How QoS is managed in LTE/EPS system

eNB manage traffic QoS requirement on two aspectsOn the radio interfaceOn the transport (backhaul)

A. QoS mechanisms in the radio part
1) Radio bearer control

QoS functionality in the RBC is to dynamically monitors the quality of service status of ongoing RBs based on the interaction with the MAC Scheduler. When quality of service requirements for an ongoing RBs are not fulfilled, QoS invokes the RBC function to release or to reconfigure the corresponding radio bearer.

2) Scheduling

MAC scheduler plays an important role to achieve required QoS for each radio bearer.Scheduling priority is a continuous function of QCI, GBR, delay budget, etc. For example, below formula can be used when calculating scheduling metric:M = R * Mqos * Mqci / (T^Alpha)

R is the expected/wanted bit rate

Mqos is the QoS metric

Mcqi is the QCI metric

T is the actual bit rate in the last scheduling period

Alpha is a fairness factor, Alpha = 0 means the system doesn't care what has been achieved, scheduling metric is only determined by the demand, therefore it is unfair among users;

Alpha > 1 means the system gives more weight to each UE's the performance, finding fairness among users.

3) Admission control

4) Congestion control5） ICICBasically, like AC and CC, ICIC function module just provide constraints to scheduling function.

B. QoS mechanisms in the transport

1) DiffServ uses the 6-bit Differentiated Services Code Point (DSCP) field in the header of IP packets for packet classification purposes. eNB maps QCI against DSCP so that the IP packets are marked with corresponding QoS requirements.

2) Mapping DSCP with P-bit in VLAN. In case of VLAN is supported, QoS priority is preserved as P-bit (7 bit) within a VLAN ID.