As per Relevance of the word following, we have this rfc below:
Network Working Group
Request for Comments: 905 April 1984
ISO Transport Protocol
ISO DP 8073
Status of this Memo:
This document is distributed as an RFC for information only.
does not specify a standard for the ARPA-Internet
Notes
1) RFC 892 is an older version of the ISO Transport
Specification. Therefore this RFC should be assumed
supercede RFC 892.
2) This document has been prepared by retyping the text
ISO/TC97/SC16/N1576 and then applying proposed
corrections contained in ISO/TC97/SC16/N1695. These
documents, taken together, are undergoing voting within
as a Draft International Standard (DIS).
3) Although this RFC has been reviewed after typing, and
believed to be substantially correct, it is possible
typographic errors not present in the ISO documents have
overlooked
Alex
Table of
1 SCOPE AND FIELD OF APPLICATION........................ 3
1.1 This International Standard specifies:.............. 3
1.2 The procedures are defined in terms of:............. 4
1.3 .................................................... 4
1.4 .................................................... 5
2 REFERENCES............................................ 5
3 DEFINITIONS........................................... 6
3.1 .................................................... 6
3.2 .................................................... 6
3.2.1 equipment:........................................ 7
3.2.2 transport service user:........................... 7
3.2.3 network service provider:......................... 7
3.2.4 local matter:..................................... 7
3.2.5 initiator:........................................ 7
3.2.6 responder:........................................ 8
3.2.7 sending transport entity:......................... 8
3.2.8 receiving transport entity:....................... 8
3.2.9 preferred class:.................................. 8
3.2.10 alternative class:............................... 8
3.2.11 proposed class:.................................. 9
3.2.12 selected class:.................................. 9
3.2.13 proposed parameter:.............................. 9
3.2.14 selected parameter:.............................. 9
3.2.15 error indication:................................ 9
3.2.16 invalid TPDU:................................... 10
3.2.17 protocol error:................................. 10
3.2.18 sequence number:................................ 10
3.2.19 transmit window:................................ 10
3.2.20 lower window edge:.............................. 11
3.2.21 upper window edge:.............................. 11
3.2.22 upper window edge allocated to the
entity
.................................................... 11
3.2.23 closed window:.................................. 11
3.2.24 window information:............................. 11
3.2.25 frozen reference:............................... 12
3.2.26 unassigned reference:........................... 12
3.2.27 transparent (data):............................. 12
3.2.28 owner (of a network connection):................ 12
3.2.29 retained TPDU:.................................. 12
4 SYMBOLS AND ABBREVIATIONS............................ 13
4.1 Data units......................................... 13
4.2 Types of transport protocol data units............. 13
4.3 TPDU fields........................................ 13
4.4 Times and associated variables..................... 14
4.5 Miscellaneous...................................... 14
5 OVERVIEW OF THE TRANSPORT PROTOCOL................... 15
5.1 Service provided by the transport layer............ 15
5.2 Service assumed from the network layer............. 16
5.3 Functions of the Transport Layer................... 18
5.3.1 Overview of functions............................ 18
5.3.1.1 Functions used at all times.................... 19
5.3.1.2 Connection Establishment....................... 19
5.3.1.3 Data Transfer.................................. 20
5.3.1.4 Release........................................ 21
5.4 Classes and options................................ 21
5.4.1 General.......................................... 21
5.4.2 Negotiation...................................... 22
5.4.3 Choice of network connection..................... 22
5.4.4 Characteristics of Class 0....................... 23
5.4.5 Characteristics of Class 1....................... 23
5.4.6 Characteristics of Class 2....................... 24
5.4.6.1 General........................................ 24
5.4.6.2 Use of explicit flow control................... 24
5.4.6.3 Non-use of explicit flow control............... 24
5.4.7 Characteristics of Class 3....................... 24
5.4.8 Characteristics of Class 4....................... 25
5.5 Model of the transport layer....................... 25
6 ELEMENTS OF PROCEDURE................................ 27
6.1 Assignment to network connection................... 27
6.1.1 Purpose.......................................... 27
6.1.2 Network service primitives....................... 27
6.1.3 Procedure........................................ 28
6.2 Transport protocol data unit (TPDU) transfer....... 29
6.2.1 Purpose.......................................... 29
6.2.2 Network Service Primitives....................... 30
6.2.3 Procedure........................................ 30
6.3 Segmenting and reassembling........................ 30
6.3.1 Purpose.......................................... 30
6.3.2 TPDUs and parameter used......................... 31
6.3.3 Procedure........................................ 31
6.4 Concatenation and separation....................... 31
6.4.1 Purpose.......................................... 31
6.4.2 Procedure........................................ 32
6.5 Connection establishment........................... 32
6.5.1 Purpose.......................................... 32
6.5.2 Network service primitives....................... 33
6.5.3 TPDUs and parameters used........................ 33
6.5.4 Procedure........................................ 34
6.6 Connection refusal................................. 40
6.6.1 Purpose.......................................... 40
6.6.2 TPDUs and parameters used........................ 40
6.6.3 Procedure........................................ 41
6.7 Normal release..................................... 41
6.7.1 Purpose.......................................... 41
6.7.2 Network service primitives....................... 42
6.7.3 TPDUs and parameters used........................ 42
6.7.4 Procedure for implicit variant................... 43
6.7.5 Procedure for explicit variant................... 43
6.8 Error Release...................................... 44
6.8.1 Purpose.......................................... 45
6.8.2 Network service primitives....................... 45
6.8.3 Procedure........................................ 45
6.9 Association of TPDUs with
.................................................... 45
6.9.1 Purpose.......................................... 45
6.9.2 Network service primitives....................... 46
6.9.3 TPDUs and parameters uses........................ 46
6.9.4 Procedures....................................... 46
6.9.4.1 Identification of TPDUs........................ 46
6.9.4.2 Association of individual TPDUs................ 47
6.10 Data TPDU numbering............................... 49
6.10.1 Purpose......................................... 49
6.10.2 TPDUs and parameters used....................... 49
6.10.3 Procedure....................................... 50
6.11 Expedited data transfer........................... 50
6.11.1 Purpose......................................... 50
6.11.2 Network service primitives...................... 50
6.11.3 TPDUs and parameter used........................ 51
6.11.4 Procedures...................................... 51
6.12 Reassignment after failure........................ 52
6.12.1 Purpose......................................... 52
6.12.2 Network service primitives...................... 52
6.12.3 Procedure....................................... 52
6.12.4 Timers.......................................... 54
6.13 Retention until acknowledgement of TPDUs.......... 56
6.13.1 Purpose......................................... 56
6.13.2 Network service primitives...................... 56
6.13.3 TPDUs and parameters used....................... 56
6.13.4 Procedures...................................... 57
6.14 Resynchronization................................. 60
6.14.1 Purpose......................................... 60
6.14.2 Network service primitives...................... 60
6.14.3 TPDUs and parameters used....................... 60
6.14.4 Procedure....................................... 61
6.14.4.1 Active resynchronization procedures........... 61
6.14.4.2 Passive resynchronization procedures.......... 62
6.14.4.3 Data Resynchronization Procedures............. 63
6.15 Multiplexing and demultiplexing................... 64
6.15.1 Purpose......................................... 64
6.15.2 TPDUs and parameters used....................... 64
6.15.3 Procedure....................................... 65
6.16 Explicit Flow Control............................. 65
6.16.1 Purpose......................................... 65
6.16.2 TPDUs and parameters used....................... 65
6.16.3 Procedure....................................... 66
6.17 Checksum.......................................... 66
6.17.1 Purpose......................................... 66
6.17.2 TPDUs and parameters used....................... 66
6.17.3 Procedure....................................... 67
6.18 Frozen references................................. 68
6.18.1 Purpose......................................... 68
6.18.2 Procedure....................................... 68
6.18.2.1 Procedure for classes 0 and 2................. 68
6.18.2.2 Procedure for classes 1 and 3................. 69
6.18.2.3 Procedure for classes 4....................... 70
6.19 Retransmission on time-out........................ 70
6.19.1 Purpose......................................... 70
6.19.2 TPDUs used...................................... 70
6.19.3 Procedure....................................... 70
6.20 Resequencing...................................... 70
6.20.1 Purpose......................................... 71
6.20.2 TPDUs and parameters used....................... 71
6.20.3 Procedure....................................... 71
6.21 Inactivity control................................ 71
6.21.1 Purpose......................................... 71
6.21.2 Procedure....................................... 72
6.22 Treatment of protocol errors...................... 72
6.22.1 Purpose......................................... 72
6.22.2 TPDUs and parameters used....................... 72
6.22.3 Procedure....................................... 72
6.23 Splitting and recombining......................... 74
6.23.1 Purpose......................................... 74
6.23.2 Procedure....................................... 74
7 Protocol Classes..................................... 76
8 SPECIFICATION FOR CLASS 0. SIMPLE CLASS.............. 79
8.1 Functions of class 0............................... 79
8.2 Procedures for class 0............................. 79
8.2.1 Procedures applicable at all times............... 79
8.2.2 Connection establishment......................... 79
8.2.3 Data transfer.................................... 80
8.2.4 Release.......................................... 80
9 SPECIFICATION FOR CLASS 1: BASIC
RECOVERY
.................................................... 81
9.1 Functions of Class 1............................... 81
9.2 Procedures for Class 1............................. 81
9.2.1 Procedures applicable at all times............... 81
9.2.2 Connection establishment......................... 82
9.2.3 Data Transfer.................................... 82
9.2.3.1 General........................................ 82
9.2.3.2 Expedited Data................................. 83
9.2.4 Release.......................................... 84
10 SPECIFICATION FOR CLASS 2 -
.................................................... 85
10.1 Functions of class 2.............................. 85
10.2 Procedures for class 2............................ 85
10.2.1 Procedures applicable at all times.............. 85
10.2.2 Connection establishment........................ 86
10.2.3 Data transfer when non use of
flow
.................................................... 86
10.2.4 Data transfer when use of explicit
.................................................... 86
10.2.4.1 General....................................... 86
10.2.4.2 Flow control.................................. 87
10.2.4.3 Expedited data................................ 88
10.2.5 Release......................................... 89
11 SPECIFICATION FOR CLASS 3: ERROR RECOVERY
MULTIPLEXING
.................................................... 90
11.1 Functions of Class 3.............................. 90
11.2 Procedures for Class 3............................ 90
11.2.1 Procedures applicable at all times.............. 90
11.2.2 Connection Establishment........................ 91
11.2.3 Data Transfer................................... 91
11.2.3.1 General....................................... 91
11.2.3.2 Use of RJ TPDU................................ 92
11.2.3.3 Flow Control.................................. 93
11.2.3.4 Expedited data................................ 93
11.2.4 Release......................................... 94
12 SPECIFICATION FOR CLASS 4: ERROR
AND RECOVERY
.................................................... 95
12.1 Functions of Class 4.............................. 95
12.2 Procedures for Class 4............................ 95
12.2.1 Procedures available at all times............... 95
12.2.1.1 Timers used at all times...................... 95
12.2.1.1.1 NSDU lifetime (MLR, MRL).................... 98
12.2.1.1.2 Expected maximum transit delay (ELR
ERL
.................................................... 98
12.2.1.1.3 Acknowledge Time (AR, AL)................... 99
12.2.1.1.4 Local retransmission time (T1).............. 99
12.2.1.1.5 Persistence Time (R)........................ 99
12.2.1.1.6 Bound on References and
Numbers (L
................................................... 100
12.2.1.2 General Procedures........................... 100
12.2.2 Procedures for Connection Establishment........ 102
12.2.2.1 Timers used in Connection Establishment...... 102
12.2.2.2 General Procedures........................... 103
12.2.3 Procedures for Data Transfer................... 104
12.2.3.1 Timers used in Data Transfer................. 104
12.2.3.2 General Procedures for data transfer......... 104
12.2.3.3 Inactivity Control........................... 105
12.2.3.4 Expedited Data............................... 105
12.2.3.5 Resequencing................................. 106
12.2.3.6 Explicit Flow Control........................ 107
12.2.3.7 Sequencing of received AK TPDUs.............. 108
12.2.3.8 Procedure for transmission of AK TPDUs....... 109
12.2.3.8.1 Retransmission of AK TPDUs for
................................................... 109
12.2.3.8.2 Sequence control for transmission
AK
................................................... 109
12.2.3.8.3 Retransmission of AK TPDUs after
set to
................................................... 110
12.2.3.8.4 Retransmission procedures
reduction of
................................................... 111
12.2.3.9 Use of Flow Control
................................................... 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
13.5.2 LI............................................. 129
13.5.3 Fixed Part (Octets 2 to 7...................... 130
13.5.4 Variable Part (Octets 8 to p).................. 131
13.5.5 User Data (Octets p+1 to the end).............. 131
13.6 Disconnect Confirm (DC) TPDU..................... 132
13.6.1 Structure...................................... 132
13.6.2 LI............................................. 132
13.6.3 Fixed Part (Octets 2 to 6)..................... 132
13.6.4 Variable Part.................................. 133
13.7 Data (DT) TPDU................................... 133
13.7.1 Structure...................................... 133
13.7.2 LI............................................. 134
13.7.3 Fixed Part..................................... 134
13.7.4 Variable Part.................................. 135
13.7.5 User Data Field................................ 135
13.8 Expedited Data (ED) TPDU......................... 135
13.8.1 Structure...................................... 135
13.8.2 LI............................................. 136
13.8.3 Fixed Part..................................... 136
13.8.4 Variable Part.................................. 137
13.8.5 User Data Field................................ 137
13.9 Data Acknowledgement (AK) TPDU................... 137
13.9.1 Structure...................................... 137
13.9.2 LI............................................. 138
13.9.3 Fixed Part..................................... 138
13.9.4 Variable Part.................................. 139
13.10 Expedited Data Acknowledgement (EA) TPDU........ 140
13.10.1 Structure..................................... 140
13.10.2 LI............................................ 141
13.10.3 Fixed Part.................................... 141
13.10.4 Variable Part................................. 141
13.11 Reject (RJ) TPDU................................ 141
13.11.1 Structure..................................... 142
13.11.2 LI............................................ 142
13.11.3 Fixed Part.................................... 142
13.11.4 Variable Part................................. 143
13.12 TPDU Error (ER) TPDU............................ 143
13.12.1 Structure..................................... 143
13.12.2 LI............................................ 143
13.12.3 Fixed Part.................................... 144
13.12.4 Variable Part................................. 144
14 CONFORMANCE........................................ 145
14.1 ................................................. 145
14.2 ................................................. 145
14.3 ................................................. 145
14.4 ................................................. 145
14.5 ................................................. 146
14.6 Claims of Conformance Shall State................ 146
The Transport Protocol Standard is one of a set of
Standards produced to facilitate the interconnection of
systems. The set of standards covers the services and
required to achieve such interconnection
The Transport Protocol Standard is positioned with respect
other related standards by the layers defined in the
Model for Open Systems Interconnection (ISO 7498). It is
closely related to, and lies within the field of application
the Transport Service Standard (DP 8072). It also uses and
reference to the Network Service Standard (DP 8348),
provisions it assumes in order to accomplish the
protocol's aims. The interelationship of these standards
depicted in figure 1.
-------------------------TRANSPORT SERVICE DEFINITION------------
Transport | --- Reference to aims --------------
Protocol |
Specification | --- Reference to assumptions -------
-------------------------NETWORK SERVICE DEFINITION--------------
Relationaship between Transport Protocol and adjacent
Figure 1 .
The International Standard specifies a common encoding and
number of classes of transport protocol procedures to be
with different network qualities of service
It is intended that the Transport Protocol should be simple
general enough to cater for the total range of Network
qualities possible, without restricting future extensions
The protocol is structured to give rise to classes of
which are designed to minimize possible incompatibilities
implementation costs
1
The classes are selectable with respect to the Transport
Network Services in providing the required quality of service
the interconnection of two session entities (note that each
provides a different set of functions for enhancement of
qualities).
This protocol standard defines mechanisms that can be used
optimize network tariffs and enhance the following qualities
service
a) different throughput rates
b) different error rates
c) integrity of data requirements
d) reliability requirements
It does not require an implementation to use all of
mechanisms, nor does it define methods for measuring
quality of service or criteria for deciding when to
transport connections following quality of service degradation
The primary aim of this International Standard is to provide
set of rules for communication expressed in terms of
procedures to be carried out by peer entities at the time
communication. These rules for communication are intended
provide a sound basis for development in order to serve a
of purposes
a) as a guide for implementors and designers
b) for use in the testing and procurement of equipment
c) as part of an agreement for the admittance of systems
the open systems environment
d) as a refinement of the understanding of OSI
It is expected that the initial users of the
Standard will be designers and implementors of equipment and
International Standard contains, in notes or in annexes,
on the implementation of the procedures defined in the standard
2
It should be noted that, as the number of valid
sequences is very large, it is not possible with
technology to verify that an implementation will operate
protocol defined in this International Standard correctly
all circumstances. It is possible by means of testing
establish confidence that an implementation correctly
the protocol in a representative sample of circumstances. It is
however, intended that this International Standard can be used
circumstances where two implementations fail to communicate
order to determine whether one or both have failed to operate
protocol correctly
This International Standard contains a section on conformance
equipment claiming to implement the procedures in
International Standard. Attention is drawn to the fact that
standard does not contain any tests to demonstrate
conformance
The variations and options available within this
Standard are essential to enable a Transport Service to
provided for a wide variety of applications over a variety
network qualities. Thus, a minimally conforming
will not be suitable for use in all possible circumstances.
is important, therefore, to qualify all references to
International Standard with statements of the options provided
required or with statements of the intended purpose of
or use
1 SCOPE AND FIELD OF
1.1 This International Standard specifies
a) five classes of procedures
1) Class 0. Simple class
2) Class 1. Basic error recovery class
3) Class 2. Multiplexing class
4) Class 3. Error recovery and multiplexing class
5) Class 4. Error detection and recovery class
3
for the connection oriented transfer of data and
information from one transport entity to a peer
entity
b) the means of negotiating the class of procedures to
used by the transport entities
c) the structure and encoding of the transport protocol
units used for the transfer of data and
information
1.2 The procedures are defined in terms of
a) the interactions between peer transport entities
the exchange of transport protocol data units
b) the interactions between a transport entity and
transport service user in the same system through
exchange of transport service primitives
c) the interactions between a transport entity and
network service provider through the exchange of
service primitives
These procedures are defined in the main text of the
supplemented by state tables in annex A
1.3
These procedures are applicable to instances of
between systems which support the Transport Layer of the
Reference Model and which wish to interconnect in an open
environment
4
1.4
This International Standard also specifies
requirements for systems implementing these procedures. It
not contain tests which can be used to demonstrate
conformance
2
ISO 7498 Information processing systems - Open
interconnection - Basic Reference
DP 8072 Information processing systems - Open
interconnection - Transport service
DP 8348 Information processing systems - Open
interconnection - Connection-oriented network
definition
5
SECTION ONE.
3
NOTE - The definitions contained in this clause make use
abbreviations defined in clause 4.
3.1
This International Standard is based on the concepts developed
the Reference Model for Open Systems Interconnection (DIS 7498)
and makes use of the following terms defined in that standard
a) concatenation and separation
b) segmenting and reassembling
c) multiplexing and demultiplexing
d) splitting and recombining
e) flow control
3.2
For the purpose of this International Standard, the
definitions apply
6
3.2.1 equipment
Hardware or software or a combination of both; it need not
physically distinct within a computer system
3.2.2 transport service user
An abstract representation of the totality of those
within a single system that make use of the transport service
3.2.3 network service provider
An abstract machine that models the totality of the
providing the network service, as viewed by a transport entity
3.2.4 local matter
A decision made by a system concerning its behavior in
Transport Layer that is not subject to the requirements of
protocol
3.2.5 initiator
A transport entity that initiates a CR TPDU
7
3.2.6 responder
A transport entity with whom an initiator wishes to establish
transport connection
NOTE - Initiator and responder are defined with respect to
single transport connection. A transport entity can be both
initiator and responder simultaneously
3.2.7 sending transport entity
A transport entity that sends a given TPDU
3.2.8 receiving transport entity
A transport entity that receives a given TPDU
3.2.9 preferred class
The protocol class that the initiator indicates in a CR TPDU
its first choice for use over the transport connection
3.2.10 alternative class
A protocol class that the initiator indicates in a CR TPDU as
alternative choice for use over the transport connection
8
3.2.11 proposed class
A preferred class or an alternative class
3.2.12 selected class
The protocol class that the responder indicates in a CC TPDU
it has chosen for use over the transport connection
3.2.13 proposed parameter
The value for a parameter that the initiator indicates in a
TPDU that it wishes to use over the transport connection
3.2.14 selected parameter
The value for a parameter that the responder indicates in a
TPDU that it has chosen for use over the transport connection
3.2.15 error indication
An N-RESET indication, or an N-DISCONNECT indication with
reason code indicating an error, that a transport entity
from the NS-provider
9
3.2.16 invalid TPDU
A TPDU that does not comply with the requirements of
International Standard for structure and encoding
3.2.17 protocol error
A TPDU whose use does not comply with the procedures for
class
3.2.18 sequence number
a) The number in the TPDU-NR field of a DT TPDU
indicates the order in which the DT TPDU was
by a transport entity
b) The number in the YR-TU-NR field of an AK or RJ TPDU
indicates the sequence number of the next DT TPDU
to be received by a transport entity
3.2.19 transmit window
The set of consecutive sequence numbers which a transport
has been authorized by its peer entity to send at a given time
a given transport connection
10
3.2.20 lower window edge
The lowest sequence number in a transmit window
3.2.21 upper window edge
The sequence number which is one greater than the
sequence number in the transmit window
3.2.22 upper window edge allocated to the peer entity
The value that a transport entity communicates to its peer
to be interpreted as its new upper window edge
3.2.23 closed window
A transmit window that contains no sequence number
3.2.24 window information
Information contained in a TPDU relating to the upper and
lower window edges
11
3.2.25 frozen reference
A reference that is not available for assignment to a
because of the requirements of 6.18.
3.2.26 unassigned reference
A reference that is neither currently in use for identifying
transport connection or which is in a frozen state
3.2.27 transparent (data):
TS-user data that is transferred intact between
entities and which is unavailable for use by the
entities
3.2.28 owner (of a network connection):
The transport entity that issued the N-CONNECT request leading
the creation of that network connection
3.2.29 retained TPDU
A TPDU that is subject to the retransmission procedure
retention until acknowledgement procedure and is available
possible retransmission
12
4 SYMBOLS AND
4.1 Data
TPDU Transport protocol data
TSDU Transport service data
NSDU Network service data
4.2 Types of transport protocol data
CR TPDU Connection request
CC TPDU Connection confirm
DR TPDU Disconnect request
DC TPDU Disconnect confirm
DT TPDU Data
ED TPDU Expedited data
AK TPDU Data acknowledge
EA TPDU Expedited acknowledge
RJ TPDU Reject
ER TPDU Error
4.3 TPDU
LI Length indicator (field
CDT Credit (field
TSAP-ID Transport service access
identifier (field
DST-REF Destination reference (field
SRC-REF Source reference (field
EOT End of TSDU
TPDU-NR DT TPDU number (field
ED-TPDU-NR ED TPDU number (field
YR-TU-NR Sequence number response (field
YR-EDTU-NR ED TPDU number response (field
13
4.4 Times and associated
T1 Elapsed time between
N The maximum number of
L Bound on
I Inactivity
W Window
TTR Time to try reassignment/
TWR Time to wait
reassignment/
TS1 Supervisory timer 1
TS2 Supervisory time 2
MLR NSDU lifetime local-to-
MRL NSDU lifetime remote-to-
ELR Expected maximum transit
local-to-
ERL Expected maximum transit
remote-to-
R Persistence
AL Local acknowledgement
AR Remote acknowledgement
4.5
TS-user Transport service
TSAP Transport service access
NS-provider Network service
NSAP Network service access
QOS Quality of
14
5 OVERVIEW OF THE TRANSPORT
NOTE - This overview is not exhaustive and has been provided
guidance to the reader of this International Standard
5.1 Service provided by the transport
The protocol specified in this International Standard
the transport service defined in DP 8072.
Information is transferred to and from the TS-user in
transport service primitives listed in table 1.
15
+-------------------------------------------------------------+
| Primitive | Parameter |
|--------------------------------|----------------------------|
|T-CONNECT request | Called Address, |
| indication | Calling Address, |
| | Expedited Data option, |
| | Quality of Service, |
| | TS User-Data. |
|--------------------------------|----------------------------|
|T-CONNECT response | Responding Address, |
| confirm | Quality of Service, |
| | Expedited Data option, |
| | TS User-Data. |
|--------------------------------|----------------------------|
|T-DATA request | TS User-Data. |
| indication | |
|--------------------------------|----------------------------|
|T-EXPEDITED DATA request | TS User-Data. |
| indication | |
|--------------------------------|----------------------------|
|T-DISCONNECT request | TS User-Data. |
|--------------------------------|----------------------------|
|T-DISCONNECT indication | Disconnect reason, |
| | TS User-Data. |
+--------------------------------|----------------------------+
Table 1. Transport service
5.2 Service assumed from the network
The protocol specified in this International Standard assumes
use of the network service defined in DP 8348.
Information is transferred to and from the NS-provider in
network service primitives listed in table 2.
16
+---------------------------------------------------------------+
| Primitives |X/Y| Parameters |X/Y/Z
|----------------------------|---|------------------------|-----|
|N-CONNECT request | X | Called Address, | X |
| indication | X | Calling Address, | X |
| response | X | NS User-Data, | Z |
| confirm | X | QOS parameter set, | X |
| | | Responding address, | Z |
| | | Receipt confirmation | Y |
| | | selection. | |
|----------------------------|---|------------------------|-----|
|N-DATA request | X | NS User-Data, | X |
| indication | X | Confirmation request | Y |
|----------------------------|---|------------------------|-----|
|N-DATA ACKNOWLEDGE | | | |
| request | Y | | |
| indication | Y | | |
|----------------------------|---|------------------------|-----|
|N-EXPEDITED DATA | | | |
| request | Y | NS User-Data. | Y |
| indication | Y | | |
|----------------------------|---|------------------------|-----|
|N-RESET request | X | Originator, | Z |
| indication | X | Reason. | Z |
| response | X | | |
| confirm | X | | |
|----------------------------|---|------------------------|-----|
|N-DISCONNECT request | X | NS User-Data. | Z |
| indication | X | Originator, | Z |
| | | Reason. | Z |
+---------------------------------------------------------------+
Table 2. Network service
17
Key
X - The Transport Protocol assumes that this facility
provided in all networks
Y - The Transport Protocol assumes that this facility
provided in some networks and a mechanism is provided
optionally use the facility
Z - The Transport Protocol does not use this parameter
NOTES
1 - The parameters listed in this table are those in
current network service (first DP 8348).
2 - The way the parameters are exchanged between the
entity and the NS-provider is a local matter
5.3 Functions of the Transport
5.3.1 Overview of
The functions in the Transport Layer are those necessary
bridge the gap between the services available from the
Layer and those to be offered to the TS-users
The functions in the Transport Layer are concerned with
enhancement of quality of service, including aspects of
optimization
These functions are grouped below into those used at all
during a transport connection and those concerned with
establishment, data transfer and release
NOTE - This International Standard does not include the
functions which are under consideration for inclusion in
editions of this standard
a) encryption
18
b) accounting mechanisms
c) status exchanges and monitoring of QOS
d) blocking
e) temporary release of network connections
f) alternative checksum algorithm
5.3.1.1 Functions used at all
The following functions, depending upon the selected class
options, are used at all times during a transport connection
a) transmission of TPDUs (see 6.2 and 6.9);
b) multiplexing and demultiplexing (see 6.15), a
used to share a single network connection between two
more transport connections
c) error detection (see 6.10, 6.13 and 6.17), a function
to detect the loss, corruption, duplication,
or misdelivery of TPDUs
d) error recovery (see 6.12, 6.14, 6.18, 6.19, 6.20, 6.21
6.22), a function used to recover from detected
signalled errors
5.3.1.2 Connection
The purpose of connection establishment is to establish
transport connection between two TS-users. The
functions of the transport layer during this phase must match
TS-users' requested quality of service with the services
by the network layer
19
a) select network service which best matches the
of the TS-user taking into account charges for
services (see 6.5);
b) decide whether to multiplex multiple transport
onto a single network connection (see 6.5);
c) establish the optimum TPDU size (see 6.5);
d) select the functions that will be operational
entering the data transfer phase (see 6.5);
e) map transport addresses onto network addresses
f) provide a means to distinguish between two
transport connections (see 6.5);
g) transport of TS-user data (see 6.5).
5.3.1.3 Data
The purpose of data transfer is to permit duplex transmission
TSDUs between the two TS-users connected by the
connection. This purpose is achieved by means of two-
simultaneous communication and by the following functions,
of which are used or not used in accordance with the result
the selection performed in connection establishment
a) concatenation and separation (see 6.4), a function used
collect several TPDUs into a single NSDU at the
transport entity and to separate the TPDUs at
receiving transport entity
b) segmenting and reassembling (see 6.3), a function used
segment a single data TSDU into multiple TPDUs at
sending transport entity and to reassemble them into
original format at the receiving transport entity
20
c) splitting and recombining (see 6.23), a function
the simultaneous use of two or more network connections
support the same transport connection
d) flow control (see 6.16), a function used to regulate
flow of TPDUs between two transport entities on
transport connection
e) transport connection identification, a means to
identify a transport connection between the pair
transport entities supporting the connection during
lifetime of the transport connection
f) expedited data (see 6.11), a function used to bypass
flow control of normal data TPDU. Expedited data
flow is controlled by separate flow control
g) TSDU delimiting (see 6.3), a function used to
the beginning and ending of a TSDU
5.3.1.4
The purpose of release (see 6.7 and 6.8) is to
disconnection of the transport connection, regardless of
current activity
5.4 Classes and
5.4.1
The functions of the Transport Layer have been organized
classes and options
A class defines a set of functions. Options define
functions within a class which may or may not be used
This International Standard defines five classes of protocol
21
a) Class 0: Simple Class
b) Class 1: Basic Error recovery Class
c) Class 2: Multiplexing Class
d) Class 3: Error Recovery and Multiplexing Class
e) Class 4: Error Detection and Recovery Class
NOTE - Transport connections of classes 2, 3 and 4 may
multiplexed together onto the same network connection
5.4.2
The use of classes and options is negotiated during
establishment. The choice made by the transport entities
depend upon
a) the TS-users' requirements expressed via T-CONNECT
primitives
b) the quality of the available network services
c) the user required service versus cost ratio acceptable
the TS-user
5.4.3 Choice of network
The following list classifies network services in terms
quality with respect to error behavior in relation to
requirements; its main purpose is to provide a basis for
decision regarding which class of transport protocol should
used in conjunction with given network connection
22
a) Type A. Network connection with acceptable residual
rate (for example not signalled by disconnect or reset
and acceptable rate of signalled errors
b) Type B. Network connections with acceptable
error rate (for example not signalled by disconnect
reset) but unacceptable rate of signalled errors
c) Type C. Network connections with unacceptable
error rate
It is assumed that each transport entity is aware of the
of service provided by particular network connections
5.4.4 Characteristics of Class 0
Class 0 provides the simplest type of transport connection and
fully compatible with the CCITT recommendation S.70 for
terminals
Class 0 has been designed to be used with type A
connections
5.4.5 Characteristics of Class 1
Class 1 provides a basic transport connection with
overheads
The main purpose of the class is to recover from
disconnect or reset
Selection of this class is usually based on reliability criteria
Class 1 has been designed to be used with type B
connections
23
5.4.6 Characteristics of Class 2
5.4.6.1
Class 2 provides a way to multiplex several transport
onto a single network connection. This class has been
to be used with type A network connections
5.4.6.2 Use of explicit flow
The objective is to provide flow control to help avoid
at transport-connection-end-points and on the network connection
Typical use is when traffic is heavy and continuous, or
there is intensive multiplexing. Use of flow control
optimize response times and resource utilization
5.4.6.3 Non-use of explicit flow
The objective is to provide a basic transport connection
minimal overheads suitable when explicit disconnection of
transport connection is desirable. The option would typically
used for unsophisticated terminals, and when no multiplexing
network connections is required. Expedited data is
available
5.4.7 Characteristics of Class 3
Class 3 provides the characteristics of Class 2 plus the
to recover from network disconnect or reset. Selection of
class is usually based upon reliability criteria. Class 3
been designed to be used with type B network connections
24
5.4.8 Characteristics of Class 4
Class 4 provides the characteristics of Class 3, plus
capability to detect and recover from errors which occur as
result of the low grade of service available from the NS
provider. The kinds of errors to be detected include:
loss, TPDU delivery out of sequence, TPDU duplication and
corruption. These errors may affect control TPDUs as well
data TPDUs
This class also provides for increased throughput capability
additional resilience against network failure. Class 4 has
designed to be used with type C network connections
5.5 Model of the transport
A transport entity communicates with its TS-users through one
more TSAPs by means of the service primitives as defined by
transport service definition DP 8072. Service primitives
cause or be the result of transport protocol data unit
between the peer transport entities supporting a
connection. These protocol exchanges are effected using
services of the Network Layer as defined by the Network
Definition DP 8348 through one or more NSAPs
Transport connection endpoints are identified in end systems
an internal, implementation dependent, mechanism so that the TS
user and the transport entity can refer to each
connection
25
+------+ +------+
----------| TSAP |------------------------| TSAP |----------
+------+ +------+
| |
+---------------+ +---------------+
| Transport | | Transport |
| entity | | entity |
+---------------+ +---------------+
| |
| |
+------+ +------+
----------| NSAP |------------------------| NSAP |----------
+------+ +------+
| |
+-------------------------------+
Figure 2 . Model of the transport
NOTE - For purpose of illustration, this figure shows only
TSAP and one NSAP for each transport entity. In
instances, more than one TSAP and/or more than one NSAP may
associated with a particular transport entity
26
SECTION TWO. TRANSPORT PROTOCOL
6 ELEMENTS OF
This clause contains elements of procedure which are used in
specification of protocol classes in clauses 7 to 12.
elements are not meaningful on their own
The procedures define the transfer of TPDUs whose structure
coding is specified in clause 13. Transport entities
accept and respond to any TPDU received in a valid NSDU and
issue TPDUs initiating specific elements of procedure
in this clause
NOTE - Where network service primitives and TPDUs and
used are not significant for a particular element of procedure
they have not been included in the specification
6.1 Assignment to network
6.1.1
The procedure is used in all classes to assign
connections to network connections
6.1.2 Network service
The procedure makes use of the following network
primitives
a) N-CONNECT
b) N-DISCONNECT
27
6.1.3
Each transport connection shall be assigned to a
connection. The initiator may assign the transport connection
an existing network connection of which it is the owner or to
new network connection (see Note 1) which it creates for
purpose
The initiator shall not assign or reassign the
connection to an existing network connection if the
class(es) proposed or the class in use for the
connection are incompatible with the current usage of the
connection with respect to multiplexing (see Note 2).
During the resynchronization (see 6.14) and reassignment
failure (see 6.12) procedures, a transport entity may reassign
transport connection to another network connection joining
same NSAPs, provided that it is the owner of the
connection and that the transport connection is assigned to
one network connection at any given time
During the splitting procedure (see 6.23), a transport entity
assign a transport connection to any additional
connection joining the same NSAPs, provided that it is the
of the network connection and that multiplexing is possible
the network connection
The responder becomes aware of the assignment when it
a) a CR TPDU during the connection establishment
(see 6.5);
b) an RJ TPDU or a retransmitted CR or DR TPDU during
resynchronization (see 6.14) and reassignment
failure (see 6.12) procedures;
c) any TPDU when splitting (see 6.23) is used
28
1. When a new network connection is created, the quality
service requested is a local matter, although it
normally be related to the requirements of
connection(s) expected to be assigned to it
2. An existing network connection may also not be
if, for example, the quality of service requested for
transport connection cannot be attained by using
enhancing the network connection
3. A network connection with no transport connection(s
assigned to it, may be available after
establishment, or because all of the transport
previously assigned to it have been released. It
recommended that only the owner of such a
connection should release it. Furthermore, it
recommended that it not be released immediately after
transmission of the final TPDU of a transport connection -
either a DR TPDU in response to CR TPDU or a DC TPDU
response to DR TPDU. An appropriate delay will allow
TPDU concerned to reach the other transport
allowing the freeing of any resources associated with
transport connection concerned
4. After the failure of a network connection,
connections which were previously multiplexed together
be assigned to different network connections, and
versa
6.2 Transport protocol data unit (TPDU)
6.2.1
The TPDU transfer procedure is used in all classes to
transport protocol data units in user data fields of
service primitives
29
6.2.2 Network Service
The procedure uses the following network service primitives
a) N-DATA
b) N-EXPEDITED
6.2.3
The transport protocol data units (TPDUs) defined for
protocol are listed in 4.2.
When the network expedited variant has been selected for class 1,
the transport entities shall transmit and receive ED and EA
as NS-user data parameters of N-EXPEDITED DATA primitives
In all other cases, transport entities shall transmit and
TPDUs as NS-user data parameters of N-DATA primitives
When a TPDU is put into an NS-user data parameter,
significance of the bits within an octet and the order of
within a TPDU shall be as defined in 13.2.
NOTE - TPDUs may be concatenated (see 6.4).
6.3 Segmenting and
6.3.1
The segmenting and reassembling procedure is used in all
to map TSDUs onto TPDUs
30
6.3.2 TPDUs and parameter
The procedure makes use of the following TPDU and parameter
DT TPDUs
- End of TSDU
6.3.3
A transport entity shall map a TSDU on to an ordered sequence
one or more DT TPDUs. This sequence shall not be interrupted
other DT TPDUs on the same transport connection
All DT TPDUs except the last DT TPDU in a sequence greater
one shall have a length of data greater than zero
1. The EOT parameter of a DT TPDU indicates whether or
there are subsequent DT TPDUs in the sequence
2. There is no requirement that the DT TPDUs shall be of
maximum length selected during connection establishment
6.4 Concatenation and
6.4.1
The procedure for concatenation and separation is used in
1, 2, 3 and 4 to convey multiple TPDUs in one NSDU
31
6.4.2
A transport entity may concatenate TPDUs from the same
different transport connections
The set of concatenated TPDUs may contain
a) any number of TPDUs from the following list: AK, EA, RJ
ER, DC TPDUs, provided that these TPDUs come
different transport connections
b) no more than one TPDU from the following list: CR, DR
CC, DT, ED TPDUs; if this TPDU is present, it shall
placed last in the set of concatenated TPDUs
1. The TPDUs within a concatenated set may be
by means of the length indicator parameter
2. The end of a TPDU containing data is indicated by
termination of the NSDU
3. The number of concatenated TPDUs referred to in 6.4.2.a
bounded by the maximum number of transport
which are m