P25 Trunked Systems

The promise of open standards for Public Safety Trunked radio systems has come to fruition with Scout’s support for the P25 CSSI interface, now available in Scout V1.10. This software based redundant IP interface joins the P25 DFSI as well as conventional radio interfaces and support for multiple wire-line commercial trunked radio systems available in Scout’s VPGate.

P25 CSSI is a VoIP connection between the console subsystem and the P25 RF Subsystem (RFSS) utilizing SIP-based messaging. P25 CSSI is a published standard and defined in Addendum 2 of the Telecommunications Industry Association (TIA) Standard Ã’P25 CSSI, TIA-102.BACAÓ. Most radio manufacturers are migrating support from proprietary interfaces to the P25 CSSI standard, however it’s important to note there are also valuable proprietary features that are not supported by the standard (i.e. Failsoft) that will remain available.

The P25 CSSI interface, like P25 DFSI, conveys voice using IMBE encoded packets, with or without encryption, from subscriber radio to the console subsystem. Scout uses the latest AMBE+2ª enhanced full rate vocoder with improved forward error correction (FEC) and noise reduction for excellent audio quality. Unlike competitive systems, Scout provides full multi-site redundancy capabilities in the standard P25 console product to ensure that your connection to the radio system is always available. Furthermore, since Scout is a pure end-to-end IP system with redundancy built-in (and not a TDM system with limited IP interfaces), you are assured of scalability and flexibility of deployment to different locations, without duplication of legacy backroom equipment. Although in the real world it may never be needed, Scout can connect to over 100 different P25 RF Subsystems simultaneously!

The Telecommunications Industry Association (TIA) has yet to ratify a standard test suite to measure compliance with the CSSI standard, leaving it to individual manufacturers to self-certify. Avtec has chosen to perform certification testing with market leaders promoting open interfaces in Radio systems, namely Cassidian (EADS) and Tait Radio Communications. Avtec is committed to compliance testing with multiple vendors in the near future as the test standards mature.

Scout P25 Console with P25 RFSS

Scout offers a P25 trunked radio driver for VPGate which enables individual Talk Group and “Unit call resources” to be defined as endpoints in the console subsystem. Unit call resources are connections that look to the P25 RFSS like a radio; they may be used for inbound and outbound calls from/to a specific subscriber unit. These endpoints are assignable to any or all Scout console positions in a system. The connection from VPGate to the P25 RFSS uses standard IP transport; there are no external controllers required.

The Scout P25 Console system V1.10 supports the following P25 trunking system features:

  • DES/AES Encryption enable/disable
  • Unit Check
  • Unit Monitor
  • Unit (Individual) Calls to subscriber unit
  • Unit (Individual) Calls inbound to console subsystem
  • Group Calls
  • ANI with Aliasing
  • Call Alert Inbound and Outbound (to Individual call resource)
  • Emergency Call (Inbound from subscriber)
  • Console Priority
  • PTT
  • Failsoft (EADS proprietary only; not part of CSSI standard)
  • Encryption Key Management

Note: In addition to P25 console specific features, standard console features are fully supported for P25 endpoints, including Patch, Unselect, and Simulselect. For instance, Patch may be used to set up interoperability with other radio bands.

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