Quality Of Service

Quality Of Service in EPS
http://beyond-3g-wireless.blogspot.com/

It has been a long time not blogging anything. Now it is time to give a kick start once again. Let us continue our discussion from the place where we left 2 months back

In previous topic we discussed about What is default Bearer & Dedicated Bearer?

Now let us try to understand about the various QOS parameters

An EPS Bearer is characterized by various QOS Parameters

* ARP (Allocation Retention Priority): The primary responsibility of ARP is to decide whether bearer establishment or modify request can be accepted or rejected during resource limitation. In this is case the priority level information of ARP is used to decide

In addition eNB uses ARP mechanism to decide which bearer to drop during resource limitations(for eg. Handover).

Refer Spec 23.401 /Sec 4.7.3
a) Video telephony is one use case where it may be beneficial to use EPS bearers with different ARP values for the same UE. In this use case an operator could map voice to one bearer with a higher ARP, and video to another bearer with a lower ARP. In a congestion situation (e.g. cell edge) the eNB can then drop the "video bearer" without affecting the "voice bearer". This would improve service continuity

b) The ARP may also be used to free up capacity in exceptional situations, e.g. a disaster situation. In such a case the eNB may drop bearers with a lower ARP priority level to free up capacity if the pre-emption vulnerability information allows this.

* GBR (Guranteed Bit Rate)
This parameter is applicable only for dedicated bearer services like voice or streaming.GBR is nothing but the guranteed bit rate that is expected by a dedicated bearer service
* MBR (Maximum Bit Rate)
This is to limit the bit rate that can be expected to be provided by dedicated bearer

From sec 4.7.4 /Spec 23.401
Neither the EPC nor the E-UTRAN supports any explicit feedback to trigger a rate adaptation scheme at the application / service / transport layer.
The MBR of a particular GBR bearer shall be set equal to the GBR.
NOTE: Support for "MBR > GBR" bearers may be introduced in a future release.
The EPC does not support E-UTRAN-initiated "QoS re-negotiation". That is, the EPC does not support an eNodeB initiated bearer modification procedure. If an eNodeB can no longer sustain the GBR of an active GBR bearer then the eNodeB should simply trigger a deactivation of that bearer.

* QCI (QOS Class Indicator)
QCI which is used as a reference to a set of Access Network related
Quality of Service (QoS) parameters, for the transmission between the terminal and the eNodeB.
The purpose of the QCI, and associated parameters, is to provide a representation of QoS parameters to be shared between Core and Access parts of the network.