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Hawaii Preliminary Technical Assessment /CTAP-HUHA-PREASSESS001-RO • To improve radio spectrum effciency • To focus equipment and capabilities on public safety needs • To leverage an open architecture to promote competition across LMR vendors The P25 architecture is composed of an RF subsystem and eight open intertaces to the RF subsystem: RF Subsystem (RFSS) -This is the core of a P25 LMR system that supports all radio functionality. Each vendor is at liberty to design its own proprietary RFSS, but to be P25 compliant it must adhere to the P25 intertace standards outlined below, especially the Common Air Interface. Common Air Intertace (CAI) -CAI is the most recognized element of P25. It ensures that any manufacturer's P25 radio can communicate with any other manufacturer's P25 radio. It defines the . over-the-air communication method: bit rate, bandwidth, and channel access methodologies, as well as modulation scheme, error correction, encryption, identification, signaling, and vocoder. Inter-RF Subsystem Interface (ISSI) -The P25 ISSI provides the messaging structure between multiple trunked systems, allowing them to be connected into wide area networks. A standardized ISSI allows users to communicate between multiple LMR systems without the use of traditional gateways, as long as each Radio Frequency Sub-System (RFSS) supports the ISSI specification. Fixed Station Intertace (FSI) -The FSI connects conventional (not trunked) base stations to a system using a standard interface. For example, an (CALL, ITAC, or VHF base station could be connected to the system using the FSI so that it is accessible by both dispatchers and users in the field. The FSI is defined for both analog and P25 (digital) base stations. The analog interface is identical to analog intertaces that have been used for years by the LMR industry, so that portion of the standard is not new. Now the intertace is standardized and defined in a document. The interface to conventional P25 base stations is new. The intertace between a P25 trunked base station and its controller has not been standardized to date in the P25 standards. Combining trunked base stations from different P25 manufacturers is currently not feasible within a single P25 trunked system. Console Subsystem Interface (CSSI) -The trunked CSSI allows consoles from Manufacturer A to be connected into Manufacturer B's system. Having this intertace would give communication system administrators some flexibility in choosing consoles in the future. It should be noted that the trunked CSSI is based upon and defined as an addendum to the ISSI standard. Therefore, the deployment of this intertace may also require an ISSI capable system. The trunked CSSI may not offer the same feature set that is available from a manufacturer who uses a proprietary interface to connect with Manufacturer B's system. Network Management Interface (NMI) -This element of P25 is under development. It specifies a common management scheme whereby remote users can manage all network elements associated with the RFSS. Fixed Host Data Interface -This element of P25 defines the system's connectivity to computers, data networks, and external data sources at the fixed end of the system, the RFSS. Telephone Interconnect Intertace (TII) -This element of P25 defines the RFSS intertace to the Public Switched Telephone Network (PSTN), supporting both analog and ISDN connections. For example, it enables P25 LMR users to place calls to public land lines. Mobile Data Intertace (MDI) -This P25 element defines the interface through which land mobile subscriber radios can connect to laptops or data networks. 2.5 P25 Subscriber Units There are several vendors who currently manufacture P25 trunked subscriber (portable and vehicular) radios capable of operating in the VHF and 700/800 MHz bands. Several vendors also plan October 2008 10