QoS Performance Measures

To achieve a QoS for a certain application, the application requirements must be quantified in terms of parameters that identify the target performance level. Such a level is normally measured in terms of throughput, delay, jitter, and packet loss.

LTE identifies the following major quantitative parameters.

1. Throughput: Characterized through the Guaranteed Bit Rate, Maximum Bit Rate and Aggregate Maximum Bit Rate.
   • a) The Guaranteed Bit Rate (GBR): Network resources allocated based on GBR are fixed and do not change after bearer establishment or modification. This is hence a guaranteed service data flow.
   • b) The Maximum Bit Rate (MBR): This parameter limits the bit rate that can be expected to be provided to GBR bearer, and is enforced by network shaper to restrict the traffic to its maximum bit rate agreement.
   • c) Aggregate Maximum Bit Rate (AMBR): This parameter is used for non-GBR flows, and has two types, APN-AMBR and UE-AMBR. The APN-AMBR (Access Point Name-AMBR) is a subscription parameter stored at the HSS per APN. The HSS defines a QCI for each PDN (identifiable by an individual PDN identifier) and an APN-AMBR for each ARP. The APN-AMBR parameter refers to the maximum bit rate that can be consumed by all non-GBR bearers and all PDN connections of this APN. This parameter is enforced by P-GW in the downlink and by both UE and P-GW in the uplink. The UE-AMBR parameter, on the other hand, refers to the maximum bit rate allowed for all non-GBR bearer aggregates for the respective UE. The parameter is enforced in both the downlink and the uplink.

   Note that GBR and MBR are defined per bearer while the AMBR parameters are defined per a group of bearers. All throughput parameters have two components, one for downlink and another for uplink.

2. Delay: Specified by the packet delay budget. LTE defines nine categories for delay, with 50 ms being tightest and 300 ms being the slackest. The latter value is used for delay tolerant applications.
3. Packet Loss: Defined as the Packet Error Loss Rate, and is similar to the packet delay budget in having nine categories with 10⁻⁶ being best and 10⁻² being the worst.
4. Priority: Specified by the Allocation/Retention Priority (APR) parameter, which is used to indicate the priority of both allocation and retention of the service data flow. The APR dictates whether a bearer establishment/modification request can be accepted or rejected in the event of conflicts in demand for network resources. At the time of exceptional network resources limitations, such as handover, ARP can be used by the eNodeB to drop a flow with a lower ARP to free up capacity. ARP, however, has no effect on the network treatment received by the flow once the flow is successfully established.