RFC 0905
ISO Transport Protocol specification ISO DP 8073
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 | +--+------+---------+---------+---+---+------+-------+---------+
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:
+-----|-----------------------------------------------+
| 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.
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)
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.
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
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)
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.
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;
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
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
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.
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.
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 | | +----+---------+---+---+---------+--------+---------- - - -+
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.
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:
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;
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:
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
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
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| | | | |
+--+---------+---------+----------+------+------+
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.
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;
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
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.
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.
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;
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.
+------------------------------------------------------------+
| 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
+------------------------------------------------------------+
| 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
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.]
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
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.
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.
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.