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service access point identifier (SAPI)

  1. Service Access Point Identifier (SAPI) represents an access point to a specific service in the link layer in the D-channel protocol. The SAPI identifier establishes a relationship to an instance in the network layer. In the D-channel protocol, four possible instances or services of layer 2 (SAPI) are defined for the terminal equipment, which are expressed in the 64 possible SAPI values. These SAPI values are permanently assigned to the services of the data link layer: SAPI-0 is used for signaling, SAPI-16 for packet-oriented data transfer, SAPI 32 to 47 are reserved for national purposes, and SAPI 63 for management functions such as TEI allocation or the formation of SAPI groups.

  2. In Link Access ProcedureSDH (LAP-S), the Service Access Point Identifier (SAPI) is a 2-bytedata field in which the IP protocol to be transported is entered.

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Englisch: service access point identifier - SAPI
Updated at: 03.03.2008
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