The Gn-Gp SGSN now supports EPC QoS parameters during PDP Activation/Modification procedures. Support is added for Evolved-ARP, APN-AMBR and UE-AMBR QoS parameters. The purpose of adding this support is to achieve end to end synchronization of QoS parameters during IRAT (3G/4G) mobility procedures. In previous releases it was observed that there is no synchronization between QoS parameters during TAU/RAU mobility from a 4G scenario to a 3G scenario or vice versa.
The EPC QoS attributes now supported Gn SGSN can be briefly described as below:
Evolved-ARP (E-ARP): Evolved allocation or retention priority specifies the relative importance of a Radio Access Bearers as compared to other Radio Access Bearers for allocation or retention of the Radio access bearer. The EPC uses Evolved ARP, which has priority level ranging from "1" up to "15". Additionally, evolved ARP comprises of pre-emption capability and pre-emption vulnerability. The preemption capability information defines whether a bearer with a lower priority level should be dropped to free up the required resources. The pre-emption vulnerability information indicates whether a bearer is applicable for such dropping by a preemption capable bearer with a higher priority value.
APN-AMBR (per APN Aggregate Maximum Bit Rate): The APN-AMBR limits the aggregate bit rate that can be provided across all Non- GBR PDP contexts of the same APN (for example, excess traffic may get discarded by a rate shaping function). Each of those Non-GBR PDP contexts can potentially utilize the entire APN AMBR (for example, when the other Non- GBR PDP contexts do not carry any traffic). The PGW enforces the APN AMBR in downlink. Enforcement of APN AMBR in uplink may be done in the UE and additionally in the PGW.
UE-AMBR: The UE AMBR limits the aggregate bit rate that can be provided across all Non-GBR PDP contexts of a UE (for example, excess traffic may get discarded by a rate shaping function). Each of the Non-GBR PDP contexts can potentially use the entire UE AMBR (for example, when the other Non-GBR PDP contexts do not carry any traffic). The GBR (real-time) PDP contexts are outside the scope of UE AMBR. The RAN enforces the UE AMBR in uplink and downlink.
With this feature enhancement the SGSN now supports the following functionalities:
- EPC QoS parameters for Gn/Gp interface activated PDPs are supported.
- The Gn-Gp SGSN reads the EPC QoS parameters from the HLR/HSS and the user.
- The Gn-Gp SGSN now performs capping of the QoS parameters and sends the negotiated values towards the GGSN and RAN.