PDP Context
The packet data protocol (PDP; e.g., IP, X.25, FrameRelay) context is a data structure present on both the serving GPRS support node (SGSN) and the gateway GPRS support node (GGSN) which contains the subscriber's session information when the subscriber has an active session. When a mobile wants to use GPRS, it must first attach and then activate a PDP context. This allocates a PDP context data structure in the SGSN that the subscriber is currently visiting and the GGSN serving the subscriber's access point. The data recorded includes
- Subscriber's IP address
- Subscriber's IMSI
- Subscriber's
- Tunnel Endpoint ID (TEID) at the GGSN
- Tunnel Endpoint ID (TEID) at the SGSN
The Tunnel Endpoint ID (TEID) is a number allocated by the GSN which identifies the tunnelled data related to a particular PDP context.
Several PDP contexts may use the same IP address. The Secondary PDP Context Activation procedure may be used to activate a PDP context while reusing the PDP address and other PDP context information from an already active PDP context, but with a different QoS profile. Note that the procedure is called secondary, not the resulting PDP contexts that have no such relationship with the one the PDP address of which they reused.
A total of 11 PDP contexts (with any combination of primary and secondary) can co-exist. NSAPI are used to differentiate the different PDP context.
Read more about this topic: GPRS Core Network
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