Thursday, February 10, 2011

VoIP (Voice over Internet Protocol)

  •  Voice over Internet Protocol (VoIP) is a general term for a family of transmission technologies for delivery of voice communications over IP networks such as the Internet or other packet-switched networks.
  •    Voice information over the Internet.VoIP involves sending voice information in digital form in discrete packets rather than by using the traditional circuit-committed protocols of the public switched telephone network (PSTN).
  •   Other terms frequently encountered and synonymous with VoIP are 
  •  IP telephony,
  •   Internet telephony,
  •   voice over broadband (VoBB),
  •   broadband telephony, and
  •   broadband phone. 
  •   Internet telephony refers to communications services — voice, facsimile, and/or voice-messaging applications — that are transported via the Internet, rather than the public switched telephone network (PSTN).
  • The basic steps involved in originating an Internet telephone call are conversion of the analog voice signal to digital format and translation of the signal into Internet protocol (IP) packets for transmission over the Internet; the process is reversed at the receiving end.
  • VoIP derives from the VoIP Forum, an effort by major equipment providers, including Cisco, VocalTec, 3Com, and Netspeak to promote the use of ITU-T H.323, the standard for sending voice (audio) and video using IP on the public Internet and within an intranet. The Forum also promotes the user of directory service standards so that users can locate other users and the use of touch-tone signals for automatic call distribution and voice mail.
Advantages of VoIP
A major advantage of VoIP and Internet telephony is that it avoids the tolls charged by ordinary telephone service.
  •   Most people use it for free. If you have a computer with a microphone and speakers, and a good Internet connection, you can communicate using VoIP for free. This can also be possible with the mobile and home phone.
  •   When it is used to completely replace the PSTN service, then it has a price. But this price is way cheaper than standard phone calls.
  •    Inexpensive and easy to use. Since it is simple, upgrading is relatively simpler too.
  •    You can integrate it with an existing phone connection.
  •    With VOIP PC-to-PC, calls are free no matter the distance and PC-to-Phone charges are nominal.
  •    For a monthly fee you may make unlimited free calls within a geographic area.
  •    A virtual number enables you to make calls from anywhere as long as a broadband connection is available.
  •    You may purchase a number in a geography area of your choice, which works out very cheap. If your relatives and friends live in Virginia and you moved to California, you may purchase a Virginia number and make local calls to your loved ones.
  •    You may access your VOIP account just like your email Id from any where in the world as long as you have an internet phone. This makes it easy for those who travel frequently to make calls frequently to those back at home at local call rates, no matter where they are.
  •  You may call or message or do both at the same time with VOIP services.

Problems with VoIP
  •   Loss of service during outages.
  •    Without power VOIP phones are useless, so in case of emergencies during power cuts it can be a major disadvantage.
  •    With VOIP emergency calls, it is hard to locate you and send help in time.
  •    Some times during calls, there may be periods of silence when data is lost while it is being unscrambled.
  •    Latency and traffic.
  •    No standard protocol is applicable.
  • The disadvantages of VOIP could be annoying, but their effects are relatively limited. The complaints of VOIP are usually tolerable if the callers are using a free service.
VoIP Protocols
  •  Real-Time Protocol (RTP) for transmitting audio and video packets between communicating computers.
  •   RTP also addresses issues like packet order and provides mechanisms (via the Real-Time Control Protocol, or RTCP, also defined in RFC 3550) to help address delay and jitter.
  •   One of the areas of concern for people communicating over the Internet is the potential a person to eavesdrop on communication.
  •   To address these security concerns, RTP was improved upon with the result being called Secure RTP (defined in RFC 3711).
  •   Secure RTP provides for encryption, authentication, and integrity of the audio and video packets transmitted between communicating devices.
  •   The protocols that are central to this process are referred to as call-signaling protocols, the most popular of which are
  •   H.323 and
  •   Session Initiation Protocol (SIP) and they both rely on static provisioning,
  and other protocols to find other users. 

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