4. Symbols and Abbreviations

4.1     Data Units

        TPDU    Transport protocol data unit
        TSDU    Transport service data unit
        NSDU    Network service data unit

4.2     Types of transport protocol data units




        CR TPDU         Connection request TPDU
        CC TPDU         Connection confirm TPDU
        DR TPDU         Disconnect request TPDU
        DC TPDU         Disconnect confirm TPDU
        DT TPDU         Data TPDU
        ED TPDU         Expedited data TPDU
        AK TPDU         Data acknowledge TPDU
        EA TPDU         Expedited acknowledge TPDU
        RJ TPDU         Rejected TPDU
        ERR TPDU        Error TPDU

4.3     TPDU fields

        LI              Length indicator (field)
        CDT             Credit (field)
        TSAP-ID         Transport service access point identifier
                        (field)
        DST-REF         Destination reference (field)
        SCE-REF         Source reference (field)
        EOT             End of TSDU mark
        TPDU-NR         DT TPDU number (field)
        ED-TPDU-NR      ED TPDU number (field)
        YR-TU-NR        Sequence number response (field)

4.4     Parameters

        T (R)           Receive sequence number
        T (S)           Send sequence number

4.5     Timer variables

        T1              Elapse time between retransmissions
        N               The maximum number of retransmissions
        L               Bound for the maximum time between the
                        decision to transmit a TPDU and the receipt of
                        any response relating to it
        T-WAIT          Maximum time for a reassignment to take place
                        before TC failure is assumed
        I               Inactivity timer - Maximum time allowed to 
                        elapse between receipt of TPDUs before TC 
                        failure is assumed
        W               Window timer - Maximum interval between trans-
                        mission of up to date window information

4.6     Other variables

        n               The number of bits in the sequence number
                        field
        p               The number of bits in the credit field of a 
                        CR, CC or AK TPDU




4.7     Miscellaneous

        TS-user         Transport service user
        TSAP            Transport service access point
        NSAP            Network service access point
        TC              Transport connection
        NC              Network Connection