Voice over IP

Voice over Internet Protocol (also called VoIP, IP Telephony, Internet telephony, and Digital Phone) is the routing of voice conversations over the Internet or any other IP-based network. The voice data flows over a general-purpose packet-switched network, instead of traditional dedicated, circuit-switched voice transmission lines.

A typical analog telephone adapter for connecting an ordinary phone to a VoIP network

Protocols 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.

Voice over IP traffic may be deployed on any IP network, including ones lacking a connection to the rest of the Internet, for instance on a private building-wide LAN.

Advantages

Cost

In general, phone service via VoIP costs less than equivalent service from traditional sources, mainly due to selling below market costs. There are also some cost savings due to using a single network to carry voice and data. This is especially true when users have existing under-utilized network capacity that they can use for VoIP without any additional costs. One must note that the maximum upstream in your Internet connection is the final throttle and service is not as good as standard telco services. VoIP phone calls (even international) are widely regarded as free. While there is a cost for their Internet service, using VoIP over this service usually does not involve any extra charges, so the users view the calls as free. There are a number of services that have sprung up to facilitate this type of "free" VoIP call. Examples are Free World Dialup, Skype and TheGlobe .

Functionality

VoIP makes easy some things that are difficult to impossible with traditional phone networks:

Incoming phone calls can be automatically routed to your VoIP phone, irrespective of where you are connected to the network. Take your VoIP phone with you on a trip, and anywhere you connect it to the Internet, you can receive your incoming calls.
Call center agents using VoIP phones can work from anywhere with a sufficiently fast Internet connection.
VoIP phones can integrate with other services available over the Internet, including sending and receiving messages or data files in parallel with the voice conversation, audio conferencing, managing address books and passing information about whether others (e.g. friends or colleagues) are available online to interested parties.

Drawbacks

VoIP technology still has a few shortcomings that have led some to believe that it's not ready for widespread deployment. However, most industry analysts have predicted that 2005 is the Year of Inflection, which is the year in which more IP PBX ports will ship than legacy digital PBX ports.

Implementation challenges

Because IP does not provide any mechanism to ensure that data packets are delivered in sequential order, or provide any Quality of Service guarantees, VoIP implementations may face problems dealing with latency, especially if satellite circuits are involved. They are faced with the problem of restructuring streams of received IP packets, which can come in any order and have packets missing, to ensure that the ensuing audio stream maintains a proper time consistency.

Another main challenge is routing VoIP traffic to traverse certain firewalls and NAT. Intermediary devices called Session Border Controllers (SBC) are often used to achieve this, though some proprietary systems such as Skype traverse firewall and NAT without a SBC by using users' computers as super node servers to route other people's calls.

Keeping packet latency acceptable can also be a problem, simply due to transmission distances.

Reliability

Telephones 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. In order to use VoIP during a power outage, an uninterruptible power supply or a generator must be installed on the premises. It should be noted that many early adopters of VoIP are also users of other phone equipment such as PBX and cordless phone bases that also rely on power not provided by the telephone company.

Some broadband connections may have less than desirable reliability. Where IP packets are lost or delayed at any point in the network between VoIP users, there will be a momentary drop-out of voice. This is more noticeable in highly congested networks and/or where there is long distances and/or interworking between end points.

Emergency calls

The nature of IP makes it difficult to geographically locate network users. Emergency calls, therefore, can not easily be routed to a nearby call center, and are impossible on some VoIP systems. Moreover, in the event that the caller is unable to give an address, emergency services may be unable to locate them in any other way. Following the lead of mobile phone carriers, several VoIP carriers are already implementing a technical work-around. The United States government had set a deadline, requiring VoIP carriers to implement e911, however, the deadline is being appealed by several of leading VoIP companies.

This is a different situation with IPBX systems, where these corporate systems often have full e911 capabilities built into the system.

A simple solution to this problem is to store the local emergency numbers on speed dial which is usually even faster than having to be transfered by the 911 operator.

Integration into global telephone number system

Whilst the traditional Plain Old Telephone System (POTS) and mobile phone networks share a common global standard (E.164) which allocates and identifies any specific telephone line, there is no widely adopted similar standard for VoIP networks. Some allocate an E.164 number which can be used for VoIP as well as incoming/external calls. However, there are often different, incompatible schemes when calling between VoIP providers which use short codes that are provider specific.

Single point of calling

With commercial services such as Vonage, it is possible to connect the VoIP router into the existing central phone box in the house and have VoIP at every phone already connected. Other services, such as Skype & PeerMe require the use of a computer, so they are limited to single point of calling. Some services, such as BroadVoice provide the ability to connect WiFi SIP phones so that service can be extended throughout the premises, and off-site to any ___location with an open hotspot..

Mobile phones

Telcos and consumers have invested billions of dollars in mobile phone equipment. In developed countries, mobile phones have achieved nearly complete market penetration, and many people are giving up landlines and using mobiles exclusively. Given this situation, it is not entirely clear whether there would be a significant higher demand for VoIP among consumers until either a) public or community wireless networks have similar geographical coverage to cellular networks (thereby enabling mobile VoIP phones, so called WiFi phones) or b) VoIP is implemented over legacy 3G networks. However, "dual mode" handsets, which allow for the seamless handover between a cellular network and a WiFi network, are expected to help VoIP become more popular.

Adoption

Mass-market telephony

A major development starting in 2004 has been the introduction of mass-market VoIP services over broadband Internet access services, in which subscribers make and receive calls as they would over the PSTN. This requires an analog telephone adapter (ATA) to connect a telephone to the broadband Internet connection. Full phone service VoIP phone companies provide inbound and outbound calling with a DID. Many offer unlimited calling to the U.S., and sometimes to Canada or to selected countries in Europe or Asia, for a flat monthly fee. One advantage of this is the ability to make and receive calls as one would at home, anywhere in the world, at no extra cost. As calls go via IP, this does not incur charges as call diversion does via the PSTN, and the called party does not have to pay for the call.

For example, somebody may call someone on a number with a U.S. area code, but one could be in London, and if someone were to call another number with that area code, it would be treated as a local call, regardless of where that person is in the world. However, the broadband phone is likely to complement, rather than replace a PSTN line, as it still needs a power supply, while calling the U.S. emergency services number 911, may not automatically be routed to the nearest local emergency dispatch center, and would be of no use for subscribers outside the U.S.

Another challenge for these services is the proper handling of outgoing calls from fax machines, TiVo/ReplayTV boxes, satellite television receivers, alarm systems, conventional modems or FAXmodems, and other similar devices that depend on access to a voice-grade telephone line for some or all of their functionality. At present, these types of calls sometimes go through without any problems, but in other cases they will not go through at all. And in some cases, this equipment can be made to work over a VoIP connection if the sending speed can be changed to a lower bits per second rate. If VoIP and cellular substitution becomes very popular, some ancillary equipment makers may be forced to redesign equipment, because it would no longer be possible to assume a conventional voice-grade telephone line would be available in almost all homes in North America and Western-Europe. The TestYourVoIP website offers a free service to test the quality of or diagnose an Internet connection by placing simulated VoIP calls from any Java-enabled Web browser, or from any phone or VoIP device capable of calling the PSTN network.

Corporate and telco use

Although few office environments and even fewer homes use a pure VoIP infrastructure, telecommunications providers routinely use IP telephony, often over a dedicated IP network, to connect switching stations, converting voice signals to IP packets and back. The result is a data-abstracted digital network which the provider can easily upgrade and use for multiple purposes.

Corporate customer telephone support often use IP telephony exclusively to take advantage of the data abstraction. The benefit of using this technology is the need for only one class of circuit connection and better bandwidth use. Companies can acquire their own gateways to eliminate third-party costs, which is worthwhile in some situations.

VoIP is widely employed by carriers, especially for international telephone calls. It is commonly used to route traffic starting and ending at conventional PSTN telephones.

Many telecommunications companies are looking at the IP Multimedia Subsystem which will merge Internet technologies with the mobile world, using a pure VoIP infrastructure. It will enable them to upgrade their existing systems while embracing Internet technologies such as the Web, email, instant messaging, presence, and video conferencing. It will also allow existing VoIP systems to interface with the conventional PSTN and mobile phones.

Electronic Numbering (Enum) uses standard phone numbers (E.164), but allows connections entirely over the Internet. If the other party uses Enum, the only expense is the Internet connection.

Legal

As the popularity of VoIP grows, and PSTN users switch to VoIP in increasing numbers, governments are becoming more interested in regulating VoIP in a manner similar to PSTN services.

In the US, the FCC now requires all VoIP operators who don't support E911 to attach a sticker warning that traditional 911 services aren't available. The FCC recently required VoIP operators to support CALEA wiretap functionality [1]. A proposed bill, currently in Congress, proposes adding more traditional PSTN regulations, such as number portability and universal service fees.

Technical details

Protocols

Most standards-based solutions use either the H.323 or Session Initiation Protocol (SIP) protocols. A number of proprietary designs also exist.

A notable package on the Enterprise IP PBX side is sipX - The Open Source SIP PBX for Linux from SIPfoundry, a fully SIP compliant implementation running on Linux and available for free.

Signaling protocols:

Session Initiation Protocol (SIP): defined by the IETF, newer than H.323
H.323: defined by the ITU-T
Megaco (a.k.a. H.248) and MGCP: both media gateway control protocols
Skinny Client Control Protocol: proprietary protocol from Cisco
MiNET: proprietary protocol from Mitel
CorNet-IP: proprietary protocol from Siemens
IAX: the Inter-Asterisk eXchange protocol used by the Asterisk open source PBX server and associated client software
Skype: a proprietary peer-to-peer protocol used in the Skype application
Jajah: a proprietary peer-to-peer protocol used in the Jajah SIP and IAX compatible webphone

Several different speech codecs can be used for stream audio compression. Commonly used codecs for VoIP traffic include G.711 and G.729, both ITU-T-specified codecs.

Related concepts

External links

FCC VoIP Information from the FCC
Internet Telephony Magazine - educational VoIP magazine
Voxilla - VoIP News and forum
SIPfoundry – Open Source community dedicated to VoIP solutions based on SIP
How to Distribute VoIP Throughout a Home Instructions on how to use your existing home telephone wiring with a VoIP service.
VoIP Reviews Compares VoIP companies
VOIP for Dummies How to make best use of VOIP