12.2.3.8   Procedure for transmission of AK TPDUs....... 109
     12.2.3.8.1   Retransmission of AK TPDUs for window
       synchronization
          ................................................... 109
     12.2.3.8.2   Sequence control for transmission  of
       AK TPDUs
          ................................................... 109
     12.2.3.8.3   Retransmission of AK TPDUs after  CDT
       set to zero
          ................................................... 110
     12.2.3.8.4   Retransmission  procedures  following
       reduction of the
          ................................................... 111
     12.2.3.9    Use  of  Flow   Control   Confirmation
       parameter
          ................................................... 112
     12.2.4   Procedures for Release......................... 113
     12.2.4.1   Timers used for Release...................... 113
     12.2.4.2   General Procedures for Release............... 113
     13   STRUCTURE AND ENCODING OF TPDUs.................... 114
     13.1   Validity......................................... 114
     13.2   Structure........................................ 116
     13.2.1   Length indicator field......................... 117
     13.2.2   Fixed part..................................... 117
     13.2.2.1   General...................................... 117
     13.2.2.2   TPDU code.................................... 117
     13.2.3   Variable part.................................. 118
     13.2.3.1   Checksum Parameter (Class 4 only)............ 120
     13.2.4   Data Field..................................... 120
     13.3   Connection Request (CR) TPDU..................... 120
     13.3.1   Structure...................................... 120
     13.3.2   LI............................................. 121
     13.3.3   Fixed Part (Octets 2 to 7)..................... 121
     13.3.4   Variable Part (Octets 8 to p).................. 122
     13.3.5   User Data (Octets p+1 to the end).............. 127
     13.4   Connection Confirm (CC) TPDU..................... 128
     13.4.1   Structure...................................... 128
     13.4.2   LI............................................. 128
     13.4.3   Fixed Part (Octets 2 to 7)..................... 128
     13.4.4   Variable Part (Octet 8 to p)................... 129
     13.4.5   User Data (Octets p+1 to the end).............. 129
     13.5   Disonnect Request (DR) TPDU...................... 129
     13.5.1   Structure...................................... 129

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