Mobile Backhaul

8.7 LTE

8.7.1 QoS Architecture

With LTE, the quality of service concept is simpler than that of the 3G system. A default bearer supports IP connectivity for basically any service. When the indicated quality of service need is different than that which the default bearer offers, a dedicated bearer is set up – provided that the system has resources for the new bearer.

A traffic flow template (TFT) defines which user flows can be mapped to which bearers. User flows that have similar requirements, can use the same bearer. User flows with differing requirements, will be mapped to different EPS bearers. Traffic flow template exists in the UE for the uplink, and in PDN GW for the downlink.

In addition to traffic flow template, service data flow (SDF) template is defined. This is related to Policy and Charging Control (PCC) rules. SDF may e.g. provide a finer granularity than TFT. SDF and TFT may also in practice be identical. SDF only exists in the core network.

Traffic mapped to the same EPS bearer receives the same QoS treatment. QoS functions in the LTE system include scheduling and queue management policy, RLC configurations (e.g. RLC mode) and a shaping policy.

With LTE, Quality of service Class Indicator (QCI), as the name implies, is one key indication for the QoS of the bearer. In transport Differentiated services codepoint (DSCPs) are available for carrying this information in the IP packets, based on the QCI.

8.7.2 Packet Flows and Bearers

EPS bearer provides the packet data ...