Temporary Block Flow (TBF) Parameters

Frame Start Position

The Frame Start Position parameter allows you to specify the type of frame numbering scheme to be used when establishing a data connection.

Changing the frame numbering scheme may enable the test set to establish a data connection with mobile stations which cannot connect under normal conditions.

There are three possible settings:

• Relative: the test set sends the starting frame number to the mobile as a relative offset from the current frame.
• Absolute: the test set sends the starting frame number to the mobile as an absolute frame number.
• Immediate: the test set sends the starting frame number as an immediate assignment.

This parameter is located in the TBF Control parameters menu on the test set's front panel. To access this menu, see How Do I Set the Temporary Block Flow (TBF) Control Parameters? .

If the type of data connection you want to establish is BLER, the commands CALL:FUNCtion:DATA:BLER:LLC:FCSequence and CALL:FUNCtion:DATA:BLER:POLLing:INTerval may also be helpful in enabling the test set to establish a data connection with mobile stations which cannot establish a BLER data connection under normal conditions.

The GPIB command to set the Frame State Position parameter is CALL:FUNCtion:DATA:FRAMe:STARt .

Uplink Data Timeout

The Uplink Data Timeout parameter helps to determine whether the radio link has failed and whether the uplink flow of data messages has been interrupted for an extended period of time.

Note, this parameter only takes effect in the following data connection types: ETSI A, ETSI B (UNACK) and SRB Loopback.

You can turn on or turn off the Uplink Data Timeout timer by setting the Uplink Data Timeout parameter.

• When the Uplink Data Timeout parameter is set to a numeric timeout value, The Uplink Data Timeout timer will run whenever an uplink TBF is active. Each time a valid RLC data block message is received by the RLC/MAC layer the timer is reset to 0, but if the timer expires then the uplink is assumed to have been lost and the connection (uplink and any downlink TBF's) will be released. This timer is to track RLC data message only, reception of RLC control message will not reset the timer.
• When the Uplink Data Timeout parameter is set to OFF, the TBF will not be released.

This parameter is located in the TBF Control parameters menu on the test set's front panel. To access this menu, see How Do I Set the Temporary Block Flow (TBF) Control Parameters? .

You can set the state and duration of the Uplink Data Timeout timer. To set them separately, use CALL:(PDTCH|PDTChannel):TBFLow:UPLink:DLOSt:TIMer:STATe to set the state of the timer, CALL:(PDTCH|PDTChannel):TBFLow:UPLink:DLOSt:TIMer:DURation to set the duration of the timer; use CALL:(PDTCH|PDTChannel):TBFLow:UPLink:DLOSt:TIMer[:SDURation] to set the state and duration simultaneously.

Delayed Downlink TBF

A delayed release of the downlink TBF is when the release of the downlink TBF is delayed following the transmission of a final data block, rather than instantly releasing the TBF. A delayed downlink TBF allows re-use of a downlink TBF for subsequent data transfers without the need for TBF re-establishment, thereby reducing the latency involved between downlink transfers.Support for or use of delayed downlink TBF is not advertised to the mobile station in any way, and therefore is not contained in the System Information messages. The mobile station does not require any changes to support delayed downlink TBF operation.

The connection status displays `Transferring' when Dual Transfer Mode (DTM) is not enabled and `Connected/Transfer' when DTM is enabled until the downlink TBF has been released.

You can set the Delayed Downlink TBF state and duration. To set them separately, use CALL:(PDTCH|PDTChannel):TBFLow:DOWNlink:DELayed[:SDURation] to set the Delayed Downlink TBF state, CALL:(PDTCH|PDTChannel):TBFLow:DOWNlink:DELayed:STATe to set the Delayed Downlink TBF duration; use CALL:(PDTCH|PDTChannel):TBFLow:DOWNlink:DELayed:DURation to set the state and duration simultaneously.

For more information about the delayed release of the downlink TBF, refer to 3GPP TS 44.060 Version 6.14 Section 9.3.1a.

Extended Uplink TBF

The Extended Uplink TBF parameter extends the time period before an uplink TBF is released. The TBF is extended for a period of time (set by the network), following the reception of a data block marked with a Countdown Value of zero (CV=0). 3GPP TS 44.060 Version 6.14.0 states, "In the extended uplink TBF mode, the uplink TBF may be maintained during temporary inactive periods, where the mobile station has no RLC information to send." An extended uplink TBF allows the mobile station to reuse the uplink TBF for subsequent data transfers without the need for TBF re-establishment, thereby reducing the latency involved between uplink data transfers.The network's support for extended uplink TBF is broadcasted on the (P)BCCH within a (Packet) System Information message. The mobile station must have explicit support for the extended uplink functionality to operate correctly.

You can set the Extended Uplink TBF state with the GPIB command CALL[:CELL]:TBFLow:UPLink:EXTended[:STATe] , set the Extended Uplink TBF Duration with the GPIB command CALL:(PDTCH|PDTChannel):TBFLow:UPLink:EXTended:DURation , set the Extended Uplink TBF No Data state with the GPIB command CALL[:CELL]:TBFLow:UPLink:EXTended:NOData[:STATe] .

TBF Re-establishment

When the TBF Re-establishment state is set to On, the test set allows the re-establishment of an uplink TBF before the current TBF is released. Therefore, if the mobile station requires a new uplink TBF it does not have to wait for the current TBF to be released before establishing the next uplink TBF. Instead, the mobile station begins requesting a new TBF as soon as the final acknowledgment for the current uplink TBF has been received from the network.

The GPIB command to set the TBF Re-establishment state is CALL:(PDTCH|PDTChannel):TBFLow:REEStablish[:STATe] .

For more information about TBF Re-establishment, refer to 3GPP TS 44.060 Version 6.14.

Packet Uplink Ack/Nack Interval

The Packet Uplink Ack/Nack Interval parameters allows you to specify the number of RLC block periods to wait before the test set sends the Packet Uplink Ack/Nack RLC control message to Mobile Station during an uplink TBF. You can influence the data throughput by setting the parameters. A high Packet Uplink Ack/Nack Interval value which exceeds the size of RLC transmit window may cause the RLC transmit window to stall, a low Packet Uplink Ack/Nack Interval value may prevent downlink data being sent to the MS as RLC control messages have higher priority than RLC data.

For multislot configurations that have fewer downlink timeslots than uplink timeslots, the test set attempts to match the specified Ack/Nack period in a `best effort' manner. If the requested number of Ack/Nack messages would exceed the available downlink bandwidth, the lowest value possible is used instead. For example: For a 1D2U multislot configuration with Packet Uplink Ack/Nack Interval set to "1", the test set's 'best effort' value used is "2".

Just as the test set allows for the RLC transmit "Window Size" parameter to be different for GPRS and EGPRS, it also allows for the Packet Uplink Ack/Nack Interval to be configured individually for GPRS and EGPRS operations. These parameters are:

• Packet Uplink Ack/Nack Interval (GPRS):

  The valid range of this parameter is 1 to 63. The GPIB command to set this parameter is CALL:FUNCtion:DATA:PUPLink:ACKNack:INTerval:GPRS .

• Packet Uplink Ack/Nack Interval (EGPRS):

  The valid range of this parameter is 1 to 1023. The GPIB command to set this parameter is CALL:FUNCtion:DATA:PUPLink:ACKNack:INTerval:EGPRs .

This parameter is located in the TBF Control parameters menu on the test set's front panel. To access this menu, see How Do I Set the Temporary Block Flow (TBF) Control Parameters? .

Final Block Polling

The Final Block Polling parameter allows you to control the uplink data throughput by setting the polling rate.

When a downlink TBF needs to be released (i.e. there is no more data to transfer at the RLC layer), the network will send the last data block with the Final Block Indicator bit set to 1. It will also set the bit or bits required to poll. This will indicate to the DUT that this data block is the last in the TBF and that it should send a Packet Downlink ACK/NACK message so that the TBF can be released according to 3GPP TS 44.060 section 9.3.2.6. These ACK/NACK messages will take transmission priority over data blocks for the DUT and each time it receives a valid poll it must respond with the appropriate message.

There are two possible settings for this parameter:

• Normal: The poll bit is set every time a RLC data block with the Final Block Indicator is set. The DUT will send a control block in the place of a data block when it receive a RLC data block with poll bit set, thus reducing uplink data throughput in the process.
• Reduced: the test set poll twice within each RRBP period, initiated by the FBI being set. The first poll happens on the first instance of the FBI transmission. The second poll happens approximately halfway through the RRBP period. The exact timing of the poll is determined internally in the protocol stack via the frame numbers. An RRBP period is about 100ms, so the uplink data throughput will be increased.

This parameter is located in the TBF Control parameters menu on the test set's front panel. To access this menu, see How Do I Set the Temporary Block Flow (TBF) Control Parameters? .

The GPIB command to set this parameter is CALL:(PDTCH|PDTChannel):TBFLow:DOWNlink:FBIndicator:POLLing .

Early Re-Transmissions

This setting affects the BLER accuracy when the ETSI B Ack Measurement mode of BLER measurement is `Polling' and the packet transfer mode is `Acknowledged'. You can improve the accuracy of BLER measurement by setting the Early Re-Transmission Sate to OFF.

In Acknowledged Packet Transfer mode, the test set assigns the RLC data blocks a specific status value while they reside in the stack awaiting transmission. This status is used to determine which block is transmitted and when the block will be transmitted. The statuses include:

• RECEIVED - new blocks are given this status when they arrive in the stack. These blocks have not yet been transmitted.
• PENDING_ACK - blocks that have just been transmitted are given this status.
• NACKED - blocks that are NACKED by the DUT, i.e. requiring a re-transmission. These will be stored in the stack in a queue until such a time as it can be re-transmitted, then it will be set to pending_ack.
• ACKED - blocks that are acknowledged are given this status. These blocks will normally be deleted immediately after becoming acked.

When the DUT requests a re-transmission of a block it will be marked as NACKED in the stack. If there are no other NACKED blocks in the stack then this block will be re-transmitted before any other blocks, if there are other NACKED blocks already waiting then they will be processed first. After these NACKED blocks are sent their status moves to PENDING_ACK. When the Early Re-transmission State is set to ON, the PENDING_ACK block is selected for transmission if there is no NACKED or RECEIVED block in the stack. This means that a RLC block is sent to the DUT more than one time before the test set know the status of the initial transmission. This will affect the accuracy of BLER results in two ways:

1. The DUT may have more than one attempt to successfully decode a data block.
2. If a RLC block is sent to the DUT more than one time before receiving the Packet Downlink ACK/NACK message and the previous ones were failed to be decoded but the last one passed, then the test set will mark the block as ACKED and will not record any BLER for it.

When the Early Re-transmission State is set to OFF, the test set first determines if it is required to poll the DUT. If the test set determines that a poll is required, it sends the last data block to the DUT that has already been `ACKED'. As the block has already been counted for BLER and as the DUT has already acked it, it is safe to re-transmit it. Note that the test set determines the last `ACKED' data block from the bitmap of the Packet Downlink ACK/NACK message.

This parameter is located in the TBF Control parameters menu on the test set's front panel. To access this menu, see How Do I Set the Temporary Block Flow (TBF) Control Parameters? .

The GPIB command to set this parameter is CALL:(PDTCH|PDTChannel):TBFLow:DOWNlink:RETRansmit[:STATe] .

T3192 TBF Release Timer

See Configurable Timers for more information.

The GPIB command to set the Timer is CALL[:CELL]:TBFLow:T3192 .

ARAC on receipt of PRR

When the ARAC on receipt of PRR parameter is set to ON , the test set sets the ARAC request bit in the PACKET UPLINK ASSIGNMENT message when assigning an EGPRS TBF. The mobile then provides the network with its radio access capabilities for the frequency bands it supports by sending a PRR (PACKET RESOURCE REQUEST) message, and an ADDITIONAL MS RADIO ACCESS CAPABILITIES message if all the requested information does not fit in the PACKET RESOURCE REQUEST.

Currently, setting the ARAC request bit in the PACKET UPLINK ACK/NACK message is not supported by the test set.

The ARAC on receipt of PRR parameter is only available when the operating mode is set to Active Cell (EGPRS) .

The GPIB command to set the ARAC upon PRR State parameter is CALL:(PDTCH|PDTChannel):ARAC:PRRequest[:STATe] .

See 3GPP TS 44.060 section 7.1.2.2.1a and 3GPP TS 44.018 section 3.5.2 for more information about how to request the Additional MS Radio Access Capability information.

Operating Considerations

It is recommended that you should not change the Frame Start Position parameter while the data connection status is Starting , as there is no guarantee whether the new setting or the previous setting will be used for the current data connection.

The delayed downlink TBF, extended uplink TBF, and TBF Re-establishment parameter settings only take affect when the Operating Mode is set to Active Cell (serving cell GSM, GPRS, or EGPRS) and the Data Conn Type is set to Auto .

The Operating Mode must be set to Cell Off when you change the Extended Uplink TBF state. If not, the following error appears on the test set's front panel.

" GSM/GPRS operation rejected; Attempting to set BCH parameter while generating a BCH "

Related Topics

How Do I Set the TBF Parameters?