Avancerede Datanet VoIP

Avancerede Datanet

Ole Brun Madsen

Voice over IP (VoIP)

IP telephony switches enable voice calls to be made within Internet Protocol (IP) networks, such as the public Internet or the private IP network of a large organisation, and between IP networks and the Public Switched Telephone Network (PSTN).

Calls can be made between IP network terminals, between PSTN telephones and IP terminals, or between PSTN telephones across an IP network.

To interoperate with the PSTN, an IP telephony switch must support the Signaling System 7 (SS7) protocol, either on-board or via an off-board interworking device. SS7 is used to efficiently set up calls in the PSTN and to query PSTN database servers. The support of SS7 by IP telephony switches represents an important step in the integration of the PSTN and IP data networks.

The IP-Telephony Switch

Voice over Internet Protocol (VoIP)

Voice over Internet Protocol (VoIP)

Voice over Internet Protocol (VoIP)

Voice over Internet Protocol (VoIP)

The TIPHON projet, ETSI work on Voice over IP

Recognizing the urgent need for common solutions, ETSI, has established the project TIPHON (Telecommunications and Internet Protocol Harmonization Over Networks). The project's objective is to support the market for voice communication and related voiceband communication (such as facsimile) between users. It will ensure that users connected to IP based networks can intercommunicate with users in Switched Circuit Networks (SCN - such as PSTN, ISDN and GSM.

The support comes in the production of appropriate ETSI technical specifications and reports. In addition, the activity will include validation and demonstrations, in order to confirm the appropriateness of the solutions proposed.

Given the universal nature of IP networks, the prime goal is to produce global standards. As ETSI is essentially a European body, it recognizes that co-operation with relevant groupings in ITU-T and IETF is essential.

The TIPHON projet, ETSI work on Voice over IP

“Black Box”: E.164 / IP Resolution 123456789012 - 172.27.0.1 … ... 1) 2) 3) 4)

H.323

In 1996, ITU ratified the H.323 specification which defines how delay-sensitive voice and video traffic is transported over local area networks. In 1998 ITU approved the H.323 Revision 2 for use in wide area networks.

Operating H.323 terminals over a wide area network may result in poor performance due to the lack of quality-of-service (QoS) guarantees in e.q. IP networks.

In the Internet, congestion due to inadequate bandwidth often leads to long delays in the delivery of time-sensitive packets. For voice data packets which are lost or discarded result in gaps, silence, and clipping in real-time audio playback.

To support a real-time QoS, the Internet Engineering Task Force (IETF) has proposed a new IP-based protocol called the Resource Reservation Protocol (RSVP). Using RSVP, both real time and non-real time applications can specify an appropriate QoS over the shared bandwidth of the Internet. (For more information, refer to RFC 1633.)

ITU Series H: Audiovisual and multimedia systems

Systems and terminal equipment for audiovisual services

H.310 (11/96) Broadband audiovisual communication systems and terminals H.310 Corr.1 (2/98)

H.320 (7/97) Narrow-band visual telephone systems and terminal equipment

H.321 (2/98) Adaptation of H.320 visual telephone terminals to B-ISDN environments H.322 (3/96) Visual telephone systems and terminal equipment for local area networks which provide a guaranteed quality of service

H.323

H.323 entities may be used in point-to-point, multipoint, or broadcast (as described in Recommendation H.332) configurations. They may interwork with H.310 terminals on B-ISDN, H.320 terminals on N-ISDN, H.321 terminals on B-ISDN, H.322 terminals on Guaranteed Quality of Service LANs, H.324 terminals on GSTN and wireless networks, V.70 terminals on GSTN, and voice terminals on GSTN or ISDN through the use of Gateways.

H.323 entities may be integrated into personal computers or implemented in stand-alone devices such as videotelephones.

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