5.1 General description

34.1093GPPRelease 17Special conformance testing functionsTerminal logical test interfaceTS

The UE test loop function provides access to isolated functions of the UE via the radio interface without introducing new physical interfaces just for the reason of conformance testing.

NOTE: It should be emphasised that the UE test loop function only describes the functional behaviour of the UE with respect to its external interfaces; physical implementation of the UE test loop function is completely left open to the manufacturer.

The UE test loop function is activated by transmitting the appropriate Test Control (TC) message to the UE, see clause 6.

For the purposes of this specification only, the following definitions are used:

Bidirectional Radio Bearer:

If the "RB mapping info" information element ([5] subclause 10.3.4.21) for the currently active configuration of a radio bearer includes mappings to both uplink and downlink transport channels then this radio bearer is defined to be a bidirectional radio bearer.

Unidirectional Radio Bearer:

If the "RB mapping info" information element ([5] subclause 10.3.4.21) for the currently active configuration of a radio bearer includes mappings to only uplink or downlink transport channels then this radio bearer is defined to be a unidirectional radio bearer.

NOTE: This definition of unidirectional radio bearer is only applicable to RLC Unacknowledged Mode, in this version of the specification.

The UE test loop function can be operated in four different loopback modes:

– UE test loop mode 1;

– UE test loop mode 2;

– UE test loop mode 3; and

– UE test loop mode 4.

UE test loop mode 1, 2 and 4 provide loopback of data for bidirectional radio bearers. UE test loop mode 3 provides counting of successfully received RLC SDUs on a given MTCH.

The UE test loop mode 1 and 2 are mandatory to all UEs. The UE test loop mode 3 is mandatory for UEs supporting MBMS. The UE test loop mode 4 is mandatory for UEs supporting network initiated secondary PDP context.

Support of Update UE Location Information function is optional for the UE.

Figure 5.1.1 shows a functional block diagram of the UE test loop function for UE test loop mode 1.

Figure 5.1.2 shows a functional block diagram of the UE test loop function for UE test loop mode 3 applicable when testing reception of MBMS services not operating in MBSFN mode.

Figure 5.1.3 shows a functional block diagram of UE test loop function for UE test loop mode 3 applicable when testing MBMS services operating in MBSFN mode. Test loop command/response messages are sent on the unicast carrier while the UE test loop mode 3 operates on the MTCH on the MBSFN carrier.

Figure 5.1.4 shows a functional block diagram of UE test loop function for UE test loop mode 4 applicable when testing network initiated secondary PDP context and routing of UE uplink IP packets based on network signalled UL TFT.

For UE test loop mode 1 the loopback point is located above Layer 2. Depending on the actual radio bearer setup loopback is performed of RLC SDUs or PDCP SDUs according to the procedure specified in subclause 5.3.3.2.

For UE test loop mode 3 the UE counts each successfully received RLC SDU on the MTCH configured for RLC SDU counting.

The loop back point for UE test loop mode 1 has been selected above Layer 2 to separate the protocol configurations from the UE test loop function. By configuration of RLC and MAC layers other loop back points may functional be achieved. E.g. by transparent configuration of RLC and MAC layer functional loop back point at Transport channel level can be achieved to implement the reference measurement channels as specified by TS 34.121 [8], Annex C for FDD and by TS 34.122 [9], Annex C for TDD.

For UE test loop mode 2 both data and CRC are looped back. UE test loop mode 2 is intended for Blind Transport Format Detection (BTFD) testing and BLER testing of DL 12.2 kbps reference measurement channel for which loopback of downlink CRC is required. UE test loop mode 2 can also be used for BLER testing of DL 64, 144 and 384 kbps reference measurement channels if the UE supports correspondent UL reference measurement channels. Both received data and CRC bits for the DCH transport channel used for the BTFD test case is returned according to the procedure specified in subclause 5.3.3.3.

The loop back point for UE test loop mode 4 has been selected above UE’s function for UL TFT handling. IP PDUs (=PDCP SDUs) received in downlink are returned to the UL TFT handling SAP in the UE. The UE shall perform normal operation of the UL TFT handling function while UE test loop mode 4 is active, i.e. the UE shall perform routing of uplink IP packets to the uplink radio bearers in accordance with the signalled UL TFT filters as specified in [20] and [2].

A specific radio bearer test mode is specified to be used together with the UE test loop function. The purpose of the radio bearer test mode is to put the UE into a mode where: SS can set up radio bearers to be terminated in the UE test loop function without having to involve CC or SM; and to disable any control mechanisms in NAS protocols or in any UE applications that otherwise could cause the RRC connection to be released.

Figure 5.1.1: UE Test Loop Mode 1 function (TC =Test Control, LB = Loop Back entity)

Figure 5.1.2: UE test loop mode 3 for testing MBMS services not operating in MBSFN mode

Figure 5.1.3: UE test loop mode 3 for testing MBMS services operating in MBSFN mode

Figure 5.1.4: Model for UE Test Loop Mode 4 for testing UE UL TFT handling