Message-Priority Indication over GTP-C

An overloaded node performs message prioritization when handling incoming messages during an overloaded condition based on the relative GTP-C message priority signaled in the GTP-C header.

When message throttling is performed:

  • GTP requests related to priority traffic (eMPS as described in 3GPP TS 22.153) and emergency have the highest priority. Depending on regional/national requirements and network operator policy, these GTP requests are the last to be throttled when applying traffic reduction. The priority traffic is exempted from throttling due to GTP overload control up to the point where the requested traffic reduction cannot be achieved without throttling the priority traffic.

  • For other types of sessions, message throttling considers the relative priority of the messages so that low priority messages are considered for throttling before the other messages. The relative priority of the messages is derived from the relative priority of the procedure for which the message is being sent (as specified in clause 12.3.9.3.2) or derived from the session parameters such as APN and ARP.

The high priority messages are given lower preference to throttle and low priority messages are given higher preference to throttle. An overloaded node also applies these message prioritization schemes when handling incoming initial messages during an overloaded condition, as part of the self-protection mechanism.

A sending GTP-C entity determines the relative message priority to signal in the message according to either procedure based or session parameters. If the message affects multiple bearers (for example, Modify Bearer Request), the relative message priority considers the highest priority ARP among all the bearers.

A GTP-C entity sets the same message priority in a Triggered message or Triggered Reply message as received in the corresponding Initial message or Triggered message respectively. For incoming GTP-C messages that do not have a message priority in the GTP-C header, the receiving GTP-C entity:

  • Applies a default priority if the incoming message is an Initial message.

  • Applies the message priority sent in the Initial message or Triggered message if the incoming message is a Triggered or Triggered Reply message respectively.

The nodes in the network homogenously support this feature; otherwise an overloaded node processes initial messages received from the non-supporting nodes according to the default priority and processes initial messages received from the supporting nodes according to the message priority signaled in the GTP-C message.

Message-Prioritization based on Session Parameters

Message prioritization is also performed based on the session parameters such as APN and ARP. The procedures and messages associated with the higher priority sessions are given lesser preference while throttling, as compared to the procedures and messages associated with the lower priority sessions. Within each group of sessions, the messages are further prioritized based on the category of the procedure for which the message is being sent.