DATA TRANSMISSION INTERFACE (DTI)

This section gives a brief introduction to the data handling capabilities of GSM systems. For a more detailed survey of such functions, please refer to the appendix titled “Data Services”.

DTI FUNCTIONS

The DTI implements the GSM Inter-Working Function (IWF). It performs data handling functions such as data rate conversion and provides the functions necessary for data interworking between GSM networks and other networks, including:

• Data Traffic to/from PSTN:

This involves modem and fax calls. For connections to the PSTN a modem is selected by the DTI to perform the necessary rate and format conversions.

• Data Traffic to/from ISDN:

 The whole set of data communications towards ISDN is available, since the MSC/DTI is capable of signaling and mapping basic service information between the ISDN and the GSM network.

• Data Traffic to/from PDNs:

 The DTI handles data traffic to and from Public Data Networks (PDNs) such as the Packet Switched PDN (PSPDN) and Circuit Switched PDN (CSPDN).

• Data Traffic between mobiles:

The data traffic inside the PLMN must pass through the DTI to handle the protocol used for rate adaptation in the radio path.

• HSCSD:

This version of High Speed Circuit Switched Data (HSCSD) allows the connection of 2, 3, or 4 time slots on one radio channel each carrying 9.6 kbits/s. The DTI handles rate conversion to PSTN or ISDN as appropriate.

DTI IMPLEMENTATION

The DTI is integrated within an MSC/VLR. The DTI is managed by the Data Transmission Subsystem (DTS). The DTI sub-rack contains eight plug-in units, each one supporting four data channels. Therefore, each DTI sub-rack can support a total of 32 simultaneous data calls.