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:
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 |
|---|---|
| 2.2k DCCH | |
| 3.4k DCCH | |
| 13.6k DCCH | 144 bits |
| RAB | DCCH RLC Block Size |
|---|---|
|
All RMCs (Reference Measurement Channels) |
|
|
All PS Data RABs (Radio Access Bearers) |
|
|
All CS RABs |
144 bits |
|
All AMR Radio Access Bearers |
144 bits |
If your UE supports changing RLC block size during connection setup, but does not support the RLC Re-establishment procedure, you must either use an SRB that matches your desired service as explained above, or set
RLC Reestablish
to
Off
.
To set the channelization code for the signalling radio bearers, see Downlink Channel Codes .
Manual operation: Select
SRB Parameters
(
F12
on
Call Parms 2 of 3
).
Some UEs can only move to an RMC at the RB Setup phase of the connection if they were assigned to a 2.2k DCCH SRB (i.e. some UEs do not support changing the DCCH RLC block size during connection setup). These same UEs would require a 3.4k DCCH SRB be assigned before establishing any other service type, such as AMR Radio Access Bearer, CS data or PS data. The
SRB Configuration Control
=
Auto
setting can be used to automatically change which SRB the UE is assigned based on the anticipated service.
If
SRB Configuration Control
is set to
Auto
, the test set assigns the UE to a 2.2k DCCH SRB if call status is
Paging
and
Paging Service Type
is set to
RB Test Mode
. Otherwise, the test set assigns the UE to a 3.4k SRB.
If
SRB Configuration Control
is set to
Manual
, the test set assigns the UE to the SRB specified by the
Manual SRB Configuration
setting.
Note, if your UE does not support changing RLC block size during connection setup and you wish to establish a
64k UL / 384k DL RMC (3GPP TS 25.101 A.2.2 and A.3.4)
connection, you must set
SRB Configuration Control
to
Manual
and set
Manual SRB Configuration
to
2.2k DCCH
. The
Auto
setting for
SRB Configuration Control
does not account for this particular channel configuration.
GPIB command: CALL[:CELL]:SRBearer:CCHannel:DEDicated:DRATe[:MANual]
When
SRB Configuration Control
is set to
Manual
, this parameter determines what SRB the test set establishes with the UE.
GPIB command: CALL[:CELL]:SRBearer:CCHannel:DEDicated:DRATe[:MANual]