Integrated Services Digital Network (ISDN) Developed by ITU-T in 1976 Set of protocols that combines digital telephony and data transport services. The whole idea is to digitize the telephone network to permit the transmission of audio, video and text over existing telephone lines. The goal is to form a WAN that provides universal end-to-end connectivity over digital media.

ISDN Services Bearer services – provide the means to transfer information (voice, data, video) between users without the network manipulating the content of that information. Belongs to the first 3 layers of the OSI model. Teleservices – the network my change or process the contents of the data. - correspond to layers 4-7 of the OSI model - rely on the facilities of bearer services Supplementary services – provide additional functionality to the bearer services and teleservices.

ISDN Services

Voice Communication over an Analog Telephone Network

Voice and Data Communication over an Analog Telephone Network

Analog and Digital Services over the Telephone Network 3 types of customers – the first one is the most prominent

Integrated Digital Network (IDN) A combination of networks available for different purposes. Access to these networks is by digital pipes digital pipes – time-multiplexed channels sharing very-high-speed paths.

Integrated Services Digital Network (ISDN) ISDN incorporates all communication connections in a home or building into a single interface With ISDN all customer services will become digital rather than analog.

Subscriber Access to the ISDN Subscriber loops – organized into multiple channels of different sizes B channel basic user channel Can carry any type of digital info in Full-duplex mode Carries transmissions end-to-end D channel Primary function is to carry control signaling for the B channel Acts like an operator between the user and the network at the network layer Channel Data Rates (Kbps) Bearer (B) 64 Data (D) 16, 64 Hybrid (H) 384 (H0), 1536(H11), 1920(H12) H Channels - For high data rate applications such as video, teleconferencing and so on

Two Types of Digital Subscriber Loops Basic rate interface (BRI) Primary rate interface (PRI) Each type is suited to a different level of customer needs Both include one D channel and some number of either B or H channels

Basic Rate Interface (BRI) Designed to meet the needs of residential and small-office customers The same twisted pair local loop that delivers analog transmission can be used to handle digital transmission

Primary Rate Interface (PRI) Other channel combinations: – 3H0 + D – 4H0 + D – H12 + D PRI was designed to be compatible with existing T-1 lines In Europe, the PRI includes 30 B channels and 2 D channels = capacity of 2.048 Mbps – the capacity of E-1 line

Functional Grouping Defines the function of each type of equipment NT – network termination TE – terminal equipment NT1 Controls the physical & electrical termination of the ISDN at the user’s premises Connects the user’s internal system to the digital subscriber loop Organizes the data stream s from a connected subscriber into frames that can be sent over the digital pipe Translates the frames received from the network into a format usable by the subscriber’s devices.

NT2 ( ex. Digital PBX, LAN) Performs functions at the physical (multiplexing), data link (flow control), network layers (packetizing) of the OSI model Provides intermediate signal processing between the data-generating devices and an NT1 Used primarily to interface between a multiuser system and an NT1 in a PRI.

TE1 – same thing as DTE TE2 Any non-ISDN device Any device that supports the ISDN standards Ex. Digital telephones,integrated voice/data terminals TE2 Any non-ISDN device Ex. Terminal workstation, regular telephone Can be used with the help of Terminal Adapter (TA)

Reference Points Label used to identify individual interfaces between two elements of an ISDN installation Defines the functions of the connections

ISDN Layers

OSI Model

The OSI Model Open Systems Interconnection Standard Model for Data Communications Specified by International Standards Organization (ISO) Adopted by CCITT/ITU Official Model Explained in X.200 Series

The OSI Model Layered Approach to Communications Seven Layers Altogether Each Layer Performs a Unique Function Each Layer Has Its Own Protocol Protocol Messages in Upper Layer is Data to Layer Below

7 Layers All People Seem To Need Data Processing 7. Application Layer Presentation Layer Session Layer Transport Layer Network Layer Data Link Layer Physical Layer All People Seem To Need Data Processing

The OSI Model The Seven Layers Layer Name Description Examples Physical Link Network Transport Session Presentation Application Unreliable Wire, Telco Line Reliable Across Physical Line Unreliable Thru Multi-Node Network Reliable End to End Sync Points and Dialogs Data Representation & Syntax User Level Processing RS232, T1, 802.x LAPB, HDLC X.25 Pkt, IP TCP ISO Session ISO Presentation Telnet, FTP, Mail

The OSI Model The Standards Layer Name Standards Physical Link Network Transport Session Presentation Application X.400, Telnet, FTP, Mail ASN.1, X.409 X.225 X.224, TCP X.25 Pkt, Q.931, IP Reliable Across Physical Line X.25 LAPB, Q.921 LAPD, ISO 3309 HDLC RS232, V.35, EIA530, X.21, T1, E1 Unreliable Wire, Telco Line Unreliable Wire, Telco Line

The OSI Model Physical Layer Message Has Begin and End Data in between Data Passed up to Link Layer Begin End Data Link Layer

The OSI Model Physical Layer Begin Can Be Flag or STX End Can Be Flag or ETX End May Include Check Sum (CRC) Data Transparency Link Layer Begin Data End

The OSI Model Link Layer Link Layer Header Has Frame Type Sequence and Acknowledgement Numbers Error Recovery Procedures Limited to Local Wire or Circuit Network Layer LL Hdr Data

The OSI Model Network Layer Network Header Has Packet Type Sequence and Acknowledgement Numbers No Error Recovery -- Data Can Be Lost Addressing across Multi-Node Network Transport Layer Net Hdr Data

The OSI Model Transport Layer Transport Header Has Packet Type Sequence and Acknowledgement Numbers Error Recovery Is End to End Upper Layers Can Count on Reliability Upper Layers Trans Hdr Data

The OSI Model Complete Picture A Message with All Headers Session, Presentation, Application Omitted Trans Hdr Data Net Hdr LL Hdr Begin End

Simplified Layers of ISDN Mechanical and electrical specs of interfaces R, S, T, U Encoding Multiplexing Power supply

BRI Interfaces R interface – not defined by ISDN, it can be any EIA standards or V or X series S interface – ISO standard, ISO 8887, four-, six-, or eight-wire connections. U interface - Single-pair twisted-pair cable in each direction - Two binary, one quaternary (2B1Q) encoding

S Interface Name TE NT a Power source 3 Power sink 3 b c Transmit Receive d e f g Power sink 2 Power source 2 h

2B/1Q Encoding 00 01 10 11 -3 -1 +3 +1

BRI Frame overhead

BRI Topology Point-to-point Multipoint -limited distance to ensure frame synchronization As many as 8 devices can be connected to NT1, two can access the B-channels at 1 time D channels use a mechanism like CSMA

PRI Interfaces R and S – same as those defined for the BRI T – identical to S standard - B8ZS Encoding U – same for both, different rates

PRI Frame

LAPD Address Field SAPI – Service Access Point Identifier 000000 – call control for network layer (signaling use of D-channel) 000001 – call control for upper layer (ene-to-end signaling), not yet in use 010000 – packet communication ( data use of D channel) 111111 - management SAPI – Service Access Point Identifier - identifies the type of upper- layer service (network layer) C/R – Command (0) / Response (1) TEI – Terminal Equipment Identifier

Network Layer Packet Format Protocol discriminator – identifies the protocol in use, for Q.931 = 0000 1000 Call Reference – sequence number of the call Message Type – identifies the purpose of the message - call establishment - call information - call clearing - call miscellaneous Reading assignment: Different messages under these four message types

Call Reference Field

Information Elements Carries specific details about the connection that are required for call establishment: - addresses of the sender and receiver - routing information - type of network that is desired for the B-channel exchange (X.25, ATM, Frame Relay)

Information Element Types ID – identify the information being sent Length – length of the content in bytes

Addressing in ISDN Addressing – important information element type in ISDN NC – national Code Subaddress – identify the device connected to NT1

Bit Rates for Different Applications

B-ISDN Services Broadband ISDN – based on a change from metal cable to fiber optic cable at all levels of telecommunications Interactive services – those that require two-way exchanges between either 2 subscribers or between a subscriber & a service provider - conversational – real time exchanges such as telephone calls - messaging – store & forward exchanges such as voice mail - retrieval –retrieve info from a central office

B-ISDN Services Distributive services – unidirectional services sent from a provider to subscribers, broadcast to the user - without user control – user choice is limited to whether or not to receive the service at all - with user control – allow the user a choice of times during which to receive them

B-ISDN Accesses 155.520 Mbps – fill the needs of most residential and many business subscribers 155.520/622.080 Mbps – fill the needs of businesses that require the simultaneous receipt of multiple services and video conferencing

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