TETRA: What is Multi Slot and Dynamic Packet Data?


Multi Slot Packet Data (MSPD) is a TETRA feature that tncreases data throughput for radio users, allowing the radio to use up to 4 timeslots. This would be useful in situations where a User needs to get important data sent but Short Data is (limited size) is inappropriate.

MSPD is the method to get more data sent, using the exisiting TETRA infrastructre. and is useful when used together with WAP & WAPPush.
All TETRA radios are capable of  supporting MSPD and will allow the connection of external data devices such as ANPR cameras; fingerprint readers or computers.

MSPD is only supported on a 2 or more BR site. It also means that additional channels may be
required to balance voice and data traffic channels.

This feature is different from Dynamic Packet Data in that MSPD will use dedicated data channels.

To enable MSPD, the feature flag in the CPS needs to be selected. No other configuration is required within the radio as this setting means that the radio becomes capable of handling MSPD traffic when needed.
The network however has to be configured to support MSPD, and traffic channels allocated for this purpose. There are a number of network based parameters that have to be configured to support this feature.

MSPD is managed from within the Dimetra Network, but many 3rd party applications are able to access this via an API.

It is also possible to share channels between voice and data traffic. These shared channels are known as Dynamic Packet Data Channels (a.k.a. Semi-static PDCH) and are normally dedicated for the DIMETRA Packet Data Service, but they can be preempted by Emergency Calls or Preemptive Priority Calls.

Dynamic Packet Data Channels are particularly useful as they efficiently use traffic resources for smaller systems; systems with a relatively light requirement for packet data, or where the packet data requirement fluctuates with time.

Both PDCH and MSPD offer data speeds that are comparatively slow by modern (post-3G) standards. TETRA only supports 7,2 kbps per timeslot, (3,5kbps with overhead).
To get faster speeds, a TEDS network is needed though this can only do up to 115,2 kbps (or 691,2 kbps if 150 kHz channel spacing is used) and may require new hardware.

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