LTE - DATA BEARERS
We all know the Default & dedicated bearers established in LTE. Do we know how many such bearers can be established???
Any works only in NAS will say 2 to 11, based on the EPS bearer Identity. If we dig deep across the following specs of NAS, RRC, MAC & UE conformance, we can come to a conclusion that only 8 bearers are successfully established at a time for a UE.
Funda behind the Bearers:
NAS identifies the Bearers based on the EPS - bearer identity which has a range from 0 to 15
In that 0 to 4 are reserved, so 5 to 15 are used for EBI allocation for every bearer that is created.
This counts to 11 from EPC perspective.
From the RRC spec, 36.331 rel 12.3, MaxDRB's per UE = 11
From the RRC spec, 36.331 rel 12.3, LogicalChannelIdentity for DRB = 3 to 10 (Integer values)
Each Bearer will be mapped from NAS/RRC/MAC as EBI/DRB/LCID
Since the LCID in MAC is having the range from 3 to 10, only 8 DRB's can be established per UE @ a time in LTE. So the Limitation comes in the Logical Channel Identity mapping for the data bearers.
From 36.508, DRB configuration is as follows:
If EBI = X + 4;
Then
DRB ID = X && LCID = X + 2;
Since we have already seen that the Logical Channel Identity range is from 3 to 10, LTE cannot have more than 8 bearers @ a time as of now till Rel 12.3
Hope this helps in better understanding.
We all know the Default & dedicated bearers established in LTE. Do we know how many such bearers can be established???
Any works only in NAS will say 2 to 11, based on the EPS bearer Identity. If we dig deep across the following specs of NAS, RRC, MAC & UE conformance, we can come to a conclusion that only 8 bearers are successfully established at a time for a UE.
Funda behind the Bearers:
NAS identifies the Bearers based on the EPS - bearer identity which has a range from 0 to 15
In that 0 to 4 are reserved, so 5 to 15 are used for EBI allocation for every bearer that is created.
This counts to 11 from EPC perspective.
From the RRC spec, 36.331 rel 12.3, MaxDRB's per UE = 11
From the RRC spec, 36.331 rel 12.3, LogicalChannelIdentity for DRB = 3 to 10 (Integer values)
Each Bearer will be mapped from NAS/RRC/MAC as EBI/DRB/LCID
Since the LCID in MAC is having the range from 3 to 10, only 8 DRB's can be established per UE @ a time in LTE. So the Limitation comes in the Logical Channel Identity mapping for the data bearers.
From 36.508, DRB configuration is as follows:
If EBI = X + 4;
Then
DRB ID = X && LCID = X + 2;
Since we have already seen that the Logical Channel Identity range is from 3 to 10, LTE cannot have more than 8 bearers @ a time as of now till Rel 12.3
Hope this helps in better understanding.
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