codecs which were designed by Digital Voice Systems, Inc. to encode/decode the analog audio signals. It is rumored that the licensing cost for the voice-codecs that are used in P25 standard devices is the main reason that the cost of P25 compatible devices is so high. P25 may be used in "talk around" mode without any intervening equipment between two radios, in conventional mode where two radios communicate through a repeater or base station without trunking or in a trunked mode where traffic is automatically assigned to one or more voice channels by a Repeater or Base Station. The protocol supports the use of Data Encryption Standard (DES) encryption (56 bit), 2-key Triple-DES encryption, three-key Triple-DES encryption, Advanced Encryption Standard (AES) encryption at up to 256 bits keylength, RC4 (40 bits, sold by Motorola as Advanced Digital Privacy), or no encryption. The protocol also supports the ACCORDION 1.3, BATON, Firefly, MAYFLY and SAVILLE Type 1 ciphers. P25 open interfaces P25's Suite of Standards specify eight open interfaces between the various components of a land mobile radio system. These interfaces are: Common Air Interface (CAI) – standard specifies the type and content of signals transmitted by compliant radios. One radio using CAI should be able to communicate with any other CAI radio, regardless of manufacturer Subscriber Data Peripheral Interface – standard specifies the port through which mobiles and portables can connect to laptops or data networks Fixed Station Interface – standard specifies a set of mandatory messages supporting digital voice, data, encryption and telephone interconnect necessary for communication between a Fixed Station and P25 RF Subsystem Console Subsystem Interface – standard specifies the basic messaging to interface a console subsystem to a P25 RF Subsystem Network Management Interface – standard specifies a single network management scheme which will allow all network elements of the RF subsystem to be managed Data Network Interface – standard specifies the RF Subsystem's connections to computers, data networks, or external data sources Telephone Interconnect Interface – standard specifies the interface to Public Switched Telephone Network (PSTN) supporting both analog and ISDN telephone interfaces. Inter RF Subsystem Interface (ISSI) – standard specifies the interface between RF subsystems which will allow them to be connected into wide area networks P25 phases P25-compliant technology has been deployed over two main phases with future phases yet to be finalized. Phase 1 Phase 1 radio systems operate in 12.5 kHz digital