Voice over Internet Protocol, also called VoIP, IP Telephony, Internet Telephony, Broadband telephony, Broadband Phone and Voice over Broadband  (continued)

Voice over Internet Protocol, also called VoIP, IP Telephony, Internet Telephony, Broadband telephony, Broadband Phone and Voice over Broadband is the routing of voice conversations over the Internet or through any other IP-based network.

Companies providing VoIP service are commonly referred to as providers, and protocols which are used to carry voice signals over the IP network are commonly referred to as Voice over IP or VoIP protocols. They may be viewed as commercial realizations of the experimental Network Voice Protocol (1973) invented for the ARPANET providers. Some cost savings are due to utilizing a single network - see attached image - to carry voice and data, especially where users have existing underutilized network capacity that can carry VoIP at no additional cost. VoIP to VoIP phone calls are sometimes free, while VoIP to public switched telephone networks, PSTN, may have a cost that's borne by the VoIP user.

There are two types of PSTN to VoIP services: DID (Direct Inward Dialing) and access numbers. DID will connect the caller directly to the VoIP user while access numbers require the caller to input the extension number of the VoIP user. Access numbers are usually charged as a local call to the caller and free to the VoIP user while DID usually has a monthly fee. There are also DIDs that are free to the VoIP user but chargeable to the caller.

VoIP Functionality

VoIP can facilitate tasks that may be more difficult to achieve using traditional networks:

• Incoming phone calls can be automatically routed to your VoIP phone, regardless of where you are connected to the network. Take your VoIP phone with you on a trip, and wherever you connect to the Internet, you can receive incoming calls.
• Free phone numbers for use with VoIP are available in the USA, UK and other countries from organizations such as VoIP User.
• Call center agents using VoIP phones can work from anywhere with a sufficiently fast and stable Internet connection.
• Many VoIP packages include PSTN features that most Telco's (telecommunication companies) normally charge extra for, or may be unavailable from your local Telco, such as 3-way calling, call forwarding, automatic redial, and caller ID.

VoIP allows users to travel anywhere in the world and still make and receive phone calls:

• Subscribers of phone-line replacement services can make and receive local phone calls regardless of their location. For example, if a user has a New York City phone number and is traveling in Europe and someone calls the phone number, it will ring in Europe. Conversely, if a call is made from Europe to New York City, it will be treated as a local call. Of course, there must be a connection to the Internet e.g. WiFi to make all of this possible.
• Users of Instant Messenger based VoIP services can also travel anywhere in the world and make and receive phone calls.
• Specialized mobile VoIP services enable users to talk over internet protocol and use VoIP based Instant Messenger services from their mobile phones.
• VoIP phones can integrate with other services available over the Internet, including video conversation, message or data file exchange in parallel with the conversation, audio conferencing, managing address books and passing information about whether others (e.g. friends or colleagues) are available online to interested parties.

Difficulty with sending VoIP faxes

One drawback is the difficulty in sending faxes due to software and networking constraints in most of the home systems. An effort is underway to remedy this by defining an alternate IP-based solution for delivering Fax-over-IP, namely the T.38 protocol. Another possible solution to overcome the drawback is to treat the fax system as a message switching system which does not need real time data transmission - such as sending a fax as an email attachment (see iFax) or remote printout (see Internet Printing Protocol). The end system can completely buffer the incoming fax data before displaying or printing the fax image.

Another drawback of VoIP service is its reliance upon another separate service - an Internet connection. The quality and overall reliability of the phone connection is entirely reliant upon the quality, reliability, and speed of the Internet connection which it is using. Shortcomings with Internet connections and Internet Service Providers (ISPs) can affect VoIP calls. Higher overall network latencies can lead to significantly reduced call quality and cause certain problems such as echoing. Certain providers, such as Time Warner Cable, offer a Voice over IP product to their customers without requiring an Internet service.

VoIP is not entirely reliant upon internet connections, however. VoIP systems can also utilize regular telephone lines and business-grade connections like T1 for voice service. A few business VoIP providers offer dedicated point-to-point T1 connections, not relying on an Internet connection for service. Although residential VoIP service typically uses only an Internet connection, business-grade VoIP service can use a variety of connection methods to provide ongoing phone service.

Many VoIP users still maintain a traditional analog voice line (business line) which allows them to dial emergency numbers and utilize a traditional fax machine.

Another drawback of VoIP is the likely inability to make phone calls during a power outage, though this problem is shared with some conventional phones which require more power than the landline itself can supply. Cordless phone units in particular are more affected by power outages as many do not have a battery backup option for the base station. This can be remedied with a battery backup like an Uninterruptible Power Supply. During a power outage one also has the choice to forward calls to a cell phone or alternate number.

If VoIP is used in solitary LAN (with no Internet connection), it would consume more resources compared to a PABX.

Modems are now available with lithium ion battery backup so the service can be used with no external power.

Because UDP does not provide a mechanism to ensure that data packets are delivered in sequential order, or provide Quality of Service guarantees, VoIP implementations face problems dealing with latency and jitter. This is especially true when satellite circuits are involved, due to long round trip propagation delay (400 milliseconds to 600 milliseconds for geostationary satellite). The receiving node must restructure IP packets that may be out of order, delayed or missing, while ensuring that the audio stream maintains a proper time consistency. This functionality is usually accomplished by means of a jitter buffer.

Another challenge is routing VoIP traffic through firewalls and address translators. Private Session Border Controllers are used along with firewalls to enable VoIP calls to and from a protected enterprise network. Skype uses a proprietary protocol to route calls through other Skype peers on the network, allowing it to traverse symmetric NATs and firewalls. Other methods to traverse firewalls involve using protocols such as STUN or ICE.

VoIP challenges:

• Delay/Network Latency
• Packet loss
• Jitter
• Echo
• Security

Fixed delays cannot be controlled but some delays can be minimized by marking voice packets as being delay-sensitive (see, for example, Diffserv).

The principal cause of packet loss is congestion, which can be controlled by congestion management and avoidance. Carrier VoIP networks avoid congestion by means of traffic engineering.

Variation in delay is called jitter. The effects of jitter can be mitigated by storing voice packets in a buffer (called a play-out buffer) upon arrival, before playing them out. This avoids a condition known as buffer underrun, in which the playout process runs out of voice data to play because the next voice packet has not yet arrived, but increases delay by the length of the buffer.

Common causes of echo include impedance mismatches in analog circuitry, and acoustic coupling of the transmit and receive signal at the receiving end.

Conventional phones are connected directly to telephone company phone lines, which in the event of a power failure are kept functioning by back-up generators or batteries located at the telephone exchange. However, household VoIP hardware uses broadband modems and other equipment powered by household electricity, which may be subject to outages dictating the use of an uninterruptible power supply or generator to ensure availability during power outages. Early adopters of VoIP may also be users of other phone equipment, such as PBX and cordless phone bases, that rely on power not provided by the telephone company. Even with local power still available, the broadband carrier itself may experience outages as well. While the PSTN has been matured over decades and is typically extremely reliable, most broadband networks are less than 10 years old, and even the best are still subject to intermittent outages. Furthermore, consumer network technologies such as cable and DSL often are not subject to the same restoration service levels as the PSTN or business technologies such as T-1 connection.