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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.
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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.
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ISDN Services
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Voice Communication over an Analog Telephone Network
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Voice and Data Communication over an Analog Telephone Network
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Analog and Digital Services over the Telephone Network
3 types of customers – the first one is the most prominent
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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.
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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.
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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
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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
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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
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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 Mbps – the capacity of E-1 line
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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.
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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.
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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)
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Reference Points Label used to identify individual interfaces between two elements of an ISDN installation Defines the functions of the connections
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ISDN Layers
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OSI Model
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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
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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
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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
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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
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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
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The OSI Model Physical Layer Message Has Begin and End Data in between
Data Passed up to Link Layer Begin End Data Link Layer
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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
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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
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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
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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
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The OSI Model Complete Picture A Message with All Headers
Session, Presentation, Application Omitted Trans Hdr Data Net Hdr LL Hdr Begin End
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Simplified Layers of ISDN
Mechanical and electrical specs of interfaces R, S, T, U Encoding Multiplexing Power supply
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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
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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
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2B/1Q Encoding 00 01 10 11 -3 -1 +3 +1
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BRI Frame overhead
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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
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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
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PRI Frame
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LAPD Address Field SAPI – Service Access Point Identifier
– call control for network layer (signaling use of D-channel) – call control for upper layer (ene-to-end signaling), not yet in use – packet communication ( data use of D channel) 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
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Network Layer Packet Format
Protocol discriminator – identifies the protocol in use, for Q.931 = 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
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Call Reference Field
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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)
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Information Element Types
ID – identify the information being sent Length – length of the content in bytes
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Addressing in ISDN Addressing – important information element type in ISDN NC – national Code Subaddress – identify the device connected to NT1
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Bit Rates for Different Applications
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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
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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
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B-ISDN Accesses Mbps – fill the needs of most residential and many business subscribers / Mbps – fill the needs of businesses that require the simultaneous receipt of multiple services and video conferencing
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