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360 SIGNALING IN CELLULAR MOBILE TELECOMMUNICATIONScapability indicator (MPCI) to 01. Messages with this MPCI can include words thatare not used in AMPS.12.6.5 Order QualifiersIn AMPS call-control messages, the ORD field identifies an order (or the acknowledgmentof an order), and the ORDQ field qualifies the order—see Figs. 12.4-2through 12.4-5. In IS-54 messages on the FOCC (forward) and RECC (reverse)control channels, the order is qualified by the contents of ORDQ in combinationwith the contents of a five-bit MSG TYP field.In FOCC messages, MSG TYP occupies five bits in the RSVD field of word 2(Fig. 12.4-2). In RECC messages, MSG TYP is in the five-bit RSVD field ofword 2 (Fig. 12.4-3).12.6.6 Assignment of Digital Traffic ChannelsWhen setting up a connection, the MSC needs to assign a channel of a type that iscompatible with the types of available channels in the cell, and with the channeltypes that can be handled by the mobile.When an IS-54 mobile originates a call, the ORDQ and MSG TYP fields in itsorigination message indicate, among other things, whether the mobile can handleanalog voice channels, and/or full-rate, and/or half-rate digital traffic channels.The MSC uses this information to allocate a channel of the proper type.When paging an IS-54 mobile, the MSC uses the ORDQ and MSG TYP fields inits paging message to indicate the types of available channels. The mobile includesthe channel types it can handle in its page response message, and MSC then selects achannel of a compatible type.To conclude this section, we examine a number of IS-54 features and themessages and parameters that support them.12.6.7 AuthenticationThis feature is a defense against the cloning of mobiles (Section 12.5.7). It is basedon the CAVE (cellular authentication and voice encryption) algorithm, which producesan 18-bit result AUTHR (authentication response), from the values of fourinputs:InputAcronymLength(bits)1 Random number generated by MSC RAND 322a In registrations and page responses: the first MIN1 24part of the mobile identification number2b In originations: the last six digits of the6DIG 24called number (BCD coded)3 Mobile serial number MSN 324 Shared secret data for authentication SSD_A 64