1

Basic ISDN CourseIntroduction

Basic ISDN CourseIntroduction

2

OSI, 7 Layer ModelOSI, 7 Layer Model

Application

Presentation

Session

Transport

Network

Datalink

Physical

Layer 7G4 terminal characteristics

Layer 6Coding method, MMR JBIG

Layer 5G4 Protocol

Layer 4Block length

Layer 3Packet length

Layer 2HDLC Establishment

Layer 1Connector, electrical char.

3

ISDN OutlineISDN Outline

Layer Layer Name Dch Bch

7

6

5

4

3

2

1

Application Layer

Presentation Layer

G4 Terminal Only

Session Layer

Transport Layer

Network Layer

Data Link Layer

Physical Layer

Call Control

Terminal Distinguished byError-Free High-Quality Data

Wiring format, ElectricCharacteristics

Image Data

Paper Size, Resolution QualityNegotiation

Decided by TransportationHead

Packet Control

Error-Free High-Quality Data

OSI 7 layer model Uses

Not used

4

Layer ImplementationLayer Implementation

5

Layer 1 FunctionLayer 1 Function

The physical layer determines the physical transmission characteristics of a node to

node link.It specifies the mechanical and electrical

conditions, such as the voltage levels and the signalling conventions to provide the

transmission characteristics like: the timing of the signals and connector specifications

for sending the stream of data over the physical transmission medium

6

Layer 2 FunctionLayer 2 Function

The data-link layer takes the layer 1 information stream and applies the

necessary functions to ensure error-free transmission at every link in the

transmission path. Detection and correction of errors is performed by the

layer 2 protocol at each node to node link.Layer 2 also includes the specifications for

the HDLC procedures.

7

Layer 3 FunctionLayer 3 Function

The network layer defines how the total communication route is assembled using the error-protected links provided by layer

2. Layer 3 uses a signalling protocol to determine what path to take through the

network to transfer the information.

8

Layer 4 FunctionLayer 4 Function

The transport layer guarantees data communication between two point in a

network not using a fixed communication line.

9

Layer 5 FunctionLayer 5 Function

The session layer co-ordinates the communication between two terminals and

controls the right way for transmitting.For a G4 facsimile, layer 5 would check the

transmission for every page unit.

10

Layer 6 FunctionLayer 6 Function

The presentation layer determines the structure of the data to be handled between

the application layers involved.In other words, layer 6 determines the

language ( or in data communications, the codes) in which the transmission will take

place. For a G4 facsimile, layer 6 would set up the

transmission for coded picture data.

11

Layer 7 FunctionLayer 7 Function

The application layer provides the general means for networks to use the steps

through ISO. The purpose of using a G4 facsimile is to

transmit and receive picture images. Layer 7 provides the constants for the

communications equipment, such as the size of the document and the scanning

resolution.

12

Overview of G4 Protocol Recommendations

Overview of G4 Protocol Recommendations

13

ITU-T T.563ITU-T T.563

Terminal characteristics for Group 4 facsimile apparatus

14

G4 Terminal CharacteristicsG4 Terminal Characteristics

Group 4 facsimile apparatus is used mainly on Public Data Networks (PDN) including circuit-switched, packet-switched, and the Integrated Services Digital Network (ISDN).

The procedures used with Group 4 facsimile apparatus enable it to transmit and reproduce image-coded information essentially without transmission errors.

Group 4 facsimile apparatus has the means for reducing the redundant information in facsimile signals prior to transmission.

The basic image type of the Group 4 facsimile apparatus is black and white. Continuous tone grey scale and colour image type of G4 facsimile apparatus are optional.

15

Differences Between G3 & G4 Terminal

Differences Between G3 & G4 Terminal

16

G4 Facsimile Classes 1G4 Facsimile Classes 1

17

G4 Facsimile Classes 2G4 Facsimile Classes 2

18

Basic Terminal Capabilities for G4 Facsimile

Basic Terminal Capabilities for G4 Facsimile

19

Scope of Recommendation T.563Scope of Recommendation T.563The rules to be followed in the Group 4 facsimile services are defined in Recommendation F.184.

The Group 4 facsimile coding scheme and facsimile control functions are defined in Recommendations T.6, T.81 and T.82.

Group 4 facsimile apparatus communicates with unique procedures that are described as follows:

a) the interface to the physical network is defined in this Recommendation;

b) the transport end-to-end control procedure is defined in Recommendation T.70;

c) Group 4 facsimile control procedures are defined in Recommendation T.62;

d) Group 4 facsimile communication application profile is defined in Recommendation T.521;

e) Group 4 facsimile document application profile is defined in Recommendation T.503.

For the continuous tone colour image, the continuous tone colour representation method for G4 facsimile is defined in Recommendation T.42.

20

G4 Guaranteed Reproducible AreaG4 Guaranteed Reproducible Area

T0810790-92/d02210 mm

297

mm

196.6 mm

277.

23 m

m11

.54

mm

4.23

mm

4.23

mm

8.23

mm

Call Identification Line (Note 1)

Call Identification Line (Note 1)

Figure A.1/T.563 – Guaranteed reproducible area for Group 4 apparatus for use onfacsimile services referring to ISO A4 paper size

NOTE 1 – The Call Identification Line is printed either on top or below the guaranteed reproducible area.

NOTE 2 – Paper characteristics (i.e. weight) are important parameters. Lightweight paper may cause additional paper handling errors and may result in a reduced guaranteed reproducible area.NOTE 3 – Sheet feed mechanisms may reduce the guaranteed reproducible area.

NOTE 4 – All calculations were done using worst case values. Using nominal values increases the reproducible area.

NOTE 5 – The exact horizontal position of this area within the ISO A4 paper size as well as sizes larger than the above are subject to national recommendations and/or definitions.

21

Network Related RequirementsNetwork Related Requirements

Integrated Services Digital Network (ISDN)

The operations and rules of Group 4 facsimile apparatus on the ISDN are defined in Recommendation T.90. On the ISDN, Group 3 and Group 4 facsimile functions can be implemented in Group 4 facsimile. The operations and rules of the terminal having Group 3 and Group 4 facsimile functions are described in the Appendix I/T.90.

22

Lower layer OverviewLower layer Overview

23

Recommendation Overview Notes 1Recommendation Overview Notes 1NOTES1 The X.25 network layer procedure is introduced to ease interworking with PSPDNs.2 The establishing of the network connection is performed by two-stage selection: the first using normal telephone procedures and the second using X.25 call control procedures.3 For terminals connected to PSTN accessing PSPDN, the procedures in Note 2 apply.4 Recommendation T.71 defines a half-duplex link access procedure, based on Recommendation X.75 for single link operation.5 The link layer procedures are in accordance with Recommendation X. 75 for single link operation.

24

Recommendation Overview Notes 2Recommendation Overview Notes 2

6 In all cases of interworking including interworking between terminals connected to the same type of network or to different types of networks (i.e. CSPDN, PSPDN, PSTN), this transport layer procedure is executed peer-to-peer between the communicating terminals.7 For terminals connected to CSPDNs, no function is needed in the network layer in the data transfer phase as indicated. However, in order to facilitate interworking with PSPDNs a minimum network layer is introduced.8 The modem may also be integrated within the terminal and in such cases Recommendation V. 24 need not apply.9 For automatic calling and/or answering, Recommendation V.25 may be applicable.

25

Network Layer Procedure 1Network Layer Procedure 1Recommendation X.25 Virtual Call procedures apply. However, the following points should be noted when using this transport protocol:a) The qualifier bit in data packets should always be set to 0.b) The delivery confirmation bits in all packets should be set to 0.c) The terminal should not send an interrupt request packet.d) Normal X.25 reset procedures will apply.e) Each control block or data block of the transport layer shall be carried in a complete data packet sequence.

26

Network Layer Procedure 2Network Layer Procedure 2

f) The terminal should not send a DTE REJ packet.g) Terminals shall use a specific protocol identifier within call request/incoming call packets for the Group 4 facsimile apparatus. This identifier is represented by the first octet of the call user data field (remaining octets, if any, should be ignored) as shown below:

bit 87654321octet 1 00000010

h) Terminals shall not use the fast select facility.

27

Link Layer ProcedureLink Layer Procedure

Depending on the service provided by the physical layer, the link layer procedures over a single physical circuit between two terminals have to cater for a half-duplex or full-duplex transmission facility to provide a full-duplex service to the network layer. For full-duplex physical layer service, the link layer procedure shall conform to the Link Access Procedure, for single link operation. For addressing assignments and the system parameters see the next slide. For half-duplex physical layer service the link layer procedure is a half-duplex Link Access Procedure, for single link operation.

28

ITU-T T.90ITU-T T.90

CHARACTERISTICS AND PROTOCOLS FOR TERMINALS FOR TELEMATIC

SERVICES IN ISDN

29

Scope of the RecommendationScope of the Recommendation

The Integrated services digital network (ISDN) supports a wide range of voice and non-voice services and applications in the same network via a multipurpose user-network interface.

This Recommendation describes the requirements for telematic terminals, developed for ISDN application, and connected to an ISDN via an I-Series interface.

30

Bearer CapabilitiesBearer Capabilities

This Recommendation is based on the use of bearer capabilities defined for the ISDN, using B-channels for the information transfer and virtual circuit connection control and the D-channel for the connection control.

Protocol architecture

This Recommendation provides the application rules for other CCITT Recommendations and ISO standards aiming at end-to-end (DTE-DTE) communication through the network as well as DTE-DCE interconnection and support of OSI-network service.

31

ISDN B-Channel Circuit-switched Mode

ISDN B-Channel Circuit-switched Mode

For this mode the circuit-switched 64 kbit/s unrestricted information transfer capability shall be used.

32

Protocol SetProtocol Set

T080570 1-91

< D -channel > < B-channel >

Q.931

Q.921(LAPD)

Physical connectioncontrol

Virtual connectioncontrol and

information transfer

ISO/CEI 8208 (Note 3)

ISO/CEI 7776 DTE/D TE operation (Note 2)

OSI layer

3

2

1

F IG U R E 1 /T .9 0

I.430/I.431 (Note 1)

Note 1 – S ee § 2 .2 .1 .

Note 3 – D T E -D T E c o n n ec tio n is sp e c if ied o n th e b a sis o f IS O /IE C 8 2 0 8 (M arch 1 9 9 0 ) as d e scr ib ed in § 2 .2 .5 .In case of the completion of LLC negotiation, the T.70 NL protocol (CSPDN minimum header, Recommenda-tion T.70, § 3.3) may optionally be supported in addition to the ISO/CEI 8208 and used on a per-call-basis. In case of the failure or the absence of LLC negotiation, ISO/CEI 8208 protocol shall be used. For further information see Appendix II.

Note 2 – Fu ll-d u p lex sin g le l in k p ro c ed u res a re d ef in ed as d es cri b ed in § 2 .2 .3 . F o r se rv ice d efin it io n s an d s ta te transition diagrams for the data link layer wihtin the B-channel, see Appendix III.

33

Application RulesApplication Rules

Layer 1 – Physical layer interface characteristics

The physical interface characteristics shall be in accordance with the I-Series Recommendations: I.430 (Basic user-network interface, layer 1 specifications. This layer provides full duplex transmission capability.

Layer 2 – D-channel connection control phase

Recommendation Q.921 shall apply.

Layer 2 – B-channel link layer procedure

The link layer procedure shall consist of a fully symmetrical HDLC procedure.

34

Address Procedure 1Address Procedure 1

bit

Address1 2 3 4 5 6 7 8

A 1 1 0 0 0 0 0 0

B 1 0 0 0 0 0 0 0

Note – The terminal will discard all frames received with an address other than A and B.

The following describes the application of the link addressing procedures. Link addresses (A and B) shall be assigned dynamically on a per-call-basis according to the following rules:

a) the calling terminal shall take address A;

b) the called terminal shall take address B;

c) commands and responses shall be transferred as shown on next slide;

d) A and B addresses are coded as follows:

35

Address Procedure 2Address Procedure 2

T0805710 -90

Callingterm inal

A

Calledterm inal

B

Commands (B)

C ommands (A)

Responses (B)

Responses (A)

F IG U R E 2 /T .9 0

36

Use of Low Layer Compatibility Codes

Use of Low Layer Compatibility Codes

8

0/1

0/1

0/1

0/1

0/1

1

1

T0807230-91

7 6 5 4 3 2 1

1 0 0 0 1

0 0 0 0 0

0 0 1 1 1

0 0 0 0 0

1 0

00 0

1 1

ext

ext

ext

ext

ext

ext

ext

User information layer 2 protocol(ISO/CEI 7776 – DTE-D TE operation)

U ser inform ation layer 3 protocol(ISO/CEI 8208)

Q.933 use(Q.933 not used)

Layer 2 ident.

Layer 3 ident.

Packet window size

Packet size

Value of k parameter

ModeSpare

SpareMode

Spare

Octets6

6a (Note 1)

6b (Note 1)

7a (Note 2)

7b (Note 2)

7c (Note 2)

7

F IG U R E 3 /T .9 0

E n cod in g o f lo w la y er co m p a tib ility in fo rm a tio n e lem en t

Note 1 – If octet 6b is present then octet 6a shall also be present.

Note 2 – If octet 7b is present then octet 7a shall also be present. If octet 7c is present then octets 7a and 7b shall also be present.For values not fixed in this Figure, see Table 1/T.90.

37

Use of HLC CodesUse of HLC CodesAn example of such a scheme is illustrated in Table 2/T.90.

TABLE 2/T.90

Use of HLC codes by teletex and group 4 facsimile terminals

Telematic serviceHLC codes

terminalsSent from calling

terminals (Notes 2 and 3)Accepted by receiving

terminals (Note 4)

Basic teletex Basic teletex Basic teletex

Teletex mixed mode Basic teletexMixed mode (Note 1)

Basic teletexMixed mode

Group 4 facsimileclass 1

Group 4 facsimile Group 4 facsimile

Group 4 facsimileclass 2

Group 4 facsimile Group 4 facsimileMixed modeBasic teletex

Group 4 facsimileclass 3

Group 4 facsimileMixed modeBasic teletex (Note 1)

Group 4 facsimileMixed modeBasic teletex

Note 1 – In case that the calling terminal is teletex mixed mode or group 4 facsimile class 3, onlyone element is to be sent depending on originating document type.

Note 2 – For multi-service telematic terminals sending more than one document in the same call,the HLC indicates functionality required for that call.

Note 3 – When the calling terminal only wishes to receive a document from a called terminal(polling), HLC IE indicates the preferred functionality of the calling terminals.

Note 4 – Appendix I provides additional information in order to cater for cases where calls forfacsimile equipment are incoming from networks not able to convey HLC information.

38

Layer 3 B-Channel Connection Control 1

Layer 3 B-Channel Connection Control 1

The following shall be noted when using this protocol:a) calling DTE shall send a RESTART REQUEST packet, begin the restart procedure, and establish virtual circuits. b) the qualifier bit in data packets shall always be set to “0” for teletex and group 4 facsimile and may be set to “0” or “1” for videotex;c) the delivery confirmation bits in all packets should be set to “0”;d) normal X.25 reset procedures shall apply;e) each control block or data block of the transport layer shall be carried in a complete data packet sequence;

f) the terminal should not send a DTE REJECT packet;

39

Layer 3 B-Channel Connection Control 2

Layer 3 B-Channel Connection Control 2

g) in case of group 4 facsimile and teletex, terminals shall use a specific protocol identifier within CALL REQUEST/INCOMING CALL packets. This identifier is represented by the first octet of the call user data field as shown below:bit 8 7 6 5 4 3 2 1octet 0 0 0 0 0 0 1 0

Other values are for further study;h) out-of-band negotiation of layer 3 modulo may be performed through the use of the LLC information element;

i) it is recommended that the value chosen for modulo for layer 3 shall be the same as the modulo for layer 2.

40

ISDN B-Channel-packet Switched Mode

ISDN B-Channel-packet Switched Mode

The protocol set applicable to the packet-switched mode (PS mode) is shown below.

T0805 721-91

F IG U R E 4 /T .9 0

Q.931

Q.921(LAPD)

X.25 PLP

X.25 LAPB

< D-channel > < B-channel >

I.430/I.431 (N ote)

N ote – S ee § 2 .2 .1 .

3

2

1

OSI layerAccess connection

control

Virtual connectioncontrol and

inform ation transfer

41

Additional X.25 Optional User Facilities

Additional X.25 Optional User FacilitiesCategories of additional functions

On-line facility registrationFlow control parameter negotiation

Service oriented user facilities (network based)Closed User Groups (CUG) selectionCUG with outgoing access selectionReverse chargingNetwork user identificationCharging informationRecognised private operating agency (RPOA) selectionCall redirection notificationCalled line address modified notification

Note – D-bit modification is not supported.

42

Interaction between D and B-ChannelInteraction between D and B-Channel

Communication between the D-channel and B-channel is not synchronised in relation to each other by the ISDN and therefore information exchange via these channels can be accomplished independently and simultaneously.

As a consequence of this, messages sent in the D-channel and B-channel in a distinct relationship to each other may be received in a different order.

In order to achieve an orderly operation of the protocols in all telematic equipment, it is necessary to have an additional procedure to maintain the timing relationship.

This model, architecture, and primitives of this additional procedure is left for further study.

43

Supplementary informationSupplementary information

If the ISDN provides date/time information in the CONNECT message to the ISDN telematic terminal, this information shall take precedence over any other local available corresponding information (at least for call identification line).

44

SynchronisationSynchronisationThe ISDN guarantees that the B-channel will be open for data traffic as soon as the CONNECT message has been received at the terminals. However, due to propagation delay the two CONNECT messages may not arrive at each terminal at the same time.

Therefore the following procedure shall be used.

The calling side and called side follow the sequence (see Note 3):

1) the calling side and called side send “1”-bits until notified of B-channel establishment;

2) the called side sends CONNECT signal to the network when it activates the receiver circuit. The calling side activates the receiver circuit when CONNECT signal arrives from the network;

3) the calling side and called side send flags to the peer entity (see Note 1);

4) the calling side and called side start communication, i.e. the calling side sends SABM/SABME the called side (see Note 2) and the called side responds UA command to the calling side when SABM/SABME and arrives from the calling side.

45

Synchronisation NotesSynchronisation Notes

Note 1 – If possible, the following sequence may be useful for reliable synchronisation:

a) the calling side sends at least 64 concatenated flags aligned so that two adjacent “0”s occur between each string of “1”s until the first flag arrives from the called side and the called side sends at least 64 concatenated flags of the same type until SABM/SABME command arrives from the calling side;

b) the calling side and called side consider the peer entity as active when the first flag arrives from the peer entity.

Note 2 – Flag detection before sending SABM/SABME may make more reliable synchronisation.

Note 3 – Terminal adapter connected by the existing telematic terminal should support the above sequence.

The sequence diagram describing the operation of the calling side and called side is shown in Figure 5/T.90.

46

Layer 2 SynchronisationLayer 2 Synchronisation

T0810870-92/d05

SA B ME

SA BM E

UA

U A

I

SA BM /S AB ME

UA

F IG U R E 5 /T .9 0

T h e seq u en ce o f sy n ch ro n iza t io n o n la y er 2

I (SETUP)

I (CALL PROC EEDIN G)

I (ALERTING)

I (C ONN ECT)

I (CON NEC TACKN OW LED GE)

(N ote 2)SEQUEN CE OF FLAGS

SEQUEN CE OF FLAGS

I (C ONNECTACKNO W LEDGE)

I (CO NNECT)

I (ALERTING)

U I (SETUP)

Sequence of "1" b itsSequence of "1" bits

Callestablishment

Ready tocommunicate

Callestablishment

R eady tocomm unicate

C alling side Netw ork Called side

N ote 1 –

N ote 2 – T h e p ro visio n o f th e C O N N E C T A C K N O W L E D G E sign a l is o p tio n a l.

D – ch an n e l s ig n a ls

B – ch an n e l s ig n a ls

47

ISDN D-Channel Connection PhaseISDN D-Channel Connection Phase

48

ISDN D-Channel Clearing PhaseISDN D-Channel Clearing Phase

49

B-Channel Control & Information Transfer

B-Channel Control & Information Transfer