The tunnel management procedures are used to create, update, and delete GTP tunnels in order to route IP PDUs between an MS and an external PDN via the GSNs.
The PDP context 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.
Tunnel management procedures are defined to create, update, and delete tunnels within the GPRS backbone network. A GTP tunnel is used to deliver packets between an SGSN and a GGSN. A GTP tunnel is identified in each GSN node by a TEID, an IP address, and a UDP port number.
|Message Type||Used by||Description|
|Create PDP Context Request/ Response||GTP-C||Sent from an SGSN to a GGSN node as part of a GPRS PDP Context Activation procedure or the Network-Requested PDP Context Activation procedure. A valid request initiates the creation of a tunnel.|
|Update PDP Context Request/ Response||GTP-C||Used when PDP Context information changes, such as when a mobile device changes location.|
|Delete PDP Context Request/ Response||GTP-C||Used to terminate a PDP Context, and confirm the context has been deleted.|
|Create AA PDP Context Request/ Response||GTP-C||Sent as part of the GPRS Anonymous Access PDP Context Activation. It is used to create a tunnel between a context in the SGSN and a context in the GGSN.|
|Delete AA PDP Context Request/ Response||GTP-C||Sent as part of the GPRS PDP Anonymous Access Context Deactivation procedure to deactivate an activated PDP Context. It contains Cause and Private Extension Information Elements|
|Error Indication||GTP-U||Sent to the GGSN when a tunnel PDU is received for the following conditions:
— No PDP context exists
— PDP context is inactive
— No MM context exists
— GGSN deletes its PDP context when the message is received.
|PDU Notification Request/ Response/ Reject Request/ Reject Response||GTP-C||When receiving a Tunneled PDU (T-PDU), the GGSN checks if a PDP context is established for the given PDP address. If no PDP context has been established, the GGSN may initiate the Network-requested PDP Context Activation procedure by sending a PDU Notification Request to the SGSN.
Reject Request - Sent when the PDP context requested by the GGSN cannot be established.