tech-invite   World Map
3GPP     Specs     Glossaries     UICC       IETF     RFCs     Groups     SIP     ABNFs       T+       Search     Home

RFC 0905

 
 
 

ISO Transport Protocol specification ISO DP 8073

Part 5 of 5, p. 130 to 164
Prev RFC Part

 


prevText      Top       Page 130 
     13.2.3.1  Checksum Parameter (Class 4 only)

     All TPDU types may contain a 16-bit checksum parameter  in  their
     variable  part.  This parameter shall be present in a CR TPDU and
     shall be present in all other TPDUs except when the  non  use  of
     checksum option is selected.

     Parameter Code:    1100 0011
     Parameter Length:  2
     Parameter Value:   Result of checksum algorithm.  This algorithm
                        is specified in 6.17.




     13.2.4  Data Field

     This field contains transparent user data.  Restrictions  on  its
     size are noted for each TPDU.




     13.3  Connection Request (CR) TPDU

     The length of the CR TPDU shall not exceed 128 octets.




     13.3.1  Structure

     The structure of the CR TPDU shall be as follows:

      1    2        3        4       5   6    7    8    p  p+1...end
     +--+------+---------+---------+---+---+------+-------+---------+
     |LI|CR CDT|     DST - REF     |SRC-REF|CLASS |VARIAB.|USER     |
     |  |1110  |0000 0000|0000 0000|   |   |OPTION|PART   |DATA     |
     +--+------+---------+---------+---+---+------+-------+---------+

Top       Page 131 
     13.3.2  LI

     See 13.2.1




     13.3.3  Fixed Part (Octets 2 to 7)

     The structure of this part shall contain:

        a)  CR       :  Connection Request Code:  1110.  Bits  8-5  of
                        octet 2;

        b)  CDT      :  Initial Credit  Allocation  (set  to  0000  in
                        Classes  0  and  1 when specified as preferred
                        class).  Bits 4-1 of octet 2;

        c)  DST-REF  :  Set to zero;

        d)  SRC-REF  :  Reference selected  by  the  transport  entity
                        initiating   the   CR  TPDU  to  identify  the
                        requested transport connection;

        e)  CLASS and   Bits 8-5 of octet 7 defines the preferred
            OPTION:     transport protocol class to be  operated  over
                        the   requested  transport  connection.   This
                        field shall take one of the following values:

                        0000  Class 0
                        0001  Class 1
                        0010  Class 2
                        0011  Class 3
                        0100  Class 4

     The CR TPDU contains the first choice of class in the fixed part.
     Second  and subsequent choices are listed in the variable part if
     required.

     Bits 4-1 of octet 7 define options to be used  on  the  requested
     transport connection as follows:

Top       Page 132 
     +-----|-----------------------------------------------+
     | BIT |                  OPTION                       |
     |-----|-----------------------------------------------|
     |  4  |  0   always                                   |
     |     |                                               |
     |  3  |  0   always                                   |
     |     |                                               |
     |  2  | =0   use of normal formats in all classes     |
     |     | =1   use of extended formats in Classes 2,3,4 |
     |     |                                               |
     |  1  | =0   use of explicit flow control in Class 2  |
     |     | =1   no use of explicit flow control in       |
     |     |      Class 2                                  |
     +-----------------------------------------------------+


     NOTES

     1.  The connection establishment procedure  (see  6.5)  does  not
         permit  a given CR TPDU to request use of transport expedited
         data transfer service (additional option  parameter)  and  no
         use of explicit flow control in Class 2 (bit 1 = 1).

     2.  Bits 4 to 1 are always zero in Class 0 and have no meaning.




     13.3.4  Variable Part (Octets 8 to p)

     The following parameters are permitted in the variable part:

        a)  Transport Service Access Point Identifier (TSAP-ID)

            Parameter code:    1100 0001 for  the  identifier  of  the
                               Calling TSAP.
                               1100 0010 for  the  identifier  of  the
                               Called TSAP
            Parameter length:  not defined in this standard
            Parameter value:   identifier of  the  calling  or  called
                               TSAP respectively.

Top       Page 133 
            If a TSAP-ID is given in the request it may be returned in
            the confirmation.

        b)  TPDU size

            This parameter defines the proposed maximum TPDU size  (in
            octets including the header) to be used over the requested
            transport connection.  The coding of this parameter is:

            Parameter code:    1100 0000
            Parameter Length:  1 octet

            Parameter value:

            0000 1101  8192 octets (not allowed in Class 0)
            0000 1100  4096 octets (not allowed in Class 0)
            0000 1011  2048 octets
            0000 1010  1024 octets
            0000 1001   512 octets
            0000 1000   256 octets
            0000 0111   128 octets

            Default value is 0000 0111 (128 octets)

        c)  Version Number (not used  if  Class  0  is  the  preferred
            class)

            Parameter code:         1100 0100
            Parameter length:       1 octet
            Parameter value field:  0000 0001

            Default value is 0000 0001 (not used in Class 0)

        d)  Security Parameters (not used if Class 0 is the  preferred
            class)

            This parameter is user defined.
            Parameter code:    1100 0101
            Parameter length:  user defined
            Parameter value:   user defined

        e)  Checksum (used only if class 4  is  the  preferred  class)
            (see 13.2.3.1)

Top       Page 134 
            This parameter shall  always  be  present  in  a  CR  TPDU
            requesting   Class  4,  even  if  the  checksum  selection
            parameter is used  to  request  non-use  of  the  checksum
            facility.

        f)  Additional Option Selection (not used if Class  0  is  the
            preferred class)

            This parameter defines the selection  to  be  made  as  to
            whether or not additional options are to be used.

            Parameter code:    1100 0110
            Parameter length:  1
            Parameter value:


            +------------------------------------------------------+
            |BIT|                   OPTION                         |
            |---|--------------------------------------------------|
            | 4 | 1=  Use of network expedited in Class 1          |
            |   | 0=  Non use of network expedited in Class 1      |
            |   |                                                  |
            | 3 | 1=  Use of receipt confirmation in Class 1       |
            |   | 0=  Use of explicit AK variant in Class 1        |
            |   |                                                  |
            | 2 | 0=  16-bit checksum defined in 6.17 is to be used|
            |   |     in Class 4                                   |
            |   | 1=  16-bit checksum defined in 6.17 is not to be |
            |   |     used on Class 4                              |
            |   |                                                  |
            | 1 | 1=  Use of transport expedited data transfer     |
            |   |     service                                      |
            |   | 0=  No use of transport expedited data transfer  |
            |   |     service                                      |
            +------------------------------------------------------+

            Default value is 000 0001

            Bits related to options particular  to  a  class  are  not
            meaningful  if that class is not proposed and may take any
            value.

Top       Page 135 
        g)  Alternative protocol class(es) (not used if Class 0 is the
            preferred class)

            Parameter code:    1100 0111
            Parameter length:  n

            Parameter value encoded as a sequence  of  single  octets.
            Each octet is encoded as for octet 7 but with bits 4-1 set
            to zero (i.e. no alternative option selections permitted).

        h)  Acknowledge Time (used only if class 4  is  the  preferred
            class)

            This parameter conveys the maximum acknowledge time AL  to
            the  remote  transport  entity.  It is an indication only,
            and is not subject to negotiation (see 12.2.1.1.3)
            Parameter code:    1000 0101
            Parameter length:  2
            Parameter value:   n, a binary number where n is the
                               maximum acknowledge time, expressed
                               in milliseconds.

        j)  Throughput (not used if class 0 is the preferred class)

            Parameter code:    1000 1001
            Parameter length:  12 or 24
            Parameter value:

            1st 12 Octets:     maximum throughput, as follows:

            1st 3 octets:      Target   value,   calling-called   user
                               direction
            2nd 3 octets:      Min.  acceptable,  calling-called  user
                               direction
            3rd 3 octets:      Target   value,   called-calling   user
                               direction
            4th 3 octets:      Min.  acceptable,  called-calling  user
                               direction

            2nd 12 octets (optional):  average throughput, as follows:

            5th 3 octets:      Target   value,   calling-called   user
                               direction

Top       Page 136 
            6th 3 octets:      Min.  acceptable,  calling-called  user
                               direction
            7th 3 octets:      Target   value,   called-calling   user
                               direction
            8th 3 octets:      Min.  acceptable,  called-calling  user
                               direction

            Where the average throughput is omitted, it is  considered
            to have the same value as the maximum throughput.

            Values are expressed in octets per second.

        k)  Residual error rate (not used if class 0 is the  preferred
            class)

            Parameter code:    1000 1001
            Parameter length:  12
            1st 3 octets:      Target   value,   calling-called   user
                               direction
            2nd 3 octets:      Min.  acceptable,  calling-called  user
                               direction
            3rd 3 octets:      Target   value,   called-calling   user
                               direction
            4th 3 octets:      Min.  acceptable,  called-calling  user
                               direction

        l)  Residual error rate (not used if class 0 is the  preferred
            class)

            Parameter code:    1000 0110
            Parameter length:  3
            Parameter value:
            1st octet:         Target value, power of 10
            2nd octet:         Min. acceptable, power of 10
            3rd octet:         TSDU size of interest, expressed  as  a
                               power of 2

        m)  Priority (not used if class 0 is the preferred class)

            Parameter code:    1000 0111
            Parameter length:  2
            Parameter value:   Integer (0 is the highest priority)

Top       Page 137 
        n)  Transit delay (not used if class 0 is the preferred class)

            Parameter code:    1000 1000
            Parameter length:  8
            Parameter value:
            1st 2 octets:      Target   value,   calling-called   user
                               direction
            2nd 2 octets:      Max.  acceptable,  calling-called  user
                               direction
            3rd 2 octets:      Target   value,   called-calling   user
                               direction
            4th 2 octets:      Max.  acceptable,  called-calling  user
                               direction

            Values are expressed in milliseconds, and are based upon a
            TSDU size of 128 octets.

        p)  assignment time (not used if class 0, 2 or class 4 is  the
            preferred class)

            This parameter conveys the Time to Try Reassignment  (TTR)
            which  will  be  used  when  following  the  procedure for
            Reassignment after Failure (see 6.12).
            Parameter code:    1000 1011
            Parameter length:  2
            Parameter value:   n, a binary number where n is  the  TTR
                               value expressed in seconds.




     13.3.5  User Data (Octets p+1 to the end)

     No user data are permitted in Class 0, and are  optional  in  the
     other classes.  Where permitted, it may not exceed 32 octets.

Top       Page 138 
     13.4  Connection Confirm (CC) TPDU

     13.4.1  Structure

     The structure of the CC TPDU shall be as follows:

       1      2     3   4   5   6     7     8     p   p+1 ...end
     +---+----+---+---+---+---+---+-------+--------+-------------+
     |LI | CC  CDT|DST-REF|SRC-REF| CLASS |VARIABLE| USER        |
     |   |1101|   |   |   |   |   | OPTION|  PART  | DATA        |
     +---+----+---+---+---+---+---+-------+--------+-------------+




     13.4.2  LI

     See 13.2.1




     13.4.3  Fixed Part (Octets 2 to 7)

     The fixed part shall contain:

        a)  CC:  Connection Confirm Code:  1101.  Bits 8-5 of octet 2;

        b)  CDT:  Initial Credit Allocation (set to 0000 in Classes  0
            and 1).  Bits 4-1 of octet 2;

        c)  DST-REF:  Reference identifying  the  requested  transport
            connection at the remote transport entity;

        d)  SRC-REF:  Reference identifying  the  requested  transport
            connection at the remote transport entity.

        e)  Class and Option:  Defines the selected transport protocol
            class   and  option  to  be  operated  over  the  accepted
            transport connection according to  the  negotiation  rules
            specified in 6.5;

Top       Page 139 
     13.4.4  Variable Part (Octet 8 to p)

     The parameters are defined in  13.3.4  and  are  subject  to  the
     constraints states in 6.5 (connection establishment).  Parameters
     ruled out by selection of an alternative class and  option  shall
     not be present.




     13.4.5  User Data (Octets p+1 to the end)

     No user data are permitted in class 0, and are  optional  in  the
     other  classes.   Where  permitted,  it may not exceed 32 octets.
     The user data are subject to the constraints of  the  negotiation
     rules (see 6.5).




     13.5  Disonnect Request (DR) TPDU

     13.5.1  Structure

     The structure of the DR TPDU shall be as follows:

       1     2      3     4    5     6     7    8     p   p+1 ...end
     +--+---------+----+-----+----+-----+------+--------+----------+
     |LI|    DR   | DST-REF. | SRC-REF. |REASON|VARIABLE| USER     |
     |  |1000 0001|    |     |    |     |      |  PART  | DATA     |
     +--+---------+----+-----+----+-----+------+--------+----------+




     13.5.2  LI

     See Section 13.2.1

Top       Page 140 
     13.5.3  Fixed Part (Octets 2 to 7

     The fixed part shall contain:

        a)  DR:  Disconnect Request Code:  1000 0000;

        b)  DST-REF:  Reference identifying the  transport  connection
            at the remote transport entity;

        c)  SRC-REF:  Reference identifying the  transport  connection
            at  the  transport entity initiating the TPDU.  Value zero
            when reference is unassigned;

        d)  REASON:   Defines  the  reason   for   disconnecting   the
            transport  connection.   This  field shall take one of the
            following values:

            The following values may be used for Classes 1 to 4:

            1)  128 + 0 - Normal  disconnect  initiated   by   session
                   entity
            2)  128 + 1 - Remote  transport   entity   congestion   at
                   connect request time
            3) *128 + 2 - Connection negotiation failed (i.e. proposed
                   class(es) not supported)
            4)  128 + 3 - Duplicate source reference detected for  the
                   same pair of NSAPS.
            5)  128 + 4 - Mismatched references
            6)  128 + 5 - Protocol error
            7)  128 + 6 - Not used
            8)  128 + 7 - Reference overflow
            9)  128 + 8 - Connection request refused on  this  network
                   connection
            10) 128 + 9 - Not used
            11) 128 + 10- Header or parameter length invalid

Top       Page 141 
        The following values can be used for all classes:

            12)       0 - Reason not specified
            13)       1 - Congestion at TSAP
            14)      *2 - Session entity not attached to TSAP
            15)      *3 - Address unknown

        NOTE - Reasons marked with an asterisk (*) may be reported  to
        the TS-user as persistent, other reasons as transient.




     13.5.4  Variable Part (Octets 8 to p)

     The variable part may contain

        a)  A parameter allowing additional information related to the
            clearing of the connection.

            Parameter code:    1110 0000
            Parameter length:  Any value provided that the  length  of
                               the DR TPDU does not exceed the maximum
                               agreed TPDU size or  128  when  the  DR
                               TPDU  is  used  during  the  connection
                               refusal procedure
            Parameter value:   Additional information.  The content of
                               this field is user defined.

        b)  Checksum (see 13.2.3.1)




     13.5.5  User Data (Octets p+1 to the end)

     This field shall not exceed 64 octets and is used  to  carry  TS-
     user   data.   The  successful  transfer  of  this  data  is  not
     guaranteed by the transport protocol.  When a DR TPDU is used  in
     Class 0 it shall not contain this field.

Top       Page 142 
     13.6  Disconnect Confirm (DC) TPDU

     This TPDU shall not be used in Class 0.




     13.6.1  Structure

     The structure of DC TPDU shall be as follows:

       1       2         3     4     5     6    7        p
     +----+-----------+-----+-----+-----+-----+-------+--------+
     | LI |    DC     |  DST REF  |  SRC REF  | Variable Part  |
     |    | 1100 0000 |     |     |     |     |       |        |
     +----+-----------+-----+-----+-----+-----+-------+--------+




     13.6.2  LI

     See 13.2.1




     13.6.3  Fixed Part (Octets 2 to 6)

     The fixed part shall contain:

        a)  DC:  Disconnect Confirm Code:  1100 0000;

        b)  DST-REF:  See 13.4.3;

        c)  SRC-REF:  See 13.4.3.

Top       Page 143 
     13.6.4  Variable Part

     The variable part shall contain the  checksum  parameter  if  the
     condition in (see 13.2.3.1) applies.




     13.7  Data (DT) TPDU

     13.7.1  Structure

     Depending on the class and the option the DT TPDU shall have  one
     of the following structures.

        a)  Normal format for Classes 0 and 1

       1       2         3          4       5             ... end
     +----+-----------+-----------+------------ - - - - - -------+
     | LI |    DT     |  TPDU-NR  | User Data                    |
     |    | 1111 0000 |  and EOT  |                              |
     +----+-----------+-----------+------------ - - - - - -------+


        b)  Normal format for Classes 2, 3 and 4

       1      2       3   4     5     6       p    p+1       ... end
     +----+---------+---+---+-------+-----+-------+----------- - - -+
     | LI |   DT    |DST-REF|TPDU-NR|Variable Part|User Data        |
     |    |1111 0000|   |   |and EOT|     |       |                 |
     +----+---------+---+---+-------+-----+-------+----------- - - -+

        c)  Extended Format for  use  in  Classes  2,  3  and  4  when
            selected during connection establishment.

       1      2       3   4   5,6 7,8  9     p  p+1      ... end
     +----+---------+---+---+---------+--------+---------- - - -+
     | LI |   DT    |DST-REF| TPDU-NR |Variable|User Data       |
     |    |1111 0000|   |   | and EOT |  Part  |                |
     +----+---------+---+---+---------+--------+---------- - - -+

Top       Page 144 
     13.7.2  LI

     See 13.2.1




     13.7.3  Fixed Part

     The fixed part shall contain:

        a)  DT:       Data Transfer Code:  1111 0000;

        b)  DST-REF:  See 13.4.3;

        c)  EOT:      When set to ONE, indicates that the  current  DT
                      TPDU is the last data unit of a complete DT TPDU
                      sequence (End of TSDU).  EOT is bit 8 of octet 3
                      in  class  0  and 1, bit 8 of octet 5 for normal
                      formats for classes 2, 3 and  4  and  bit  8  of
                      octet 8 for extended formats;

        d)  TPDU-NR:  TPDU send Sequence Number  (zero  in  Class  0).
                      May  take  any value in Class 2 without explicit
                      flow control.  TPDU-NR is bits 7-1  of  octet  3
                      for  classes  0  and  1, bits 7-1 of octet 5 for
                      normal formats in classes 2, 3 and 4, octets  5,
                      6  and  7  together with bits 7-1 of octet 8 for
                      extended formats.

        NOTE - Depending on the class, the fixed part of the  DT  TPDU
        uses the following octets:

             Classes 0 and 1:                Octets 2 to 3;
             Classes 2,3,4 normal format:    Octets 2 to 5;
             Classes 2,3,4 extended format:  Octets 2 to 8.

Top       Page 145 
     13.7.4  Variable Part

     The variable part shall contain the  checksum  parameter  if  the
     condition in see 13.2.3.1 applies.




     13.7.5  User Data Field

     This field contains data of the TSDU being transmitted.

     NOTE - The length of this field is limited to the negotiated TPDU
     size  for  this  transport connection minus 3 octets in Classes 0
     and 1, and minus 5 octets (normal  header  format)  or  8  octets
     (extended  header  format)  in  the  other classes.  The variable
     part, if present, may further reduce the size of  the  user  data
     field.




     13.8  Expedited Data (ED) TPDU

     The ED TPDU shall not be used in Class 0 or in Class 2  when  the
     no explicit flow control option is selected or when the expedited
     data transfer service has not been selected for the connection.




     13.8.1  Structure

     Depending on the format negotiated  at  connection  establishment
     the ED TPDU shall have one of the following structures:

Top       Page 146 
        a)  Normal Format (classes 1, 2, 3, 4)

      1     2       3   4      5     6        p    p+1     ... end
     +--+---------+---+---+---------+-----+-------+---------------+
     |LI|   ED    |DST-REF|EDTPDU-NR|Variable Part|User Data      |
     |  |0001 0000|   |   |and EOT  |     |       |               |
     +--+---------+---+---+---------+-----+-------+---------------+


        b)  Extended Format (for use in classes 2, 3, 4 when  selected
            during connection establishment).


      1     2       3   4   5,6,7,8  9        p    p+1     ... end
     +--+---------+---+---+---------+-----+-------+---------------+
     |LI|   ED    |DST-REF|EDTPDU-NR|Variable Part|User Data      |
     |  |0001 0000|   |   |and EOT  |     |       |               |
     +--+---------+---+---+---------+-----+-------+---------------+




     13.8.2  LI

     See 13.2.1




     13.8.3  Fixed Part

     The fixed part shall contain:

        a)  ED:          Expedited Data code:  0001 0000;

        b)  DST-REF:     see 13.4.3;

        c)  ED-TPDU-NR:  Expedited TPDU  identification  number.   ED-
                         TPDU-NR is used in classes 1, 3 and 4 and may
                         take any value in Class 2.  Bits 7-1 of octet
                         5  for  normal  formats and octets 5, 6 and 7
                         together  with  bits  7-1  of  octet  8   for
                         extended formats;

Top       Page 147 
        d)  EOT:         end of TSDU always set to 1 (bit 8 of octet 5
                         for  normal  formats and bit 8 of octet 8 for
                         extended formats).

        NOTE - Depending on the format the fixed part shall be  either
        octets 2 to 5 or 2 to 8.




     13.8.4  Variable Part

     The variable part shall contain the  checksum  parameter  if  the
     condition defined in 13.2.3.1 applies.




     13.8.5  User Data Field

     This field contains an expedited TSDU (1 to 16 octets).




     13.9  Data Acknowledgement (AK) TPDU

     This TPDU shall not be used for Class 0 and Class 2 when the  "no
     explicit  flow  control" option is selected, and for Class 1 when
     the network receipt confirmation option is selected.




     13.9.1  Structure

     Depending on the class and option agreed the AK TPDU  shall  have
     one of the following structures:

Top       Page 148 
        a)  Normal Format (classes 1, 2, 3, 4)

      1     2      3     4        5        6        p
     +--+--------+----------+------------+---------------+
     |LI| AK CDT | DST-REF  |  YR-TU-NR  | Variable Part |
     |  | 0110   |          |            |               |
     +--+--------+----------+------------+---------------+

        b)  Extended Format (for use in classes 2, 3, 4 when  selected
            during connection establishment).

      1      2      3     4    5,6,7,8   9,10 11    p
     +--+---------+---------+----------+-----+--------+
     |LI|    AK   | DST-REF | YR-TU-NR | CDT |Variable|
     |  |0110 0000|         |          |     |  Part  |
     +--+---------+---------+----------+-----+--------+




     13.9.2  LI

     See 13.2.1




     13.9.3  Fixed Part

     The fixed part shall contain (in octet 2 to 5 when normal  format
     is used, 2 to 10 otherwise) the following parameters:

        a)  AK:        Acknowledgement code:  0110;

        b)  CDT:       Credit Value (set to 1111 in  class  1).   Bits
                       4-1  of octet 2 for normal formats and octets 9
                       and 10 for extended formats;

        c)  DST-REF:   See 13.4.3;

        d)  YR-TU-NR:  Sequence number indicating the next expected DT
                       TPDU  number.   For normal formats, bits 7-1 of
                       octet 5; bit 8 of octet 5  is  not  significant

Top       Page 149 
                       and  shall  take  the  value  0.   For extended
                       formats, octets 5, 6 and 7 together  with  bits
                       7-1  of  octet  8;  bit  8  of  octet  8 is not
                       significant and shall take the value 0.




     13.9.4  Variable Part

     The variable part contains the following parameters:

        a)  Checksum  See  13.2.3.1  if  the  condition  in   13.2.3.1
            applies;

        b)  Subsequence  number  when  optionally   used   under   the
            conditions  defined in class 4.  This parameter is used to
            ensure  that  AK  TPDUs  are  processed  in  the   correct
            sequence.    If  it  is  absent,  this  is  equivalent  to
            transmitting the parameter with a value of zero.
            Parameter code:    1000 1010
            Parameter length:  2
            Parameter value:   16-bit sub-sequence number;

        c)  Flow Control Confirmation Class  4  when  optionally  used
            under  the  conditions defined in class 4.  This parameter
            contains a copy of the information received in an AK TPDU,
            to  allow  the transmitter of the AK TPDU to be certain of
            the  state  of  the  receiving   transport   entity   (see
            12.2.3.10).
            Parameter code:    1000 1011
            Parameter length:  8
            Parameter value:   defined as follows

            1.  Lower Window Edge (32 bits)
                Bit 8 of  octet  4  is  set  to  zero,  the  remainder
                contains  the  YR-TU-NR value of the received AK TPDU.
                When normal format has been selected, only  the  least
                significant  seven  bits  (bits  1 to 7 of octet 1) of
                this field are significant.

            2.  Your Sub-Sequence (16 bits)
                Contains the value of the  sub-sequence  parameter  of

Top       Page 150 
                the  received  AK  TPDU, or zero if this parameter was
                not present.

            3.  Your Credit (16 bits)
                Contains the value of the CDT field of the received AK
                TPDU.   When normal format has been selected, only the
                least significant four bits (bits 1 to 4 of  octet  1)
                of this field are significant.




     13.10  Expedited Data Acknowledgement (EA) TPDU

     This TPDU shall not be used for Class 0 and Class 2 when  the  no
     explicit flow control option is selected.




     13.10.1  Structure

     Depending on the option (normal  or  extended  format)  the  TPDU
     structure shall be:

        a)  Normal Format (classes 1,2,3,4)

             1      2      3     4      5      6        p
            +--+---------+---------+----------+------+------+
            |LI|   EA    | DST-REF | YR-TU-NR |Variable Part|
            |  |0010 0000|         |          |      |      |
            +--+---------+---------+----------+------+------+

        b)  Extended Format (for use in classes 2, 3,  4  if  selected
            during connection establishment)

             1      2      3     4    5,6,7,8  9        p
            +--+---------+---------+----------+------+------+
            |LI|   EA    | DST-REF | YR-TU-NR |Variable Part|
            |  |0010 0000|         |          |      |      |
            +--+---------+---------+----------+------+------+

Top       Page 151 
     13.10.2  LI

     See 13.2.1




     13.10.3  Fixed Part

     The fixed part shall contain (in octets 2 to 5 when normal format
     is used, in octets 2 to 8 otherwise):

        a)  EA:          Expedited Acknowledgement code:  0010 0000;

        b)  DST-REF:     See 13.4.3;

        c)  YR-EDTU-NR:  Identification   of   the   ED   TPDU   being
                         acknowledged.  May take any value in Class 2;

                         For normal formats bits 7-1 of octet 5; bit 8
                         of  octet 5 is not significant and shall take
                         the value 0.  For  extended  formats,  octets
                         5,6  and 7 together with bits 7-1 of octet 8;
                         bit 8 of octet 8 is not significant and shall
                         take the value 0.




     13.10.4  Variable Part

     The  variable  part  may  contain  the  checksum  parameter  (see
     13.2.3.1).




     13.11  Reject (RJ) TPDU

     The RJ TPDU shall not be used in Classes 0, 2 and 4.

Top       Page 152 
     13.11.1  Structure

     The RJ TPDU shall have one of the following formats:

        a)  Normal Format (classes 1 and 3)

              1      2        3     4       5
            +----+----------+----+----+------------+
            | LI |  RJ CDT  | DST-REF |  YR-TU-NR  |
            |    | 0101     |    |    |            |
            +----+----------+----+----+------------+

        b)  Extended Format (for use in classes 3 if  selected  during
            connection establishment).

             1       2       3     4   5,6,7,8   9,10
            +--+-----------+----+----+----------+-----+
            |LI|     RJ    | DST-REF | YR-TU-NR | CDT |
            |  | 0101 0000 |    |    |          |     |
            +--+-----------+----+----+----------+-----+




     13.11.2  LI

     See 13.2.1.




     13.11.3  Fixed Part

     The fixed part shall contain (in octets 2 to 5 when normal format
     is used, in octets 2 to 10 otherwise):

        a)  RJ:        Reject Code:  0101.  Bits 8-5 of octet 2;

        b)  CDT:       Credit Value (set to 1111 in  class  1).   Bits
                       4-1  of octet 2 for normal formats and octets 9
                       and 10 for extended formats;

        c)  DST-REF:   See 13.4.3;

Top       Page 153 
        d)  YR-TU-NR:  Sequence number indicating  the  next  expected
                       TPDU from which retransmission should occur.

                       For normal formats, bits 7-1 of octet 5; bit  8
                       of  octet  5  is not significant and shall take
                       the value 0.  For extended formats, octets  5,6
                       and  7 together with bits 7-1 of octet 8; bit 8
                       of octet 8 is not significant  and  shall  take
                       the value 0.




     13.11.4  Variable Part

     There is no variable part for this TPDU type.




     13.12  TPDU Error (ER) TPDU

     13.12.1  Structure

       1        2       3     4     5         6   P
     +----+-----------+----+----+--------+----------+
     | LI |    ER     | DST-REF | Reject | Variable |
     |    | 0111 0000 |    |    | Cause  |   Part   |
     +----+-----------+----+----+--------+----------+




     13.12.2  LI

     See 13.2.1

Top       Page 154 
     13.12.3  Fixed Part

     The fixed part shall contain:

        a)  ER:            TPDU Error Code:  0111 0000;

        b)  DST-REF:       See 13.4.3;

        c)  REJECT CAUSE:  0000 0000  Reason not specified
                           0000 0001  Invalid parameter code
                           0000 0010  Invalid TPDU type
                           0000 0011  Invalid parameter value.




     13.12.4  Variable Part

     The variable part may contain the following parameters:

        a)  Invalid TPDU

            Parameter code:    1100 0001

            Parameter length:  number of octets of the value field

            Parameter Value:  Contains the bit pattern of the rejected
                               TPDU  up  to  and  including  the octet
                               which  caused  the   rejection.    This
                               parameter is mandatory in Class 0.

        b)  Checksum

            This parameter  shall  be  present  if  the  condition  in
            13.2.3.1 applies.

Top       Page 155 
     SECTION THREE.  CONFORMANCE




     14  CONFORMANCE

     14.1

     A system claiming to implement the procedures specified  in  this
     standard shall comply with the requirements in 14.2 - 14.5.




     14.2

     The system shall implement Class 0 or Class 2 or both.




     14.3

     If the system implements Class  3  or  Class  4,  it  shall  also
     implement Class 2.




     14.4

     If the system implements Class 1, it shall also  implement  Class
     0.

Top       Page 156 
     14.5

     For each class which the system claims to implement,  the  system
     shall be capable of:

        a)  initiating CR TPDUs or responding  to  CR  TPDUs  with  CC
            TPDUs or both;

        b)  responding to any other TPDU and operating network service
            in accordance with the procedures for the class;

        c)  operating all the  procedures  for  the  class  listed  as
            mandatory in table 9;

        d)  operating  those  procedures  for  the  class  listed   as
            optional in table 9 for which conformance is claimed;

        e)  handling all TPDUs of lengths up to the lesser value of:

            1)  the maximum length for the class;

            2)  the maximum for which conformance is claimed.

            NOTE - This requirement indicates that TPDU sizes  of  128
            octets are always implemented.




     14.6  Claims of Conformance Shall State

        a)  which class or classes of protocol are implemented;

        b)  whether the system is capable of initiating or  responding
            to CR TPDUs or both;

        c)  which of the procedures listed as optional in table 9  are
            implemented;

Top       Page 157 
        d)  the maximum size of TPDU implemented; the value  shall  be
            chosen  from the following list and all values in the list
            which are less than this maximum shall be implemented:

            128, 256, 512, 1024, 2048, 4096 or 8192 octets.

Top       Page 158 
     +------------------------------------------------------------+
     |       PROCEDURE          |    CLASS 0     |    CLASS 1     |
     |--------------------------|----------------|----------------|
     |                          |                |                |
     |TPDU with checksum        | NA             | NA             |
     |TPDU wihout checksum      | mandatory      | mandatory      |
     |                          |                |                |
     |--------------------------|----------------|----------------|
     |Expedited data transfer   | NA             | mandatory      |
     |No expedited data transfer| mandatory      | mandatory      |
     |                          |                |                |
     |--------------------------|----------------|----------------|
     |Flow control in Class 2   | NA             | NA             |
     |No flow control in Class 2| NA             | NA             |
     |                          |                |                |
     |--------------------------|----------------|----------------|
     |Normal formats            | mandatory      | mandatory      |
     |Extended formats          | NA             | NA             |
     |                          |                |                |
     |--------------------------|----------------|----------------|
     |Use of receipt confirma-  |                |                |
     |tion in Class 1           | NA             | optional       |
     |No use of receipt con-    |                |                |
     |firmation in Class 1      | NA             | mandatory      |
     |                          |                |                |
     |--------------------------|----------------|----------------|
     |Use of network expedited  |                |                |
     |in Class 1                | NA             | optional       |
     |No use of network expedi- |                |                |
     |ted in Class 1            | NA             | mandatory      |
     |                          |                |                |
     +------------------------------------------------------------+

     NA indicates the procedure is not applicable.
             Table 9. (First of 2 pages) Provision of options

Top       Page 159 
     +------------------------------------------------------------+
     |       PROCEDURE          | CLASS 2  | CLASS 3  |  CLASS 4  |
     |--------------------------|----------|----------|-----------|
     |                          |          |          |           |
     |TPDU with checksum        |NA        |NA        |mandatory  |
     |TPDU wihout checksum      |mandatory |mandatory |optional   |
     |                          |          |          |           |
     |--------------------------|----------|----------|-----------|
     |Expedited data transfer   |mandatory |mandatory |mandatory  |
     |No expedited data transfer|mandatory |mandatory |mandatory  |
     |                          |          |          |           |
     |--------------------------|----------|----------|-----------|
     |Flow control in Class 2   |mandatory |NA        |NA         |
     |No flow control in Class 2|optional  |NA        |NA         |
     |                          |          |          |           |
     |--------------------------|----------|----------|-----------|
     |Normal formats            |mandatory |mandatory |mandatory  |
     |Extended formats          |optional  |optional  |optional   |
     |                          |          |          |           |
     |--------------------------|----------|----------|-----------|
     |Use of receipt confirma-  |          |          |           |
     |tion in Class 1           |NA        |NA        |NA         |
     |No use of receipt con-    |          |          |           |
     |firmation in Class 1      |NA        |NA        |NA         |
     |                          |          |          |           |
     |--------------------------|----------|----------|-----------|
     |Use of network expedited  |          |          |           |
     |in Class 1                |NA        |NA        |NA         |
     |No use of network expedi- |          |          |           |
     |ted in Class 1            |NA        |NA        |NA         |
     |                          |          |          |           |
     +------------------------------------------------------------+

     NA indicates the procedure is not applicable
            Table 9. (Second of 2 pages) Provision of options

Top       Page 160 
     ANNEX A - STATE TABLES


     This annex is an integral part of the body of this  International
     Standard.

     This Annex provides a more precise description of  the  protocol.
     In  the  event  of a discrepancy between the description in these
     tables and that contained in the text, the text takes precedence.

     The state table also  define  the  mapping  between  service  and
     protocol events that TS-users can expect.

     This annex describes the transport protocol  in  terms  of  state
     tables.    The  state  tables  show  the  state  of  a  transport
     connection, the events that occur in the  protocol,  the  actions
     taken and the resultant state.

     [The state tables have been omitted from this copy.]

Top       Page 161 
     ANNEX B - CHECKSUM ALGORITHMS

     (This annex is provided for information for implementors  and  is
     not an integral part of the body of the standard.)



     B.1  SYMBOLS

     The following symbols are used:

        C0  variables used in the algorithms
        C1

        i   number (i.e. position) of an octet within  the  TPDU  (see
            12.1)

        n   number (i.e. position) of the first octet of the  checksum
            parameter

        L   length of the complete TPDU

        X   value of the first octet of the checksum parameter

        Y   value of the second octet of the checksum parameter.



     B.2  ARITHMETIC CONVENTIONS

     Addition is performed in one of the two following modes:

        a)  modulo 255 arithmetic;

        b)  one's  complement  arithmetic  in  which  if  any  of  the
            variables  has the value minus zero (i.e. 255) it shall be
            regarded as though it was plus zero (i.e. 0).



     B.3  ALGORITHM FOR GENERATING CHECKSUM PARAMETERS

Top       Page 162 
     B.3.1  Set up the complete TPDU with the value  of  the  checksum
     parameter field set to zero.


     B.3.2  Initialize C0 and C1 to zero.



     B.3.3  Process each octet sequentially from i = 1 to L by:

        a)  adding the value of the octet to C0; then

        b)  adding the value of C0 to C1.



     B.3.4  Calculate X and Y such that

        X = -C1 + (L-n).CO
        Y =  C1 - (L-n+1).C0



     B.3.5  Place the values  X  and  Y  in  octets  n  and  (n  +  1)
     respectively.

     [A Note describing the above algorithm in  mathematical  notation
     has been omitted from this copy.]



     B.4  ALGORITHM FOR CHECKING CHECKSUM PARAMETERS


     B.4.1  Initialize C0 and C1 to zero.


     B.4.2  Process each octet of the TPDU sequentially from i = 1  to
     L by:

        a)  adding the value of the octet to C0; then

        b)  adding the value of C0 to C1.

Top       Page 163 
     B.4.3  If, when all the octets have  been  processed,  either  or
     both  of  C0  and  C1  does not have the value zero, the checksum
     formulas in 6.17 have not been satisfied.

     NOTE - The nature of  the  algorithm  is  such  that  it  is  not
     necessary to compare explicitly the stored checksum bytes.

Top       Page 164 
     Explanatory Report

     The Transport Layer Services and Protocols have been under  study
     within  TC97/SC16  since  1979.   It  was  agreed  by SC16 at its
     meeting in Berlin, November 1980, that the Service  and  Protocol
     documents would be progressed concurrently.

     At the SC16 meeting in Tokyo, June 1982, authorization was  given
     (Resolutions  10  and  11,  SC16  N  1233)  to  register both the
     Transport  Service  Definition   and   the   Transport   Protocol
     Specification  as Draft Proposals and to circulate them for a 90-
     day ballot.

     Following the close of the letter ballot  an  Editing  Group  was
     convened to integrate editorial comments and make recommendations
     regarding proposed technical  changes.   The  revised  texts  and
     proposed recommendations were reviewed by SC16/WG6 at its meeting
     in Vienna, March 1983.  The revised text of the Transport Service
     Definition  (SC16  N  1435) was accepted as presented whereas the
     revised  text  of  the  Transport  Protocol  (SC16  N  1433)  was
     subjected  to  an  additional 60-day ballot.  Consistent with the
     SC16 decision regarding the parallel progression of both DPs, the
     Transport   Service  Definition  was  held  in  abeyance  pending
     acceptance by SC16 of the revised Transport Protocol  (Second  DP
     8073).

     A second Editing Group was  convened  in  Paris,  July  1983,  to
     review  comments  submitted  on  Second DP 8073.  The Minutes and
     Report of this meeting are documented in SC16 N1575  and  N  1574
     respectively.   The  two  negative votes (DIN and NNI) were given
     full consideration.  The NNI concerns have been fully covered  in
     the revised text prepared by the Editing Group.  The DIN concerns
     have been taken into account  and  incorporated  in  their  large
     majority.

     Upon the recommendation of the Editing Group, DP 8072 and DP 8073
     are  forwarded  for registration as Draft International Standards
     and letter ballot of ISO Member Bodies.