Feature Description

Important

The GTP-C Load and Overload Control is an optional feature.

The SMF uses the system load information to determine the operating status of the resources of the GTP-C entity. This information, when sent to the GTP-C peers, helps to balance the session load adaptively across entities supporting the same function based on their effective load.

A GTP-C overload occurs when the number of incoming requests exceeds the maximum request throughput supported by the receiving GTP-C entity. The GTP-C is over UDP transport, and it relies on the retransmissions of unacknowledged requests. When a GTP-C entity experiences overload (or severe overload), the number of unacknowledged GTP-C messages exponentially increase leading to a node congestion or collapse. An overload or a node failure leads to an increase of the load on the other nodes in the network.

Overload of the core network nodes in the network results in service degradation. Improved load distribution over the network helps in addressing the overload issue.

Overload conditions can occur in various network scenarios. The following are some examples of GTP-C signaling-based scenarios which lead to GTP-C overload:

  • A traffic flood resulting from the failure of a network element, inducing a signaling spike.

  • A traffic flood resulting from many users performing TAU or RAU or from frequent transitions between idle and connected modes.

  • An exceptional event locally generating a traffic spike, for example, many calls (and dedicated bearers) being set up almost simultaneously.

  • Frequent RAT reselection due to scattered non-3GPP (for example, Wi-Fi) coverage or a massive mobility between a 3GPP and non-3GPP coverage. This operation may potentially cause frequent or massive intersystem change activities.

GTP-C overload may result in any of the following service impacts:

  • Emergency call drops

  • Loss of PDN connectivity (IMS, Internet, and so on) and associated services.

  • Loss of ability to set up and release radio and core network bearers necessary to support services, for example, GBR bearers.

  • Loss of ability to report the change in—

    • User information, for example, location information for emergency services and lawful intercept

    • RAT or QoS

  • Billing errors which result in loss of revenue.

GTP-C Load and Overload Control is a standards-driven feature. For standards compliance information, see the Standards Compliance section in this feature chapter.

GTP-C Load Control and Overload Control are complimentary concepts which can be supported and activated independently on the network.

This feature works both in a standalone deployment of SMF and an integrated deployment with cnSGWc.

Note

This feature works only when the SMF interworks with PGW-C (that is, the EPS network). The term "SMF" used in this chapter denotes the combination of both SMF and PGW-C.