This section describes the 3GPP R12 GTP-C Load and Overload Control feature.
Use of the 3GPP R12 Load and Overload Control feature requires that a valid license key be installed. Contact your Cisco account or support representative for information on how to obtain a license.
The 3GPP R12 GTP-C Load and Overload Control feature is a licensed, optional feature which allows a GTP control plane node to send its load information to a peer GTP control plane node which the receiving GTP control plane peer node uses to augment existing GW selection procedure for the P-GW and S-GW. Load information reflects the operating status of the resources of the originating GTP control plane node.
Nodes using GTP control plane signaling may support communication of overload control information in order to mitigate overload situations for the overloaded node through actions taken by the peer node(s). This feature is supported over the S4, S11, S5 and S8 interfaces via the GTPv2 control plane protocol.
A GTP-C node is considered to be in overload when it is operating over its nominal capacity resulting in diminished performance (including impacts to handling of incoming and outgoing traffic). Overload control information reflects an indication of when the originating node has reached such a situation. This information, when transmitted between GTP-C nodes, may be used to reduce and/or throttle the amount of GTP-C signaling traffic between these nodes. As such, the overload control information provides guidance to the receiving node to decide upon the correct actions, which leads to mitigation towards the sender of the information.
To summarize, load control and overload control can be described in this manner:
- Load Control: Load control enables a GTP-C entity (for example, an P-GW/SAEGW/S-GW) to send its load information to a GTP-C peer (for example, an MME/SGSN, ePDG, TWAN) to adaptively balance the session load across entities supporting the same function (for example, an S-GW cluster) according to their effective load. The load information reflects the operating status of the resources of the GTP-C entity.
- Overload Control: Overload control enables a GTP-C entity becoming or being overloaded to gracefully reduce its incoming signaling load by instructing its GTP-C peers to reduce sending traffic according to its available signaling capacity to successfully process the traffic. A GTP-C entity is in overload when it operates over its signaling capacity, which results in diminished performance (including impacts to handling of incoming and outgoing traffic).
Load and Overload Factor Calculation Enhancement
In capacity testing and also in customer deployments it was observed that the chassis load factor for the 3GPP R12 Load and Overload Support feature was providing incorrect values even when the sessmgr card CPU utilization was high. The root cause is that when the load factor was calculated by taking an average of CPU utilization of sessmgr and demux cards, the demux card CPU utilization never increased more than the sessmgr card CPU utilization. As a result, the system did not go into the overload state even when the sessmgr card CPU utilization was high.
The 3GPP R12 Load/Overload Control Profile feature has been enhanced to calculate the load factor based on the higher value of similar types of cards for CPU load and memory. If the demux card's CPU utilization value is higher than the sessmgr card's CPU utilization value, then the demux card CPU utilization value is used for the load factor calculation.
A new CLI command, gtpc-system-param-poll interval , is introduced to configure different polling intervals for the resource manager so that the demuxmgr can calculate the load factor based on different system requirements.
Relationships to Other Features
Note the following before configuring the GTPP R12 GTP-C Load and Overload Control feature:
- One of the following services
must be configured on the node before GTP-C Load and Overload Control can be
- Once configured, the GTP-C Load and Overload Control profiles must be associated with a P-GW, SAEGW, or S-GW service to function properly in the network.