ISDN Basics

1ISDN Strategy - June 2001 - Bertrand Pinel

ISDN Training / ISDN Basics


Introduction to ISDN ISDN Network Architecture ISDN Protocols ISDN Customer Premises equipment Supplementary services Corporate Networks

ISDN Training / ISDN Basics


Introduction to ISDN

� Definition� ISDN Story� Benefits� ISDN Interfaces


Introduction to ISDN / Definition

Integrated

ISDN is a global network for data and voice transfer

ServicesISDN is a wide offer of services (Bearer services,

Teleservices,Supplementary services)

DigitalISDN offers end to end digital integrity to the end-users

Network



Transmission capabilities provided by the network

• 64 kbits/s for data transmission• speech • 3.1 KHz audio• Packet switched data (X.25)

End to end Application (terminal equipment functions)

• Telephone• Videotex• Fax group 3 and group 4• videotext ......

Value Added services to the ISDN core services

• additional network functions • subscriber network information • filteringCUG, UUS, HOLD, CLI, CF, TP, AOC ...



PSTN

PSPDN

TELEX

Phone

Fax G3

Host Computer

Data Terminal

Telex

Leased Line

Analog Interface



Phone

Fax G3

Host Computer

Data Terminal

Telex

NT1 ISDN001101110110

NT1: Network Termination


• 1937: Pulse Code Modulation (voice sampling and digitalization theory)• 1960: Introduction of digital transmission between the exchanges (PCM30)• 1971: First work of CCITT (ITU) on Integrated Services (digital) Network• 1970/1980: Introduction of digital exchanges in most of operator networks. • 1984-1988: CCITT defines the digitalization of the subscriber line in its “Red Book” and Blue Book• 1984-1987: first trials on different countries (UK, France, US and Germany). Lack of standardization => Creation of national

standards

• 1988: European Telecommunications Standards Institute is created and helps at ISDN standardization process

Introduction to ISDN / ISDN story



April 1989: a Memorandum of Understanding (MoU) is signed by 26 operators from 20 European countries.

Definition of common user/network interfaces (BRA and PRA) Agreement on services and supplementary services by each signatory Opening of the following services based on common standard before 1994

Bearer services:- unrestricted 64 kbits/s circuit mode- 3.1 kHz audio circuit mode

Supplementary services:- Calling Line Identification Presentation and Restriction (CLIP/CLIR)- Multiple Subscriber Numbers (MSN)- Direct Dialling In (DDI)- Terminal Portability (TP)



1990: Definition of a new standard for the support of international ISDN and based on CCITT SS7. This protocol is called TUP+ (Transfer User Part).

1991: Definition of ISDN user part (ISUP) for the support of supplementary services on international ISDN.

1990-1996: Definition of ETSI supplementary services (EDSS1 protocol).

1993: 14 countries offer international ISDN.

1998: 59 operators in 50 countries offer international ISDN.


ITU-T (CCITT): International Telecommunication Union - Telecommunication

(I series for ISDN)

ETSI: European Telecommunications Standards Institute (ETS)

ISO: International Standardization Organisation (protocol definition)



Introduction to ISDN / Benefits

Re-use of existing local loop for BRA High Speed Transmission (144 kbit/s to 2.048 Mbit/s) Digital Quality (reliability and safety) Services Integration on a standardized interface Enhanced signalling for a larger services offer International standardization Simple wiring


Introduction to ISDN / ISDN interfaces

Access to ISDN thanks to standardized user interfaces Based on digital technology and switching

Two main user-network interfaces

- Basic Rate Interface (or Access)

- Primary Rate Interface (or Access)


• Basic Rate Interface or Access / BRA (2B+D S0/T0 192 Kbps)

– Two B channels for user voice or data information (64 Kbps) in circuit mode• provide end-to-end digital transmission service.

– One D channel reserved for control, signalling data and low rate application (X.25/D in packet mode) at 16 Kbps.

DB1

B2

D Channel 16 Kbit/s signalling, low transfer rate data

B Channel 64 Kbit/s speech , text, data, pictures



• Primary Rate Access / PRA 30B+D ( S2 2.048 Mbps)

– 30 B channels (timeslots) in Europe and 23 B channels in USA and Japon for user voice or data information (64 Kbps)

• provide end-to-end transmission service.

• Agregation of B channels on demand (384, 1920 kbps)

– One D channel for signalling, control and packet data (TS=16 at 64 Kbps)

23 to 30 B channels

D

B1

B2

D Channel 64 Kbit/s signalling, low transfer rate data



B...

B30B Channel 64 Kbit/s speech , text, data, pictures



ISDN Network Architecture

¨ Local loop / Digital subscriber Line / Reference points¨ U interface¨ Basic Rate Interface (Access)¨ Primary Rate Interface (Access)¨ Bus configuration (PP, PMP)



Terminal Network

Access

Circuit

Exchange

Packets

Exchange

channelsignalling

Network

AccessTerminal

Higherlevel

Functions

ISDN

S/TS/T

user-networksignalling

user-user

signalling

SS7

ISDNinterface

ISDNinterface



R S T U V

or

P.C. PABXTerminal

NT2 NT1

Reference Points

LT ET

TE1

TATE2

Local Exchange

2 wire

PUBLIC NETWORKPRIVATE NETWORK

PUBLIC NETWORK (U.S)

TE1 Terminal equipment type 1 (ISDN compliant)

TE2 Terminal equipment type 2 (non ISDN compliant)

TA Terminal Adapter

NT1 Network termination 1 NT2 Network termination 2 (Optional)

LT Line Termination ET Exchange Termination

ISDN

4 wire



Customer Premises

NT1 Repeater LT Exchange

Operator Premises(Local Exchange)

U Interface U InterfaceS/T Interface2 wire

DigitalSubscriberLine (copper pairs)

4 wire



- Two line codes:

• 2B1Q: the most spread: used in all European countries (except Germany) and in USAPrinciple: Converts Two binary digits into one quaternary element

Binary 2B1Q00 -301 -110 +311 +1

• 4B3T: Only used in Germany Principle: Converts Four binary digits into three ternary digits (3 levels)

- Only one equipment can be connected to the U interface (Point to Point configuration)- U interface is only standardized at Basic Rate Access

+3

+1

-1

-3



2 B Channels

D Channel

Bit timing

Octet timing

Frame alignment

Activation

Deactivation

Power feeding

Operations and maintenance

NT1 LT



All the D and B channels information plus additional information for maintenance

CL12 * (2B+D) = 216 bitsFW/IFW

18 bits 216 bits 6 bits

1,5 ms (160 Kbits/s)

FW : Frame Word IFW: Inverted Frame Word

CL: Channel for operation and maintenance



Embedded Operation Channel (EOC): specific operations between the network andNT1 for maintenance (loop commands, sending of corrupted information ...)

Activation and deactivation commands and indicators (ACT, DEA, SAI, UOA)

NT1 Power feeding status

Cyclic Redundancy Check: for transmission error detection

Far End Block Error (FEBE)


- Signalling and data informations are separated in ISDN protocol.

- The D channel supports signalling for all equipments connected on the BRA Access (up to eight).

- BRA allows the customer to set-up two communications at the same time.

- Mainly used by small compagnies and residential market (Small Office/Home Office)

BRA : Point to Point and Point to Multi-point configurations

Basic Rate Access installation

Phone

Fax G3

Computer

NT1 ISDN

T0TA

2 wire4 wireNT2

S0

2 B+D


Primary Rate Access installationfor large facilities

Telephony network

Computer Network

ISDN

PRA access are mainly used for PBX (Private Branch Exchange) connection and company needs

PRA = Point to Point configurationLayer 1 is permanent

NT1Server

NT2 (PBX)

30 B+D

T2



Primary Rate Access installationin Point to Point configuration

ET

T2

NT1

PBX

NT2

LT

S U2

LOCALEXCHANGE

V

Point to Point Link

30B + D



Basic Rate Access installationin Point to Point configuration

ET

S/T

NT1 LT

U

LOCALEXCHANGE

Point to Point Link

2B + D



Basic Rate Access installationin Point to Multi-Point configuration

ET

S/T

NT1 LT

U

LOCALEXCHANGE

Point to Multi-Point Link

2B + D


OSI Model D-Channel Protocol Protocols over the B channel (PPP/MLP, IP, TCP, HTTP)


ISDN Protocols / OSI Model

Open System Interconnection defined by ISO (International Standard Organisation)

OSI model defines system interconnection thanks to 7 different layers Each Layer provides a specific service to the upper layer ISDN User Network interface is based on the OSI reference model



DATA LAYER

PHYSICAL LAYER

NETWORK LAYER

TRANSPORT LAYER

SESSION LAYER

PRESENTATION LAYER

APPLICATION LAYER

Signal characteristics, pulse amplitude, line coding, transmission rates connectors ...

Procedure for link establishment, digits assembling into frames with error detection and correction. High Level Data Link Control

Basic Call Control: routing (address solving), call establishment and release ...

Use

r L

ayer

sL

ow

Lay

ers

Layer specific to each application (User interface etc ...)

End to end or terminal to terminal layer (Rates adaptation ...)

Session management (opening and closing session)...

Data formatting



ISDND Channel D Channel

B ChannelB Channel

NTNT

LT LT

User/Network

User to User Signalling

Network signaling (SS7)

User A User B

User/Network

ISDN OSI Model Application

Application 7

Presentation 6

Session 5

Transport 4

Network 3

Data Link 2

Physical 1


ISDN Protocols / D-Channel Protocol

• Breaks up into four areas: mechanical, electrical, functional and procedural and provides a mechanism by which a terminal can transmit data to the network

• Conforms to CCITT Recommendation I.430

• Multi-point bus: up to 8 terminals may be connected

• Power feeding: terminals are generally powered by the NT

• Activation/Deactivation procedure to save energy. The bus is activated only when a communication has to be established.



B1Channel B2Channel B1Channel B2ChannelD D D DM M M M M M M M M M M M

8 bits 8 bits 8 bits 8 bits

M Multiframing Bit for managment and maintenance

D

B1Channel

D Channel Bit

B Channel Bits

250 µs (48 bits - 192 Kbits/s)



4 Wire S/T bus:

• Two wire: emission• Two wire: reception

• BRA: Power supply (PS1) is provided in phantom mode over those wires.

Optional at BRA:

• Two wires: optional power supply (PS2)• Two wires: used for providing power supply to other terminal



TE NTINFO 0

INFO 0

INFO 1

INFO 2

INFO 3

INFO 4



• Conforms to CCITT Recommendation I.431• Point-to-point link• Permanent Layer 1• Frames conform to G.703 and G.704 Recommendations



Synch.

8 bits

125 µs (256 bits - 2.048 Mbits/s)

Timeslot 0

D Channel

8 bits

Timeslot 16

B Channel

8 bits

Timeslot 2

B Channel

8 bits

Timeslot 31

B Channel

8 bits

Timeslot 30

B Channel

8 bits

Timeslot 1



Based on CCITT Q.921 recommandation• Establishes, maintains and releases the data link connection and provides error-free transmission using error detection and flow control.• Ensures that messages are delivered in the correct order without loss or duplication.• Based on High Level Data Link procedure for the D channel (LAPD)• acts as a carrier for LAYER 3 information• same procedure for both PRA and BRA interfaces



0 1 1 1 1 1 1 0

S A P I C/R EA0

TEI EA1

N(S)

N(R)

LAYER 3 Information

FCS byte 1

FCS byte 2

0 1 1 1 1 1 1 0

OPENING FLAG

CLOSING FLAG

Frame Check Sequence

Next Frame to send

Next Frame to receive

Service Access Point Identifier

Terminal Endpoint identifier


Two main information:

Service Access Point Identifier (SAPI): identify the service for which the signalling frame is intended for.

Terminal endpoint identifier (TEI): is a specific information which identifies clearlyeach terminal connected on the bus and allows the network to manage several LAPs at the same time.


SAPI Values

0 Call Control Procedure16 Packet Communication63 Layer 2 Management procedure


Layer 1


– SAPI gives access to the Layer 3

TEI-Management

X.25data

Lay

er 2

Lay

er 3

X.25 -Protocol

SAPI 0 SAPI 16SAPI 63

L3 ISDNProtocol

Layer 2 data frames



TEI can be set by the user or automatically by the network

TEI ranges

0-63 Non-automatic TEI assignments64-126 Automatic TEI assignments127 Global TEI for broadcast

Automatic assignment is a specific negociation phase between the network and the terminal which occurs each time the terminal whishes to establish a LAP.



S/T

NT1

U

Point to Multi-Point Link

2B + D

TEI 64

TEI 65

TEI 66 TEI 127

TEI 64





INFORMATION

SUPERVISORY

UNUMBERED

For the upper layer accordingto the SAPI value.

SABME, UA, DISC, DM, FRMR

RR, RNR, REJ

IFRAME

Flow control and supervisoryfunctions.

Transfer and control function(LAP establishment and release).

exception : the Unumbered Information frames contain information mainly for broadcast



TE NT

ID.REQUEST

ID.ASSIGN

SABME

UA



Establishment and control of connexions between the exchange and the terminal.

Conveyed inside Layer 2 frames

Two parts:

Basic call control based on CCITT Q.931 (circuit-switched calls) Supplementary services based on CCITT Q.932 and further described in ETSI standards for DSS1 protocol



8 7 6 5 4 3 2 1

Protocol Discriminator 0 0 0 0 1 0 0 0

0 0 0 0 Call Ref. Lg

Call Reference Value

0 Message Type

Information Elements ( CHI, BC, Add, Cause..)

Byte 1

Byte 2

Byte 3

Byte 4

.....

Q.931 Signalling message structure

Identifies messages relating to a call or a facilityregistration

Identifies the protocol08 for protocol compliant with Q.931 standard

Describes the function of the message

Other information required to perform the functionand defined in the message format



Group 1 Call establishment messages

0000001 ALERTing Calling subscriber

0000010 CALL PROCeeding Establishing of call

0000111 CONNECT Connection

0001111 CONNECT ACKnowledge Ack. Of connection

0000011 PROGRESS Establish. in progress

0000101 SETUP Request call establish.

0001101 SETUP ACK Request received



Group 2 Call Information Phase0100100 HOLD Holding a call

0101000 HOLD ACKnowledge Ack. Of Holding

0110000 HOLD REJect Reject Of Holding

0100110 RESUME Resume a call (TP service)

0101110 RESUME ACKnowledge ACK. Of resume (TP service)

0100010 RESUME REJect Reject Resume (TP service)

0110001 RETRIEVE Retrieve a call (HOLD service)

0110011 RETRIEVE ACKnowledge ACK. Of Retrieve (HOLD service)

0110111 RETRIEVE REJect Reject Retrieve (HOLD service)

0100101 SUSPEND Suspend a call (TP service)

0101101 SUSPEND ACKnowledge ACK. Of Suspend (TP service)

0100001 SUSPEND E REJect Reject Suspend (TP service)

0100000 USER INFOrmation User information



Group 3 Call Clearing Messages1000101 DISConnect Disconnect a call

1000110 RESTART Restart interface or channel

1001110 RESTART ACKnowledge ACK. Of restart

1001101 RELEASE Release a call

1011010 RELEASE COMPlete Call is released

Group 4 Miscellaneous Messages1111001 CONGESTION Control Flow control

1100010 FACility Facility message

1111011 INFOrmation Information messages

1101110 NOTIFY Call information (suspended, transfer …)

1100100 REGISTER Register of info

1100000 SEGMENT Segment of Message

1111101 STATUS Status of the Call State

1110101 STATUS ENQuiry Enquiry of Call State



SETUP

SETUP

SETUP ACK

ALERTINGALERTING

CONNECT

CONNECT

CONNECT ACK

CONNECT ACK

RELEASE

DISCONNECT

RELEASE

REL. COMPL

Calling TE

Called TEET ET

B CHANNEL ALLOCATED FOR COMMUNICATION

INFORMATION

CALL PROCEEDING

DISCONNECT

REL. COMPL

SS7 protocol

- TUP+ - ISUP







Bearer Capability,Channel Identification,Display,Keypad,Calling Party number,Calling Party Sub-address,Called Party number,Called Party Sub-address,Low Layer compatibility,High Layer compatibility,Facility,user-user information .....


ISDN Protocols / B-Channel Protocols

• Once “Connect Ack” is received, B channel is opened according specified Bearer. . (BC specified inside the SETUP message)

B channel

Voice / Telefony

Data 0101110011

or


ISDN Protocols / B-Channel Application

B channel

0101110011

Voice samplingand coding

A-Law (Europe)µ-Law (USA)

0101110011 CODEC


ISDN Protocols / B-Channel application

Router Mailserver

ISDN

TCP

IP

PPP

B channel

PPP

B channel

IP

Ethernet

TCP

IP

EthernetISDN ISDN

NT1

Router

S/T

LAN

FTP FTP


ISDN Protocols / B-Channel application

ISDN

ISDN ISDN

NT1

T.563, T.521, T.503

T.6

T.62

T.70

ISO 8208

X.75 LAPB

B channel

T.563, T.521, T.503

T.6

T.62

T.70

ISO 8208

X.75 LAPB

B channel

NT1FAX G4


Customer Premises Equipement

Network Termination/NT-AB Private Automatic Branch exchange Terminal Equipements


ISDN Supplementary Services

ISDN offers supplementary services as those which are available on PABX or on privatenetworks => gives a direct access to enhanced network function from a simple TE.

The following supplementary services are standardized by the ETSI organization:

Number Identification services

MSN Multiple Subscriber Number DDI Direct Dialling InSUB Sub-AdressingCLIP/CLIR Calling Line Identification Presentation/Restriction COLP/COLR Connected Line Identification Presentation/Restriction MCID Malicious Call Identification



Call Offering Services

TP Terminal Portability CFU Call Forwarding UnconditionalCFB Call Forwarding BusyCFNR Call Forwarding No Reply CD Call DeflectionMCID Malicious Call Identification

Call Completion Services

CW Call Waiting HOLD Call HoldCCBS Call Completion to Busy Subscriber



Multiparty

CONF Conference Call 3PTY Three-Party serviceECT Explicit Call Transfer

Community of interest

CUG Closed User Group

Charging services

AOC-S/D/E Advice of charge

UUS User to User signalling



Two Layers 3 activation modes for supplementary services:

1)- Stimulus signalling mode (keypad protocol and feature key management)

- keypad protocol uses the keypad information element in order to activate service in INFORMATION message

- Feature activation, deactivation and indication are conveyed in INFORMATION message in order to activate/deactivate services.

USER NETWORK

INFORMATION *32*2345#

INFORMATION Feature Activation 4



2)- General Functional protocol (Q.932 and ETSI specification)

- Based on the used of the FACILITY message and FACILITY information element- uses ASN.1 syntax- specific layer 3 messages for HOLD and TP services.

FACILITY IE[Serv.Invoke]

FACILITY IE[Serv.Return Result]

FACILITY IE[Serv.Return Reject]

FACILITY IE[Serv.Return Error]

USER NETWORK


Corporate/ Private Networks

PBX 1

PBX 2

PBX 3

FIXED LINKS

• Interconnection of several sites• Corporate networks in order for security and money savings

ISDN


Corporate/ Private Networks

PBX 1

PBX 2

PBX 3

• Standardization or inter-PABX protocol Q.SIG by the ECMA (European ComputerManufacturer Association).• Q.SIG protocols is the standard for inter PBX communication and has beenstandardized by ISO and ETSI organizations• Most of the manufacturers are now using Q.SIG as a platform for the developmentof inter-PBX functions (CorNet-NQ ....)• ISDN PBX Networking Specification: Alcatel, Ascom, ATT, Bosch, Ericsson, GPT,Italtel, ICC, Matra Communication, Nortel, Philips, Siemens AG.

Q.SIG

Documents

ISDN Basics