outputs, and prioritizations are necessary for real-time applications to ensure that the voice service is unaffected by other traffic flows.
Call processor/controllers uses system software, which sets up and monitors calls, maintains the dial plan, authorizes users, performs phone number translations, coordinates some or all the call signaling, delivers basic telephony features, and may control the bandwidth utilization on each link.
Call processors or controllers house the signaling and control services which coordinate the media gateway functions. A call process/controller is called soft switch, call agent, call manager, or gatekeeper depending on its function in the VoIP supported network. The amount of functionality provided depends upon particular VoIP product used.
VoIP gateways are used for call origination, detection, analog-to-digital conversion of voice and creation of voice packets. In addition, media gateways offer features such as echo cancellation, voice compression, silence suppression and statistics gathering.
In several physical forms gateways exist including a physical board or blade found in a dedicated telecommunications frame or a common PC running VoIP software. Media and signaling gateways provide features and services that can span a wide spectrum. Their functions can be divided into three key gateway types:
★ Media Gateway (MG): This allows the delivery of media signals between the IP Network and circuit switched or traditional telephone network. This translates information is delivered on the IP network using packet formats to Pulse Code Modulation (PCM) encoded voice on the PSTN side and vice versa.
Media Gateway offers trunking functions which acts as interface between the telephone networks and a VoIP network.
★ Signaling Gateway (SG): This gateway provides direction to the signaling functions between the IP network and the switched circuit network. It may offer correlation between the H.323 signaling on the packet network side and the signaling system seven (SS7) signaling on the PSTN side.
★ Media Gateway Controllers (MGC): By providing the call setup and processing functions the media gateway controller communicates with both the MG and the SG. This gateway uses a dedicated protocol like Media Gateway Control Protocol (MGCP) for inter-gateway communication functions.
The user or subscriber's telephone instrument is the IP phone. This device offers real-time, bi-directional communication with another compatible device. The IP phone offers voice communications, and may offer other optional services such as data or video.
Because Internet Voice is digital, VoIP offers features and services that are not available with a traditional phone. You need not retain and pay the additional cost for a line just to make telephone calls if you have a broadband Internet connection. Using Internet Voice, you can talk to multiple people for as long as you like without any additional cost.