5.3 UE test loop procedures

34.1093GPPRelease 17Special conformance testing functionsTerminal logical test interfaceTS

5.3.1 General

The UE test loop function is intended for:

– Testing of receiver characteristics based on BER (Bit Error Ratio) measurement. The SS calculates BER from a bit-by-bit comparison of data sent to and received from UE. BER measurement requires symmetric RAB bit-rates.

– Testing of receiver performance based on BLER (BLock Error Ratio) measurement. The SS calculates BLER based on the RLC STATUS SDU received from the UE operating in RLC acknowledged mode; or the SS calculates BLER based on checking returned downlink data and downlink CRC by UE operating in UE test loop mode 2.

– Testing of UE Blind Transport Format Detection.

– Testing of UE transmitter characteristics.

– Testing of UE transmitter DTX characteristics.

– Testing of radio bearers (UE test loop function emulates terminal equipment).

– Counting received RLC SDUs on a given MTCH. This may be used for the estimation of RLC SDU error rate for testing of MTCH performance.

– Generating reliable data transmission flow on E-DPDCH for E-DCH testing (UE test loop mode 1).

– Testing of UE uplink packet filtering (UE test loop mode 4).

5.3.2 Close UE test loop

Figure 5.3.2.1: Close UE test loop procedure

5.3.2.1 General

The SS uses the close UE test loop procedure to start the UE Test Loop function in the UE. A prerequisite for UE test loop mode 1, UE test loop mode 2 and UE test loop mode 4 is that at least one bidirectional user plane radio bearer has been established between SS and UE. A prerequisite for UE test loop mode 3 is that at least one MTCH has been established. See TS 34.108 [10], clause 7 for generic setup procedures.

The UE shall provide for normal Uu layer 1, layer 2 and RRC functionality while the UE test loop function is active. This includes (but is not limited to) handover procedures and normal disconnection of the radio bearer. The loopback shall be maintained across handovers, but after radio bearer disconnection, the loopback shall cease to exist.

5.3.2.2 Initiation

The SS can request the UE to close a test loop in mode 1, mode 2 or mode 4 if at least one bidirectional user plane radio bearer is established and the UE radio bearer test mode is active.

When testing reception of MBMS services not operating in MBSFN mode the SS can request the UE to close the test loop in mode 3 if any MTCH is established and the UE radio bearer test mode is active.

When testing reception of MBMS services operating in MBSFN mode the SS can request the UE to close the test loop in mode 3 before or after any MTCH has been established on the MBSFN carrier and the UE radio bearer test mode is active.

The SS requests the UE to close its radio bearer test loop by transmitting a CLOSE UE TEST LOOP message. The SS then starts timer TT01.

5.3.2.3 Reception of CLOSE UE TEST LOOP message by the UE

If UE test loop mode 1, mode 2 or mode 4 has been selected and no user plane bidirectional radio bearers are established or the UE radio bearer test mode is not active, then the UE shall ignore any CLOSE UE TEST LOOP message.

If UE test loop mode 1, mode 2 or mode 4 has been selected and one or more user plane bidirectional radio bearers are established, the UE shall close the test loop on all user plane bidirectional radio bearers and then send back to the SS a CLOSE UE TEST LOOP COMPLETE message. The loopback shall be operational prior to the sending of the acknowledgement. The UE shall not close the UE test loop mode 1, mode 2 or mode 4 on any unidirectional user plane radio bearers.

If UE test loop mode 3 has been selected and a MTCH corresponding to the specified MBMS short transmission identity is established, the UE shall commence counting of received RLC SDUs on this MTCH. The counter value shall be reset to zero on reception of CLOSE UE TEST LOOP MODE 3 and the UE shall send back a CLOSE UE TEST LOOP COMPLETE message to the SS.

If UE test loop mode 3 has been selected, no MTCH corresponding to the specified MBMS short transmission identity is established and the UE supports MBMS service operating in MBSFN mode, the UE shall wait until a MTCH is established corresponding to this MBMS short transmission identity to close the test loop and commence counting of received RLC SDUs. The counter value shall be reset to zero when the MTCH is established, the test loop shall be closed and the UE shall send back a CLOSE UE TEST LOOP COMPLETE message to the SS.

If the test loop is already closed on one or more user plane radio bearers, the UE shall still respond as if the loop had been open, i.e. the CLOSE UE TEST LOOP COMPLETE message shall be sent.

NOTE: There is no requirement on the UE to read the content of the CLOSE UE TEST LOOP message if it is received while the test loop is closed.

If UE test loop mode 1 has been selected then the loop back scheme according to subclause 5.3.2.6 shall be performed by the UE.

If UE test loop mode 2 has been selected then the loop back scheme according to subclause 5.3.2.7 shall be performed by the UE.

If UE test loop mode 3 has been selected then the RLC SDU counting scheme according to subclause 5.3.2.8a shall be performed by the UE.

If UE test loop mode 4 has been selected then the loop back scheme according to subclause 5.3.2.8b shall be performed by the UE.

5.3.2.4 Reception of CLOSE UE TEST LOOP COMPLETE message by the SS

Upon reception of the CLOSE UE TEST LOOP COMPLETE message the SS stops timer TT01.

5.3.2.5 TT01 timeout

If TT01 expires, then the SS shall indicate this to the test case. The procedure is then completed.

5.3.2.6 UE test loop mode 1 operation

If the configuration of a user plane radio bearer with a closed UE test loop mode 1 includes the PDCP protocol layer, configured by "PDCP info" (see [5]), then the loop back scheme according to subclause 5.3.2.6.1 shall be performed by the UE for that radio bearer.

If the PDCP protocol layer is not used for a user plane radio bearer with a closed UE test loop mode 1 then the loop back scheme according to subclause 5.3.2.6.2 shall be performed by the UE for that radio bearer.

5.3.2.6.1 Loopback of PDCP SDUs

If UE test loop mode 1 has been closed on a user plane radio bearer and the setup of that radio bearer includes configuration of PDCP protocol layer, configured by "PDCP info" (see [5]), then the following loop back scheme shall be performed by the UE.

After the UE has closed UE test loop mode 1 on a user plane radio bearer, every PDCP SDU received by the UE on that radio bearer (downlink) shall be taken from the output of the PDCP service access point (SAP) and be input to the correspondent PDCP SAP and transmitted (uplink).

The UE shall provide for normal PDCP operation.

The PDCP loopback operation is illustrated in figure 5.3.2.6.1.1.

Figure 5.3.2.6.1.1: Loop back of PDCP SDU
(DL RLC SDU size = UL RLC SDU size = N)

5.3.2.6.2 Loopback of RLC SDUs

If UE test loop mode 1 has been closed on a user plane radio bearer and the setup of that radio bearer does not include configuration of the PDCP protocol layer ("PDCP info" is not configured (see [5]) then the following loop back scheme shall be performed by the UE.

After the UE has closed UE test loop mode 1 on a user plane radio bearer, every user data block received by the UE on that radio bearer (downlink) shall be taken from the output of the RLC service access point (SAP) and be input to the correspondent RLC SAP and transmitted (uplink). The UE reads the UL RLC SDU size parameter from the "LB Setup RB IE#k" parameter associated with that radio bearer, see subclause 6.2.

If no "LB Setup RB IE#k" parameter is associated with that radio bearer then the UE shall use the same UL RLC SDU size as the received DL RLC SDU.

For the case when the "UL RLC SDU size" parameter is set to "0" no data shall be returned.

For the case when the "UL RLC SDU size" parameter is set to the same value as the down link (DL) RLC SDU block size then the complete user data block shall be returned, see figure 5.3.2.6.2.1.

Figure 5.3.2.6.2.1: DL and UL RLC SDU block size equal
(DL RLC SDU size = UL RLC SDU size = N)

For the case when the "UL RLC SDU size" parameter is set to a value less than the down link (DL) RLC SDU block size then the UE shall return the first K bits of the received block, where K is the UL block size, see figure 5.3.2.6.2.2.

Figure 5.3.2.6.2.2: DL > UL RLC SDU block size
(DL RLC SDU size = N, UL RLC SDU size = K)

For the case when the "UL RLC SDU size" parameter is set to a value bigger than the down link (DL) RLC SDU block size then the UE shall pad the UL send block by repeating the received data block until the UL send block has been filled (truncating the last block if necessary), see figure 5.3.2.6.2.3.

Figure 5.3.2.6.2.3: DL < UL RLC SDU block size
(DL RLC SDU size = N, UL RLC SDU size = 2*N + K)

For the case of loopback of data from DL HS-DSCH to UL E-DPDCH the following applies:

– For RLC unacknowledged mode, when the UL RLC SDU block does not fit in the Transmission buffer, the UE shall discard the UL RLC SDU block. The UE shall perform the discard either by the loopback entity or by the UM RLC entity as described in [19] subclause 9.7.3.5.

– For RLC unacknowledged mode the minimum total RLC UM buffer size supported by the UE shall be [10 kbytes]. See note 2.

NOTE 1: The minimum total RLC UM buffer size and the RLC SDU discard functionality has been specified to enable E-DCH RF performance testing.

NOTE 2: The value for minimum total RLC UM buffer size is preliminary set to 10kByte. The value is for further study to secure that the required buffer size is enough to cover all E-DCH RF testing scenarios and UE E-DCH categories.

5.3.2.7 UE test loop mode 2 operation

For UE test loop mode 2 to work correctly ciphering shall be disabled.

For the UE to be able to return downlink transport block data and CRC bits then the up link transport channel configuration shall include a transport format for which the block size is equal to or bigger than the sum of the downlink transport block size and the number of downlink CRC bits. If no such uplink transport format exists then the returned data and CRC bits will be truncated.

5.3.2.7.1 Loopback of downlink transport block data and downlink CRC

If UE test loop mode 2 has been closed on a user plane radio bearer then the following loop back scheme shall be performed by the UE for all transport channels associated with a single DTCH:

After the UE has closed test loop mode 2 on a user plane radio bearer then the UE shall copy the downlink transport block and CRC bits received on that radio bearer to the uplink transport block and transmit in the up link transport channel configured for that radio bearer.

If the uplink configuration for that radio bearer is of variable rate then the transport format with the smallest transport block size which fits the downlink transport block size and the downlink CRC bits shall be selected for the uplink. In case there is no uplink transport format that fits the downlink transport block data and the downlink CRC bits then the data and CRC bits shall be truncated using the transport format with the biggest transport block size configured for that uplink transport channel.

UE test loop mode 2 operation is illustrated for the case when the uplink transport block size is bigger than the sum of the downlink transport block size and size of downlink CRC in figure 5.3.2.7.1.

UE test mode 2 operation is illustrated for the case when uplink transport block size is smaller than the sum of downlink transport block size and size of downlink CRC in figure 5.3.2.7.2.

Figure 5.3.2.7.1. UE test loop mode 2 operation for the case when uplink transport block size
is bigger than the sum of downlink transport block size and size of downlink CRC

Figure 5.3.2.7.2. UE test loop mode 2 operation for the case when uplink transport block
does not fit downlink transport block and downlink CRC bits.

5.3.2.8 Void

5.3.2.8a UE Test Loop Mode 3 Operation

In UE test loop mode 3, the UE is required to count RLC SDUs received on a given MTCH, which must have been configured in the UE prior to closing UE test loop mode 3.

When the CLOSE UE TEST LOOP message is received by the UE, the counter value is reset to zero. After this, every user data block successfully received by the UE on the chosen MTCH shall cause the counter value to be incremented by one. A 32 bit counter shall be used and the UE counter value is undefined if more than 4294967295 RLC SDUs have been received by the UE.

Figure 5.3.2.8a.1: UE test loop mode 3 operation

5.3.2.8b UE test loop mode 4 operation

If the configuration of a user plane radio bearer with a closed UE test loop mode 4 includes the PDCP protocol layer, configured by "PDCP info" (see [5]), then the loop back scheme according to subclause 5.3.2.8b.1 shall be performed by the UE for that radio bearer.

If the PDCP protocol layer is not used for a user plane radio bearer with a closed UE test loop mode 4 then the UE behaviour is unspecified.

5.3.2.8b.1 Loopback of IP PDUs

If UE test loop mode 4 has been closed on a user plane radio bearer and the setup of that radio bearer includes configuration of PDCP protocol layer, configured by "PDCP info" (see [5]), then the following loop back scheme shall be performed by the UE.

After the UE has closed UE test loop mode 4 on a user plane radio bearer, every IP PDU (=PDCP SDU) received by the UE in downlink shall be taken from the output of the PDCP service access point (SAP) and be input to the SAP of the UL TFT handling function and transmitted in uplink.

The UE shall provide for normal PDCP operation and uplink packet filtering operation based on received UL TFT.

The IP PDU loopback operation is illustrated in figure 5.1.4 and 5.3.2.8b.1.1.

Figure 5.3.2.8b.1.1: Loop back of IP PDU
(DL IP PDU size = UL IP PDU size = N)

5.3.2.9 Loopback delay requirement

5.3.2.9.1 General loopback delay requirement

Loopback delay is specified as delay between received DL radio frames and their corresponding UL radio frames produced from the received data. The loopback delay is measured at the antenna connector of the UE and specified in the unit of radio frame(s). Timing offset between DL and UL radio frames, and timing errors are not included in the loopback delay.

For UE operating in UE test loop mode 1 the loopback delay requirement is applicable for a radio bearer with a closed test loop if the MAC and RLC protocols for that radio bearer are configured for transparent operation and if the downlink RLC SDU size is equal to the downlink transport block size, i.e. no segmentation/concatenation takes place.

For UE operating in UE test loop mode 1 the loopback delay requirement is not applicable for unacknowledged mode radio bearers configured on HS-DSCH and E-DPDCH.

NOTE 0: UE test loop mode 1 is used for E-DCH RF performance testing. For these test cases unacknowledged mode radio bearer configurations for HS-DSCH and E-DPDCH are used. This means that the data rate may vary depending on absolute and relative grants given by the SS. In addition overflow of UE UM buffer may happen as SS needs to guarantee continous data in uplink..

For UE operating in UE test loop mode 2 the loopback delay requirement is applicable for any radio bearer configuration.

For UE operating in UE test loop mode 3, the received data is only counted, and is not looped back to the SS so the loopback delay requirement is not applicable.

The UE shall maintain a fixed loopback delay (the loopback delay shall not vary during a test) if the configuration of radio bearers with closed test loops remains unchanged. The loopback delay shall not exceed the number of radio frames correspondent to 10 times the TTI of the actual transport channel configuration.

The loopback delay requirement for the 10ms TTI case is illustrated in figure 5.3.2.9.1.

NOTE 1: See TS 25.211 [11], subclause 7.6.3 for definition of the timing offset between DL and UL radio frames for FDD mode.

NOTE 2: See TS 25.133 [12], subclause 7.1 for definition of the timing error for FDD mode.

Figure 5.3.2.9.1: Loopback delay requirement (TTI=10 ms)

5.3.2.9.2 Loopback delay requirement for RLC and PDCP SDUs (UE Test loop mode 1)

The maximum delay from receiving an RLC or PDCP SDU in a downlink SAP until returning an SDU in the correspondent uplink SAP shall be within the delay requirement specified in subclause 5.3.2.9.1.

The UE test loop function, operating in UE test loop mode 1, shall for every radio bearer with a closed test loop be able to return at least 4 SDUs within the time equal to the TTI of the actual radio bearer.

NOTE: To enable testing of the Conversational CS TM reference radio bearer combinations as specified in 34.108 subclause 6.10 a UE must be able to loop back 4 SDUs per TTI. E.g. for "Conversational / unknown / UL:64 DL:64 kbps / CS RAB" operated in TM RLC mode 4 SDUs are needed to fill the transport format existing of 4×640 bits.

NOTE: The loopback delay requirement in 5.3.2.9.2 does not impose any synchronisation mechanisms between the uplink RLC entity and the UE test loop function. Thus it could happen that a UE when having received 4 SDUs within one and the same TTI may deliver the SDUs to the uplink RLC entity in two subsequent TTIs. For a TM radio bearer requiring multiple SDUs to fill a transport block set then "Timer discard without explicit signalling" needs to be configured to secure that the TM RLC entity does not discard the SDUs in case they are delivered in subsequent TTIs.

5.3.3 Open UE test loop

Figure 5.3.3.1: Open UE test loop procedure

5.3.3.1 General

The SS uses the procedure open UE test loop to deactivate the UE test loop function in the UE.

5.3.3.2 Initiation

The SS requests the UE to open all closed radio bearer test loops by transmitting an OPEN_UE_TEST _LOOP_CMD message. The SS then starts timer TT01.

5.3.3.3 Reception of OPEN UE TEST LOOP message by the UE

If no bidirectional user plane radio bearers are established in UE Test loop mode 1 or UE test loop mode 2, the UE shall ignore any OPEN UE TEST LOOP message.

If one or more user plane radio bearer test loops are closed, the UE shall open all test loops and send back to the SS an OPEN UE TEST LOOP COMPLETE message.

If the test loops are already open, the UE shall still respond as if the loops had been closed, i.e. the OPEN UE TEST LOOP COMPLETE message should be sent prior to TT01 expiring.

5.3.3.4 Reception of OPEN UE TEST LOOP COMPLETE by the SS

Upon reception of the OPEN UE TEST LOOP COMPLETE message the SS stops timer TT01.

5.3.3.5 TT01 timeout

If TT01 expires, then the SS shall indicate this to the test case. The procedure is then completed.