EPS Bearer - PART2

In this article we will discuss about Bearer Level QoS Parameters:

The EPS bearer QoS profile includes the parameters QCI, ARP, GBR and non-GBR. The QoS parameters which are applied to aggregated set of EPS bearers are APN-AMBR and UE-AMBR.

The QCI is scalar that is used as a reference to node specific parameters that control packet forwarding treatment ( e.g. scheduling weights, admission thresholds, queue management thresholds, link layer protocol configurations etc) and that have been pre-configured by the operator owning the node (e.g. eNodeB). The characterstics describe the packet forwarding treatment that an SDF aggregate  receives edge-to-edge between UE and PCEF in terms of the following characteristics:
1. Resource Type (GBR and non-GBR)
2. Priority
3. Packet Delay Budget (PDB)
4. Packet Error Loss Rate (PELR)

The one-to-one mapping of standardized QCI values to a standardized characterstics is as below:

The Resource Type determines if dedicated network resources related to a service or bearer level Guaranteed Bit Rate (GBR) value are permanently allocated (e.g. by an admission control function in a radio base station). GBR SDF aggregates are therefore typically authorized "on demand" which requires dynamic policy and charging control. A Non GBR SDF aggregate may be pre-authorized through static policy and charging control.

The Packet Delay Budget (PDB) defines an upper bound for the time that a packet may be delayed between the UE and the PCEF. For a certain QCI the value of the PDB is the same in uplink and downlink. The purpose of the PDB is to support the configuration of scheduling and link layer functions (e.g. the setting of scheduling priority weights and HARQ target operating points).

Every QCI (GBR and Non-GBR) is associated with a Priority level. Priority level 1 is the highest Priority level. The Priority levels shall be used to differentiate between SDF aggregates of the same UE, and it shall also be used to differentiate between SDF aggregates from different UEs. Via its QCI an SDF aggregate is associated with a Priority level and a PDB. Scheduling between different SDF aggregates shall primarily be based on the PDB. If the target set by the PDB can no longer be met for one or more SDF aggregate(s) across all UEs that have sufficient radio channel quality then Priority shall be used as follows: in this case a scheduler shall meet the PDB of an SDF aggregate on Priority level N in preference to meeting the PDB of SDF aggregates on Priority level N+1 until the priority N SDF aggregate's GBR (in case of a GBR SDF aggregate) has been satisfied.

The Packet Error Loss Rate (PELR) defines an upper bound for the rate of SDUs (e.g. IP packets) that have been processed by the sender of a link layer protocol (e.g. RLC in E‑UTRAN) but that are not successfully delivered by the corresponding receiver to the upper layer (e.g. PDCP in E‑UTRAN). Thus, the PELR defines an upper bound for a rate of non congestion related packet losses. The purpose of the PELR is to allow for appropriate link layer protocol configurations (e.g. RLC and HARQ in E‑UTRAN). For a certain QCI the value of the PELR is the same in uplink and downlink.

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