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Numbers of SRB and DRB in LTE

+1 vote
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Why the numbers of SRB’s and DRB’s are fixed as 3 and 8 in LTE?

posted Aug 11, 2013 by Sanketi Garg

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1 Answer

+2 votes

Regarding the SRB, as far as I can understand it, they may be utilized as follows:
- there is one SRB for common control signalling (refering to CCCH/BCCH), for the initial signaling, when user is not known to the network yet or for broadcast data;
- there is one SRB for dedicated control signalling (refering to DTCH),
- there is one SRB for MBMS channel signaling (refering to MCCH).
So for a single UE there is no need for having more signaling bearers (UE in connected state need to listen to broadcast data, have configured dedicated signaling channel and may have multicast control channel).

answer Aug 11, 2013 by Anderson
@DRB: Its a tradeoff between signaling and variety of types of services (8 DRBs correspond to 3 bits).
commented Sep 16, 2013 by Luv Kumar
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Max. No of DRB in LTE 8 or 11 ?? Also DRB ID vs EPS Bearer ID

Hi All,

It is mentioned in different websites that in LTE max. of 8 DRB can be established per UE. But as per page 652 of 36.331 V13.2.0, the max no. of DRB is 11.
"maxDRB INTEGER ::= 11 -- Maximum number of Data Radio Bearers"

Based on what source are we saying that max. DRB in LTE is 8 and not 11.

It was mentioned in one of the old threads the following:

If EPS bearer ID is = x +4 ;
Then
DRB ID = x;
Logical Channel ID = x + 2

I found the above relationship of DRB ID & EPS Bearer ID to be true for one of the eNB vendors but not for another one.

Example:
EPS ID is 5 and DRB ID is 4 instead of 1. Can somebody comment in this?
NOTE : All these ranges is with respect to DRB establishment

EPS Bearer ID Range is INTEGER (0..15) (But 0-4 is reserved so we use starting from 5 )
DRB ID Range is INTEGER (1..32) (As in LTE max 8 DRB can be established per UE so we use from 1-8)
Logical Channel ID range for DRBs is INTEGER (3..10) ( For for DRB1 we use 3 as logical channed ID)

Thanks

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