VoIP, is a methodological group of technologies for delivery of voice communication or multimedia sessions over internet. There are other terms associated also to VoIP such as IP telephony, Internet telephony, broadband telephony, and broadband phone service. This technology has improved the way people communicate since it basically transmit voice over digital network. Although internet is not strictly necessary for VoIP, it uses the same protocols or set of rules used to allow orderly communication. Thus, voice over Internet protocol means voice that travels by way of the same protocols used on the Internet. Actually, the internet protocols support corporate, private, public, cable, and even wireless networks.
In other words, VoIP unify in a single converged communication network many organization’s locations. This includes mobile workers as well. After the network is already established, it provides an unparalleled range of telephony support services and features .
Nevertheless, digital network was not the easy tool we know today. The forerunner of VoIP was POTS (plain old telephone service). POTS was a telephone service that employed signal transmission over copper loops. It provided its services from telephone companies from 1876 to 1988, when Basic Rate Interface or BRI was introduced. POTS ran over a network called the PSTN, or public switched telephone network. These POTS telephone systems use the tried-and-true method of telephone service known as circuit-switched.
On his book “VoIP For Dummies” Timothy V.Kelly, the author, states that “ VoIP technology enables traditional telephony services to operate over computer networks using packet-switched protocols. Packet-switched VoIP puts voice signals into packets, similar to an electronic envelope. Along with the voice signals, the VoIP packet includes both the caller’s and the receiver’s network addresses. VoIP packets can traverse any VoIP-compatible network. Because VoIP uses packets, much more information can be carried over the network to support and enhance your communication needs when compared to traditional telephony methods.” This means, since VoIP is an alternative, it can can greatly reduce or eliminate POTS-related costs. Also, VoIP enhances productivity, leaving a bigger budget for things other than paying telephone bills.
VoIP network has a mathematical model that allows voice packet to pass through several nodes before arriving to the destination. This made possible that voice signals can travel the same packet-switched network infrastructure that companies already use for their computer data. In the POTS world, if a line is down, the call can’t go through. In a packet-switched network, multiple routes can be established, and packets can travel any of the available routes. If one of the lines supporting the network is down, the packet can switch to another working route to keep the call up.
Communication on the IP network is perceived as less reliable in contrast to the circuit-switched public telephone network because it does not provide a network-based mechanism to ensure that data packets are not lost, and are delivered in sequential order.Therefore, VoIP implementations may face problems with latency, packet loss, and jitter.
By default, network routers handle traffic on a first-come, first-served basis. Network routers on high volume traffic links may introduce latency that exceeds permissible thresholds for VoIP. Fixed delays cannot be controlled, as they are caused by the physical distance the packets travel; however, latency can be minimized by marking voice packets as being delay-sensitive with methods such as DiffServ.
Although it is possible to abort a less important packet in mid-transmission, this is not commonly done, especially on high-speed links where transmission times are short even for maximum-sized packets. VoIP endpoints usually have to wait for completion of transmission of previous packets before new data may be sent.An alternative to preemption on slower links, such as dialup and digital subscriber line (DSL), is to reduce the maximum transmission time by reducing the maximum transmission unit. But every packet must contain protocol headers, so this increases relative header overhead on every link traversed, not just the bottleneck (usually Internet access) link.
VoIP also makes possible other services that older telephony systems cannot provide because, VoIP telephony services work well over all kinds of networks and also work with any IP-enabled device such as an IP telephone, a computer, or even a personal digital assistant (PDA).
All IP phones have one important thing in common: a built-in network interface card (NIC), just like a computer uses. The NIC is critical for any network device because it provides the device with a standardized physical, or MAC, address and a way to communicate over the network. (MAC stands for media access control.)