6.2.15 Multimedia Priority Service Congestion Control Procedures

23.3333GPPMultimedia Resource Function Controller (MRFC) - Multimedia Resource Function Processor (MRFP) Mp interface: Procedures descriptionsRelease 17TS

6.2.15.1 General

The MRFC and MRFP may support the priority treatment of a call/session identified as an MPS call/session. This clause describes the Mp signalling procedures and their interactions with SIP signalling in the control plane and with user plane procedures to support the requirements for MPS. These Mp signalling procedures may or may not apply depending on the network configuration (e.g. whether the MRFP is shared by multiple MRFCs or whether the MRFC controls multiple MRFPs for a given route – Media Gateway Group).

The MRFC can receive a SIP INVITE with MPS priority information (see 3GPP TS 23.228 [1], clause 5.21).

6.2.15.2 MRFP Resource Congestion in ADD response, request is queued

If the MRFC requests a resource via the Reserve and Configure IMS Resources procedure or Reserve IMS Resources procedure and receives an error indicating that the requested resource could not be seized (e.g. H.248 error code #510 "insufficient resources") and the MRFC does not have an alternative MRFP through which it can route the call/session, the MRFC queues the priority call/session and gives it priority over any further Reserve and Configure IMS Resources or Reserve IMS Resources procedures for lower priority calls/sessions towards this MRFP until the requested resource for this queued call/session is successfully seized. The example sequence is shown in Figure 6.2.15.2.1.

Figure 6.2.15.2.1: Request to Reserve MPS priority call resources when MRFP is congested

6.2.15.3 MRFP Resource Congestion in ADD response, MRFC seizes new MRFP

If the MRFC requests a resource via the Reserve and Configure IMS Resources procedure or Reserve IMS Resources procedure and receives an error indicating that the requested resources could not be seized due to congestion (e.g. H.248 error code #510 "insufficient resources") and Media Gateway Groups are implemented the MRFC seizes a new MRFP from the same Media Gateway Group before resorting to any queuing of the priority call/session (as described in 6.2.15.2) to enable the MPS call/session to proceed as early as possible.

6.2.15.4 MRFP Priority Resource Allocation

If the MRFP supports the Priority information (determined through provisioning or package profile), the MRFC requests a resource via the Reserve and Configure IMS Resources procedure or Reserve IMS Resources procedure and includes the Priority information. The MRFP may then provide priority allocation of resources once a congestion threshold is reached. The example sequence is shown in Figure 6.2.15.4.1. If the MRFP is completely congested it shall indicate this to the MRFC as described in 6.2.15.2.

Figure 6.2.15.4.1: Request to reserve MPS priority call resources when MRFP is congested, priority resources are allocated

6.2.15.5 MRFP Priority User Data marking

The MRFC may request the streams associated to an MPS call/session to be marked with certain priority code point. The MRFP shall then mark each IP packet header accordingly. The example sequence is shown in Figure 6.2.15.5.1.

Figure 6.2.15.5.1: Request to reserve IMS resources and apply DSCP marking for MPS

The MRFP may also provide priority allocation for resources requested via a subsequent Configure IMS Resources procedure not including Priority information if the related context has been marked with priority information during the Reserve IMS Resources procedure or Reserve and Configure IMS Resources procedure.