Telecommunications - OSI Protocols - Transport Layer

Transport layer classes

TRANSPORT LAYER STANDARDS

slide tran 4 - Connection request - Variable part

slide tran 6 - Functions within the transport layer

slide tran 7 - Services Provided to the session layer

Example Teletex call


 

1.0 - Introduction

slide tran 0

slide tran 1

Application --> Mail Box File transfer Distributed Database virtual terminal
Presentation
Session
TRANSPORT
Network --> local circuit Packet
Link --> area switching switching
Physical -->

The transport layer hides the beculiarities of the network being used from the layers above.

In the case of a packet switched network the following would be hidden,

  1. Limitations of packet size (by segmenting and concaternation - see below)
  2. limitations of throughput (by multiplexing or splitting)
  3. Loss of data caused by network resets and clears

slide tran 5 -

Recovery from disconnect & reset muliplex several transport onto one network connection error recovery
Class 0 no no no
Class 1 yes no no
Class 2 no yes no
Class 3 yes yes no
Class 4 yes yes yes

Transport layer classes

Class 0 - Simple class

Class 1 - Basic error recovery class

Class 2 - Multiplexing class

Class 3 - Error recovery and multiplexing class

Class 4 - Error detection and recovery class

-----------------------------------------------------------------------------------------------------------


Class 0 - Simple class

  1. Minimum facility
  2. Fully compatible with S.70 Teletex terminals
  3. For use over type A network connections
  4. Only functions for establishment, data transfer with segmenting and error reporting are available.
  5. NO multiplexing, disconnection(closed user network connection cleared), flow control, error recovery, expedited data transfer, user dateline during connection.
  6. Only address and TPDU size parameters are allowed.

Class 1 - Basic error recovery class

Class 2 - Multiplexing class

Class 3 - Error Recovery and multiplexing class

Class 4 - Error detection and recovery class

slide tran2 - jargon


TRANSPORT LAYER STANDARD

ISO 7498 Functions of transport later.

ISO 8072 Transport service definition.

ISO 8073 Transport protocol specification.

S.70 Teletex-network independent basic transport service.


slide tran3 - transport data units


Transport Layer

---------------

Byte: 1 2 3 4 5 6 7 8 9 10
Connection Request LI CR-CDT DST-REF SRC-REF Class Variable User
E x 0 0 Options Part Data
Connection confirm LI CC-CDT DST-REF SRC-REF Class Variable User
D x Options Data
Disconnect Request LI DR DST-REF SRC-REF Reason Variable User
80 Data
Disconnect Confirm LI DC DST-REF SRC-REF Variable Part
C0
Data(Class 0+1) LI DT TPDU-NR Variable part
FO + EOT
Data(Class 2,3+4) DST-REF TPUD-NR User
Data
Extended Format -> TPDU-NR + EOT
Expidited(Class LI ED DST-REF TPUD-NR Variable Part User
Data 1,2,3,4) 10 Data
Extended Format -> ED-TPDU-NR + EOT
Data LI AK-CDT DST-REF YR-TU-NR Variable Part
Acknowledgement 6 x
YR-TU-NR CDT
Extended Format ->
Expediated Data LI EA DST-REF YR-TU-NR Variable part
Acknowledgement 20
Extended Format -> YR-TU-NR
Reject LI RJ-CDT DST-REF YR-TU-NR
5 x
YR-TU-NR CDT
Error LI ER DST-REF REJECT Variable Part
70 Cause

Where:

TPDU = Transport Protocol data unit

LI = Length indicator (1 byte) = Header length (fixed + variable part)

CDT = Credit Allocation (0 in Classes 0 + 1)

TSAP-ID = Transport service access point identifier

DST-REF = Destination reference - reference identifying the transport connection at the remote transport entity

SRC-REF = Source reference - Reference selected by the transport entity initiating to identify the requested transport connection

EOT = End of TSDU mark

TPDU-NR = Data TPDU number

ED-TPDU-NR = Expidited TPDU number

YR-TU-NR = Sequence number response (indicating the next expected TPDU)

YR-EDTU-NR = Expidited TPDU number response

blank


slide tran 4 - Connection request - Variable part

Parameter Code Parameter Length Parameter Value
D1 not defined Transport service access point identifier - called
C2 not defined - calling
C0 01 0D TPDU size - 8192 octets
0C 4096
0B 2048
0A 1024
09 512
08 256
07 128
C4 01 01 version number
C5 user defined security parameters
checksum - always present in class 4
C6 01 Additional option selection
bit 4 use of network expidited in class 1
bit 3 use of receipt conformation in class 1
bit 2 16 bit checksum defined in class 4
bit 1 use of transport expidited data transfer service
C7 n Alternative protocol class(es)
85 2 n Acknowledge time
89 12or24 Throughput
86 3 Residual error rate
87 2 Priority
88 8 Transit delay
8B 2 Reassignment time

blank


slide tran 6 - Functions within the transport layer

  1. mapping transport-address onto network-address;
  2. multiplexing (end-to-end) transport-connections onto network-connections;
  3. establishment and release of transport-connections;
  4. end to end sequence control on individual connections;
  5. end-to-end error detection and any necessary monitoring of the quality of service;
  6. end-to-end error recovery;
  7. end-to-end segmenting, blocking and concatenation;
  8. end-to-end flow control on individual connections;
  9. supervisory functions;
  10. expidited transport-service-data-unit transfer.

blank


slide tran 7 - Services Provided to the session layer

  1. transpoonnection establishment;
  2. data transfer;
  3. transport-connection release.

Establishment phase

Data transfer phase

Release Phase

Primitave Parameters
T - CONNECT request To transport address from transport address
T - CONNECT indication options, quality of service, TS user data.
T - CONNECT reponse responding address, options,
T - CONNECT confirm quality of service, TS user data.
T - DISCONNECT request TS - user data
T - DISCONNECT indication document reason, TS - user data
T - DATA request TS - user data
T - DATA indication TS - user data
T - EXPEDITED DATA TS - user data
T - EXPEDITED DATA TS - user data
indication

Example Teletex call

from network:

xx xx lg lc 0B CE 23 42 12 34 56 78 90 23 42 12 34 56 78 00 02 00 11 C0

from DTE:

call accept

from network:

xx xx yy yy yy 09 E0 00 00 31 31 00 C0 01 07 0D 88

from DTE:

xx xx yy yy yy 08 D0 54 43 41 42 00

from network:

xx xx yy yy yy 02 F0 80 0D 40 01 2E 0A 18 31 32 33 34 35 36 3D 49 44 41

20 20 20 20 20 20 20 20 20 20 20 20 20 20 0B 0E 38 32 2D 30 33 2D 30 30

2D 30 35 2D 31 32 0C 02 30 31 02 06 0D 01 01 0E 01 FE 08 01 01 41 03 4A

01 01 59 34


Call from terminal to network

from host:

xx xx 14 00 0B 0E 99 99 88 88 00 02

from network:

xx xx 14 00 OF 0E 00

from terminal:

xx xx 14 00 yy 06 E0 00 00 00 01 00

from network:

xx xx 14 00 yy 09 D0 00 01 31 31 00 C0 01 07

from terminal:

xx xx 14 00 yy 02 F0 80 0E 34 01 2A 09 18 32 33 34 32 2D 31 32 33 34 35

36 30 32 2D 31 32 33 3D 41 42 43 44 0B 0E 38 34 2D 30 33 2D 30 35 2D 31

31 3A 31 39 08 01 01 41 03 4A 01 01

Example Teletex call

--------------------

from network:

xx xx lg lc 0B CE 23 42 12 34 56 78 90 23 42 12 34 56 78 00 02 00 11 C0

from DTE:

call accept

from network:

xx xx yy yy yy 09 E0 00 00 31 31 00 C0 01 07 0D 88

from DTE:

---------

xx xx yy y yy 08 D0 54 43 41 42 00

from network:

-------------

xx xx

yy yy yy

02 F0 80 0D 40 01 2E 0A 18 31 32 33 34 35 36 3D 49 44 41

(123456=IDA)

20 20 20 20 20 20 20 20 20 20 20 20 20 20 0B 0E 38 32 2D 30 33 2D 30 30

(82-03-00)

2D 30 35 2D 31 32 0C 02 30 31 02 06 0D 01 01 0E 01 FE 08 01 01 41 03 4A

(-0512 01)

01 01 59 34


Call from terminal to network

-----------------------------

from host:

----------

xx xx 14 00 0B 0E 99 99 88 88 00 02

from network:

-------------

xx xx 14 00 OF 0E 00

from terminal:

--------------

xx xx 14 00 yy 06 E0 00 00 00 01 00

from network:

-------------

xx xx 14 00 yy 09 D0 00 01 31 31 00 C0 01 07

from terminal:

--------------

xx xx 14 00 yy 02 F0 80 0E 34 01 2A 09 18 32 33 34 32 2D 31 32 33 34 35

36 30 32 2D 31 32 33 3D 41 42 43 44 0B 0E 38 34 2D 30 33 2D 30 35 2D 31

31 3A 31 39 08 01 01 41 03 4A 01 01


metadata block
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