LTE DEDICATED BEARER SETUP

DEDICATED BEARER -

UE should have default bearer before dedicated bearer can be created. However, in case of Piggybacked dedicated bearer, default and dedicated bearers are simultaneously activated
UE can create a max of 11 bearers.1 has to be default, rest can be dedicated
Every APN will have 1 default bearer.

EBI varies from 1 to 9

QCI [Qos Class identifier] range 1 to 9
1-4 : Dedicated bearer
5-9 : Default bearer

Default bearer has MBR[Maximum Bit rate], Dedicated bearer has GBR[Guaranteed bit rate]. MBR = GBR for dedicated bearer


Who initiates it ?
Network initiates it. UE can also do it by sending Bearer resource allocation
Dedicated bearer creation can be initiated by PGW based on local config or based on PCRF

Dedicated bearer can be created in one of the following ways -

1.Piggybacked 

Piggybacked dedicated bearer can be done during attach and additional PDN creation
The outcome of dedicated bearer creation depends on whether default bearer activation was successful or not
The dedicated bearer creation request can be sent to UE along with attach accept/activate default bearer request[during additional PDN conn req]
Multiple dedicated bearer creation request can be sent piggybacked
Request is always piggybacked to response
For ex : Create bearer request is piggybacked to create session response
Modify bearer request is piggybacked to create bearer response
Attach accept is always sent first, before activate dedicated bearer request

2.Non-Piggybacked -

If the request is not sent piggybacked, i.e. if it is sent after attach, before attach complete has been sent, MME shall wait for completion of attach and then send out activate dedicated bearer request.
In other words, it would be like a normal non-piggybacked dedicated bearer creation



Reference :
3gpp  23.401
5.4.1 and Annex F