A modern voice communication SIP protocol is widely used to make calls in the Internet. However, the final subscriber is mostly interested not in the very SIP standard but in the SIP telephony conception based on it.
One one hand, all traditional conveniences for making telephone calls, compatibility with the international subscription base and the procedure of dialing numbers are kept.
The SIP-telephony allows making telephone calls between subscribers connected to the Internet and telephone network (and vice versa). Is this a change of the traditional telephone communication (wire and mobile)? No, but this is a good addition to it. The connection to service is fast, easy and cheap.
SIP is a protocol of administering and signalizing the level of additions. It serves for organizing, modifying and ending sessions in connection with one or several subscribers. These can be multimedia conferences via the Internet, distance education sessions, calls of packet telephony and distribution of multimedia signals. SIP allows establishing connections both for subscribers and self-adjustments, for instance, such as archiving servers. This protocol can be used for initiating communication sessions, connecting additional participants to communication sessions established in other ways or for establishing multilateral communication with the help of MCU.
SIP protocol transparently supports the service of transforming names and services of redirection providing the clients of ISDN and intellectual networks with an additional service, for example, the guaranty of personal mobility of subscribers. This protocol does not offer the services of administering conferences and does not prescribe the order of their realization. It does not set group addresses and does not reserve resources but allows transferring information needed for it into the called system. SIP solves the tasks of establishing and ending multimedia connections:
Location definition of the called party Identification of transmission environment type and its characteristics Definition of possibility to establish a communication session with a chosen subscriber Making of call The following administering of it
Only one order – the presence of a high-speed connection to the Internet, for instance, ADSL, which is not a rarity today. There could be several reasons for using SIP-telephony:
Making additional lines for outgoing calls via the Internet; Freeing already available city lines for incoming calls; Joining the telephone systems of several offices into one corporate network; Organizing a mobile (distant) working place of a company head or member; Organizing a new working place for a member without laying additional telephone wires; A considerable cut of expenses on intercity talks as well as fax transfer.
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