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Packet Intercept API

Convene Networks provides a set of packet intercept Application Program Interface (API) functions for ConveneGSC GTP Routing and Session Control.

Convene Networks, ConveneGSC, Packet Intercept API

cnvCallout provides these functions:

  • Inbound Callout: upon receipt of a GTP-C packet;
  • Outbound Callout: just prior to queuing a GTP-C packet for sending;
  • Invalid Packet Callout: upon receipt of an invalid/unsupported GTP-C packet;
  • Application Event Callout: upon significant application events.

With these callout functions, Convene Networks provides a C++ class to give access to the GTP packets.  An object pointer allows message modification.  The packet can be modified in place and/or forwarded/stored/logged for debug purposes.

The functions provided include:

  • Retrieval/setting of information from the transport (IP/UDP header removed);
  • Retrieval/setting of information in the GTP header;
  • Retrieval/setting of IE existing contents;
  • Retrieval of a local 64 bit transaction ID (from which the lower 32 are TEID).

These functions are above the GTP peer layer, so all action related to sequencing, retransmission, and duplicates are handled before (inbound) or after (outbound) the function is called.

These functions run in the thread of the application.  A mechanism is provided that allows the operator to configure the size of the thread pool(s) to enable tuning of the thread allocation based on the CPU load caused due to the packet intercept functions.

Incoming valid packets (not corrupted) will result in the inbound callout being invoked. Methods are provided to access, modify, and/or reject the packet.

Corrupted packets will result in a call to the invalid packet callout. Packets will be discarded upon return from this callout.

Missing Informational Elements (IEs) are not detected as part of the GTP layer processing.  These will be presented to the inbound callout prior to the IMSI mapping activities.  IMSI mapping will occur and result in creation of a new packet which will be sent to the appropriate peer according to the rules of IMSI mapping.

Prior to sending a packet, the outbound callout will be invoked with a message object representing the outbound packet.  Methods are provided to access, modify, and/or reject the packet.

Packets that are retransmitted by peers or ConveneGSC are detected and dropped in the GTP layer, so neither the inbound, outbound, nor the invalid packet callouts are invoked.

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