Q.931

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The Q.931 recommendation of ITU-T (formerly CCITT) describes layer 3 of the protocol ( ISDN user-network interface layer 3 specification for basic call control ) and is used for signaling with ISDN and H.323 .

A Q.931 frame consists of:

  • Protocol discriminator (PD), protocol discriminator
The PD indicates which signaling protocol is used, for example DSS1 or FTZ 1 TR 6 .
  • Call reference value (CR), connection identification
The CR value is used to address different, simultaneously existing connections. The CR value is retained for the duration of a connection and is only valid locally.
  • Message type (MT), message type
The MT value is used to provide information about the content of the message, the information elements. There are message types for establishing a connection , for disconnecting a connection and for controlling service features.
  • Information elements (IE), information elements
The information elements are used to provide precise information on the transmitted message. The IE value consists of the parts IE length, IE name and IE content.

literature

  • Jonathan Davidson, James Peters: Voice over IP Basics. Markt + Technik Verlag, Munich 2000, ISBN 3-8272-5800-6 .
  • John G. van Bosse, Fabrizio U. Devetak: Signaling in Telecommunication Networks. Second Edition, A John Wiley & Sons Inc, New Jersey 2007, ISBN 978-0-471-66288-4 .
  • Bruce Hartpence: Packet Guide to Voice over IP. O'Reilly Media Inc, Sebastopol 2013, ISBN 978-1-449-33967-8 .
  • Wolf-Dieter Haaß: Handbook of the communication networks. Introduction to the basics and methods of communication networks, Springer Verlag Berlin Heidelberg, Berlin Heidelberg 1997, ISBN 978-3-642-63825-1 .

Web links