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Voice over IP (Voice over Internet Protocol)

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    Default Voice over IP (Voice over Internet Protocol)

    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.
    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 might 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.



    In general, phone service via VoIP costs less than equivalent service from traditional sources. Some cost savings are due to using a single network to carry voice and data, especially where users have existing under-utilized network capacity they can use for VoIP at no additional cost. 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 Google Talk, Gizmo Project, Skype, TheGlobe, Yahoo! Messenger, MSN Messenger, and GossipTel.


    VoIP makes easy some things that are difficult 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 video conversation, message or data file exchange in parallel with the conversation, audio conferencing, managing address books and p***ing information about whether others (e.g. friends or colleagues) are available online to interested parties.


    VoIP technology still has a few shortcomings that have led some to believe that it is not ready for widespread deployment. However, many industry analysts predicted that 2005 was the "Year of Inflection," where more IP PBX ports shipped 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), and jitter. They are faced with the problem of restructuring streams of received IP packets, which can come in any order and have packets delayed or missing, to ensure that the ensuing audio stream maintains a proper time consistency. This problem has been addressed by Ubicom with their StreamEngine Technology.
    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, due to network routing time (buffering, switching) and transmission distances (more relevant under satellite links).


    Conventional telephones 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. 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 the 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 transferred 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, typically require the use of a computer, so they are limited to single point of calling, though handsets are now available for so they can be used without a PC. 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.
    Last edited by Admin; 26th September 2015 at 07:29 AM.

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