Test Loopback Mode
For conformance test, we have two major procedure to go through. One is "ACTIVATE TEST MODE" and the other one is "CLOSE UE TEST LOOP". In RF Conformance, only "ACTIVATE TEST MODE" would be enough, but in Protocol Conformance we have to go through both "ACTIVATE TEST MODE" and "CLOSE UE TEST LOOP". (For the details refer to TS 36.509 '5 Test Control (TC) protocol procedures and test loop operation').
Overal function diagram for each test mode from TS 36.509 is as follows.
Message structure of CLOSE UE LOOPBACK is as follows. (For the details refer to TS 36.509 '5 Test Control (TC) protocol procedures and test loop operation').
Let me give you an example for the message to help you understand the message structure.
HEX String : 0F 80 00 03 01 00 01
Analysis Result :
0 : Protocol discriminator
F : Skip indicator
80 : Message type (10000000)
00 : UE test loop mode (000000AB), where A=B=0 when Loopback mode is mode A
03 : Length of UE test loop mode A LB setup list in bytes
01 00 : Uplink PDCP SDU Size = 256 bits
01 : Data Radio Bearer ID = 1