Introduction:
QoS allow the mobile operator to enable the privileged treatment and priorities for certain users by the service differentiation.
LTE bearers:
We have two main types of bearer (logical path) in LTE the first one is Default Bearer its given for the UE once he attach to the network for regular network use, the second type is Dedicated Bearer its provided to the UE for specific applications and based on data rates we can specify two bearers types:
-
GBR (Guaranteed Bit Rate):
it requires dedicated resources for the duration of the transmission and high data rate used for the application which requires high data rates and low latency.
-
Non-GBR (Non-Guaranteed Bit Rate):
for this bearer the network can't guarantee the availability of the resources during the transmission.
LTE QoS parameters:
QCI (Quality of Service Class Identifier):
Each QCI is defined by priority rate level, packet delay budget and acceptable packet loss
-
ARP (Allocation Retention Priority):
this method is used to decide whether new bearer modification or establishment request should be accepted considering the current resource situation
-
MBR (Maximum bit rate):
parameter used to specify the maximum bit rate supported by a bearer for UL and DL.
-
GBR (Guaranteed bit rate):
Parameter used to specify the minimum guaranteed bit rate supported by a bearer for UL and DL.
-
APN-AMBR (APN Aggregate Maximum Bit Rate):
defines the total bit rate that is allowed to be used for all non-GBR bearers associated with a specific APN.
-
UE-AMBR (APN Aggregate Maximum Bit Rate):
defines the total bit rate allowed to be consumed for all non-GBR bearers of a UE.
in the above figure we can notice the different bearers for one UE and all related parameters as an example.
Bearer QoS Provisioning:
when the default bearer is activated, an MME downloads the QoS profile for the bearer from the HSS and sends it to EPS entities appropriately those parameters can be modified by the Policy and Charging Rules Function (PCRF).
QoS parameters applied to a dedicated bearer are provisioned by PCRF.
The PCRF determines QoS parameters for the bearer based on the
subscription information it received from Subscriber Profile Repository
(SPR) when the bearer is activated.
Sources:
September 11, 2013 | Netmanias (LTE QoS)
October 2013 | Alessandro Vizzarri (Review of studies on end-to-end QoS in LTE networks)
