Signalling Radio Bearer (SRB) Parameters

Last updated: January 15, 2009

A Signalling Radio Bearer (SRB) is a radio bearer that carries DCCH signalling data. An SRB is used during connection establishment to establish the Radio Access Bearers (RABs) and then also to deliver signalling while on the connection (for example, to perform a handover, reconfiguration or release).

The test set supports three SRBs:

• 3.4k DCCH - see 3GPP TS 34.108 6.10.2.4.1.2
•  13.6k DCCH - see 3GPP TS 34.108 6.10.2.4.1.3
•  2.2k DCCH - this signalling radio bearer has the following properties:

2.2k DCCH SRB Properties

Transport Channel Parameters:
TrCH Type	DCH (DCCH)
TB size	100
TF 0	0 x 100
TF 1	1 x 100
TTI (ms)	40
Coding Type	Conv, 1/3
CRC	12 bit
Downlink Physical Channel:
DTX Position	n/a
TFCI	used
Slot Structure	5
SF	256
Uplink Physical Channel:
Min Spreading Factor	256
DPCCH slot format	0
TFCI	used

During connection establishment, an RRC Connection Setup procedure establishes the SRB. The SRB is then used to send all subsequent signalling to start the desired service and establish the radio bearers for the service (see Call Processing Ladder Diagrams). Establishment of the radio bearers is achieved using an RB Setup procedure. The RB Setup procedure configures how both the DCCH and DTCH will be carried on the radio bearers.

The RB Setup may specify a different DCCH RLC block size from the DCCH RLC block size that was being used when only an SRB was present. For example, the DCCH RLC block size for the default 3.4k DCCH SRB is 144 bits, but all RMCs (Reference Measurement Channels) call for a DCCH RLC block size of 96 bits. If the RB Setup specifies a change in the DCCH RLC block size from the stand-alone SRB configuration, the UE and network must change the DCCH RLC block size and then perform an RLC Re-establishment procedure to reset the RLC buffers. If your UE does not support changing the DCCH RLC block size during connection setup, you must establish the call using an SRB with a DCCH RLC block size that is equal to the DCCH RLC block size defined for the service you wish to establish.

SRB DCCH RLC Block Size

SRB	DCCH RLC Block Size
2.2k DCCH	96 bits
3.4k DCCH	144 bits
13.6k DCCH	144 bits

RAB DCCH RLC Block Size

RAB	DCCH RLC Block Size
All RMCs (Reference Measurement Channels) See Radio Bearer Test Mode and Packet Switched Data	96 bits
All PS Data RABs (Radio Access Bearers) See Packet Switched Data	144 bits
All CS RABs See Circuit Switched Data Service	144 bits
All AMR Radio Access Bearers See AMR Setup	144 bits