Message Prioritization Based on Procedures
Message prioritization is performed based on the relative priority of the procedure for which the message is being sent. Procedures are grouped into various categories and each of these categories are assigned a priority. In addition, within a given category of procedures, messages can be further prioritized based on session parameters, such as APN, QCI, ARP or LAPI.
Messages with a high priority are given lower preference to throttle and messages with low priority are given higher preference to throttle. The grouping of the procedures isn’t performed based on an individual GTP-C entity but while considering all the procedures in general. A GTP-C entity considers the procedures applicable to it and prioritizes message throttling based on the category of the procedure. The categories are listed in decreasing order of priority with category 1 having the highest priority. For each category, a nonexhaustive list of messages is provided. Any existing or newly defined message in future is considered based on the category of the procedure for which the message is sent. Following are the categories of a procedure:
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UE session mobility within and across 3GPP or non-3GPP access—Procedures involving active or idle mode UE mobility, such that GTP-C signalling involved are classified under this category. Some examples are X2 or S1 based handover with or without an SGW change, TAU or RAU with a change of MMEor SGSN with or without an SGW change, and 3GPP access to trusted non-3GPP access handover. Throttling of these messages during the procedures related to UE session mobility results in the failure of the corresponding procedures. This failure can cause PDN disconnection or the interruption of the services. As a result, the following messages, when sent during the procedures belonging to this category, must be considered with the highest priority. Hence, these messages are given the lowest preference to throttle.
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Create Session Request.
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Create Session Request with "handover" indication bit set.
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Modify Bearer Request.
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Modify Bearer Request with "handover" indication bit set.
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Modify Access Bearer Request.
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Release of PDN connection or bearer resources—Procedures resulting in the deactivation of an existing PDN connection, the deactivation of bearers or of data forwarding tunnel of an UE leads to freeing up of the resources at the overloaded node. These procedures ease the overload situation as the freed up resources can be used for serving the remaining of the UEs. Hence, the following messages that belong to this category and cause the deactivation of PDN connection or bearers or data forwarding tunnels, must be treated with the next lower level of priority. Hence, these messages are given the corresponding preference whilst throttling:
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Delete Session Request.
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Delete Bearer Request.
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Delete Bearer Command.
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Delete Indirect Data Forwarding Tunnel Request.
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Miscellaneous session management procedures—This category consists of the session management procedures, except the PDN connection creation and bearer creation or modification procedures. Some examples are location reporting, when it isn’t combined with other mobility procedures and Service request and S1 release procedure. These procedures do not impact the ongoing service of the UE. Hence, the following messages when sent during the procedures identified under this category, must be treated with the next lower level of priority. Hence, these messages are given the corresponding preference whilst throttling.
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Release Access Bearer Request.
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Modify Bearer Request.
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Change Notification.
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Suspend Notification.
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Resume Notification.
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Request for new PDN Connection or bearer resources or modification of existing bearer resources—This category consists of the procedures requesting the creation of PDN connection, creation or modification of bearers, or creation of data forwarding tunnel. Throttling of the messages belonging to this category cause denial of new services while continuing with the existing services. In this overload condition, an overloaded node, due to lack of resources, isn’t able to provide new services while trying to maintain the existing services. When the following messages are sent during the procedures belonging to this category are considered with the lowest level of priority. Hence, these messages are given highest preference to throttle:
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Create Session Request during PDN connection request.
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Create Bearer Request.
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Update Bearer Request.
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Bearer Resource Command.
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Modify Bearer Command.
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Create Indirect Data Forwarding Tunnel Request.
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Downgrade the DSCP marking of the data packets for the session when quota exhausts.
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