TTI Mode Configuration

TTI Mode Configuration

Last updated: September 1, 2009

This section is applicable to the EGPRS lab application and test application with a required feature license.

The TTI mode controls the data transfer latency of a PDTCH block. The two values that the TTI mode can be set are RTTI (Reduced Transmission Time Interval) and BTTI (Basic Transmission Time Interval). The data transfer latency is halved to approximately 10ms when using RTTI mode compared with BTTI. In RTTI mode, you can also select the USF mode and coding scheme to be used for control messaging.


In the EGPRS system before Release 7 of the 3GPP standards, the data transfer latency is referred to as transmission time interval (TTI), which is classified as the Basic Transmission Time Interval (BTTI). With BTTI-based transfer, a PDTCH block in the PDTCH multiframe is transmitted across 4 consecutive frames on a single PDTCH physical channel as shown in the figure below.

Since a frame is approximately 4.615ms, the 4 frames gives a TTI of 20ms in a given direction of transfer.


Release 7 of the 3GPP standards introduces the capability to reduce the TTI on EGPRS connections by pairing two PDTCH physical channels on different timeslots for data transfer. Usually the pairing timeslots have all frequency characterization in common. In this configuration, defined as Reduced TTI (RTTI), a PDTCH block interleaved over 4 bursts is transmitted on both PDTCHs in the PDTCH-pair across 2 frames as shown in the figure below. Since the number of frames required for transmission has halved, the TTI is halved to approximately 10ms.

The PDTCH timeslots are grouped into pairs for TBF transfer when the TTI mode is configured to RTTI. Furthermore the TTI mode of the downlink and uplink TBFs must be the same. Therefore only multislot configurations with both an even number of downlink and uplink timeslots shall be valid for RTTI mode.

The TTI mode remains BTTI if an attempt is made to change the TTI mode to RTTI when an invalid multislot configuration is configured. Conversely, if an attempt is made to set an invalid multislot configuration when the TTI mode is currently set to RTTI, the new multislot configuration is applied while the TTI mode shall be forced to BTTI.


The USF Mode is signaled to the mobile station during Packet Uplink Assignment/Reassignment process. The two USF modes that can be selected for an RTTI configuration are BTTI USF mode and RTTI USF mode.

Configurable Parameters

How to set the TTI mode?

The following procedure details how to access and configure the TTI mode.

  1. Press CALL SETUP .
  2. Press PDTCH parms ( F9 ).
  3. Press the More key on the lower right corner to display the PDTCH parms (3 of 3).
  4. Press TTI Mode ( F7 ). Use the knob to select the TTI mode that you want.

The following procedure details how to access and configure the RTTI USF mode parameter.

  1. Press CALL SETUP .
  2. Press the More key on the lower left corner to display the Control menu (2 of 3).
  3. Press the Protocol Control softkey ( F4 ) to display a list of protocol layers.
  4. Press the RLC/MAC softkey ( F2 ).
  5. Press the MAC control softkey ( F2 ), use the knob to highlight and set the RTTI USF mode.

Operating Considerations

The RTTI configuration is only applicable in Active Cell (EGPRS), EGPRS BCH+PDTCH and EGPRS BCH+TCH+PDTCH operating mode. However, parameters associated with RTTI can be changed in other operating modes, but do not effect the test set's operation until the operating mode is changed to the above values.

When the TTI mode is set to RTTI, performing the following measurements will result in the measurement returning an `Unsupported Configuration' integrity indicator value.

Related Topics

Downlink Dual Carrier