Section: 12.2.5.1.2 Parameters
Content: 12.2.5.1.2.1 Load Control Sequence Number The Load Control Sequence number contains a value that indicates the sequence number associated with the LCI IE. This sequence number shall be used to differentiate any two LCI IEs generated at two different instances by the same GTP-C entity. The Load Control Sequence Number shall be supported (if load control is supported) and shall always be present in the LCI IE. The GTP-C entity generating this information shall increment the Load Control Sequence Number whenever modifying some information in the Load Control Information IE. The Load Control Sequence Number shall not be incremented otherwise. The node may use the time, represented in an unsigned integer format, of the generation of the Load Control Information to populate the Load Control Sequence Number. When multiple instances of the LCI IE are provided in a message by a given GTP-C node, each of them shall contain the same Load Control Sequence Number value. This parameter shall be used by the receiver of the Load Control Information IE to properly collate out-of-order load control information, e.g. due to GTP-C retransmissions. This parameter shall also be used by the receiver of the LCI IE to determine whether the newly received load control information has changed compared to load control information previously received from the same node earlier. NOTE: The GTP-C sequence number cannot be used for collating out-of-order load control information as e.g. load control information may be sent in both GTP-C requests and responses, using independent GTP-C sequence numbering. If the receiving entity has already received and stored load control information from the peer GTP-C entity, the receiving entity shall update its load control information only if the Load Control Sequence Number received in the new load control information is higher than the stored value of the Load Control Sequence Number associated with the peer GTP-C entity. However due to roll-over of the Load Control Sequence Number or restart of the node, the Load Control Sequence Number may be reset to an appropriate base value by the peer GTP-C entity, hence the receiving entity shall be prepared to receive (and process) a Load Control Sequence Number parameter whose value is less than the previous value. 12.2.5.1.2.2 Load Metric The Load Metric parameter shall indicate the current load level of the originating node. The computation of the Load Metric is left to implementation. The node may consider various aspects, such as: the used capacity of the node based on activated bearers in relationship to maximum number of bearers the node can handle, the load that these active bearers produce in the node (e.g. memory/CPU usage in relationship to the total memory/CPU available, etc.). The Load Metric represents the current load level of the sending node as a percentage within the range of 0 to100, where 0 means no or 0% load and 100 means maximum or 100% load reached (i.e. no further load is desirable). The Load Metric shall be supported (if load control is supported). The Load Metric shall always be included in the Load Control Information. Considering the processing requirement of the receiver of the Load Control Information (e.g. handling of the new information, tuning the node selection algorithm to take the new information into account), the sender should refrain from advertising every small variation (e.g. with the granularity of 1 or 2), in the Load Metric which does not result in useful improvement in node selection logic at the receiver. During the typical operating condition of the sender, a larger variation in the Load Metric, e.g. 5 or more units, should be considered as reasonable enough for advertising the new Load Control Information and thus justifying the processing requirement (to handle the new information) of the receiver. NOTE: The range of the Load Metric, i.e. 0 to 100, does not mandate the sender to collect its own load information at every increment/decrement and hence to advertise the change of Load Metric with a granularity of 1%. Based on various implementation specific criteria, such as: the architecture, session and signalling capacity, the current load and so on, the sender is free to define its own logic and periodicity with which its own load information is collected. 12.2.5.1.2.3 List-of-APN_and_Relative Capacity The List-of-APN_and_Relative Capacity parameter contains a list of the tuple (APN, Relative Capacity) and this indicates one or more APNs for which the Load Control Information is applicable. The "APN" contains the name of the APN and the Relative Capacity indicates the resources configured for a given APN, compared to the total resources configured at the target PGW, as a percentage. When present in the LCI IE, the scope of the load information shall be the list of indicated APNs for the PGW that sends the load control information. In that case, the "Load Metric" shall be interpreted as an "APN-Load-Metric" and shall indicate the current resource utilization for the indicated APNs, as a percentage, as compared to the total resources configured for the indicated APNs at the target PGW. Its computation is implementation dependent and it has the same characteristics as "Load Metric". Only one instance of the List-Of-APN_and_Relative Capacity IE may be included within one Load Control Information instance. NOTE 1: The maximum number of tuples (APN, Relative Capacity) in the List-of-APN_and_Relative Capacity IE is set to 10. More than 10 occurrences of (APN, Relative Capacity), within one single instance of the List-of-APN_and_Relative Capacity IE is treated as protocol error by the receiver. If the List-of-APN_and_Relative Capacity IE has not been included, the scope of the Load Control Information shall be the entire PGW node (unless restricted by other parameters in the LCI IE). This parameter may be supported (if load control is supported) and shall be supported when APN level load control is supported. The receiver shall handle this parameter, when it is received, if it supports APN level load control. The receiver shall ignore a Load Control Information instance applicable for an APN, if it does not support APN level load control. NOTE 2: The PGW encodes the APN level load information and node level load information using different instance numbers in the message, so that the receiver will ignore the APN level load information, if it does not support the APN level load control feature. The maximum number of APNs, for which the PGW may advertise the Load Control Information, shall be limited to 10, i.e. the maximum number of occurrences of the tuple (APN, Relative Capacity) within and across various instances of the LCI IE shall be limited to 10, for a given PGW. Hence, if the PGW supports more than 10 APNs, it shall advertise the load control information for at most 10 of the most important APNs. In future, if needed, this limit may be increased to allow the PGW to advertise the load information for more APNs. In that case, the receiver not supporting the higher limit shall handle the first 10 APNs and shall ignore the load information for the remaining APNs. NOTE 3: The limit of the number of APN's takes into account various aspects such as: the processing and storage requirements at the overloaded node and the receiver, the number of important APNs for which load control advertisement will be necessary and interoperability between the nodes. When including load control information for some APN(s), the PGW shall also provide node level load control information by providing one instance of the Load Control Information without the List-of-APN_and_Relative Capacity parameter. A node selecting a PGW for a given APN shall apply the APN level load information, if available for that APN. If this parameter is not received for a given APN but it has been received for other APN(s) from the same PGW, then for this given APN, the node performing PGW selection shall calculate the load metric, as described in 3GPP TS 29.303[ Domain Name System Procedures; Stage 3 ]  [32], for the target PGW.