Lecture-3

Integrated Services Digital Network (ISDN) The ISDN

• The standards for ISDN was defined and 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. Integrated Digital Network (IDN)

• A combination of networks available for different purposes. • Access to these networks is by digital pipes • Digital pipes are 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. Principles of ISDN

1. Support of voice and non-voice applications using a limited set of standardized facilities – Defines the purpose of ISDN and the means of achieving it

2. Support for switched and non-switched applications – Both circuit-switched and packet-switched connections – Support non-switched services in the form of dedicated lines

3. Reliance on 64-kbps connections – Fundamental block of ISDN – 64 kbps were chosen because it was the standard rate for digitized voice

5 Principles of ISDN 4. Intelligence in the network – Sophisticated serviced beyond simple setup a circuit-switched call – Sophisticated network management and maintenance capabilities – Use of SS7 (signaling system 7) and intelligent switching nodes in the network – SS7 is a set of telephony signaling protocols which are used to set up the vast majority of the world's PSTN telephone calls. 5. Layered protocol architecture – User access to ISDN protocol is a layered architecture that can be mapped to OSI model – Standards can be developed independently for various layers and functions 6. Variety of configurations – More than one physical configuration is possible for implementing ISDN 6 The ISDN Network

7 The User Interface

•User has access to ISDN via a local interface to a digital “pipe” of certain . • Pipes of various sizes are available to satisfy different needs • Pipe to the user’s premises has a fixed capacity but the traffic on the pipe may be a variable mix up to the capacity limit. • ISDN requires control signals to instruct how to sort out the time-multiplexed data and provide the required services • Control signals are multiplexed onto the same digital pipe • At any time, the User may employ less than the maximum capacityof thepipe and will bechdharged according to the capacity used rather than “connect time”. Benefits • The principle benefits of ISDN to the customer can be expressed in terms of cost savings and flexibility • Carries a variety of user traffic, such as digital video, data, and telephone network services, using the normal phone circuit- switched network • Integrated voice and data means that the user does not have to buy multip leservices tomeet multip le needs. – Access charges to a single line only – Purchasing services based on actual needs – Product diversity, low price, and wide availability of equipment • Offers much faster call setup than modems by using out-of- band signaling (D channel) • Provides a faster data transfer rate than modems by using the 64-kbps bearer channel (B channel)

9 ISDN Architecture

NETE0510: Communication Media and Data 10 Communications ISDN Architecture

• The ISDN will su pport a completely new phy sical connector for users, a digital subscriber line and a variety of transmission services. • Physical interface provides a standardized means of attaching to the network that is usable for telephone, computer and videotext terminal. • The interface supports a basic service consisting of three time- multiplexed channels, two at 64 kbps and one at 16 kbps in addition with a ppyrimary service that provide multiple 64-kbps channels. • An interface is defined between the customer’s terminal equipment (TE) and a device on the customer’ s premises, known as a network termination (NT). • The subscriber loop is the physical path from the subscriber’s NT to the ISDN central office that must support full-duplex digital transmission for both basic and primary data rates ISDN Architecture

• The ISDN central office is connected to nmerosnumerous su bscriber lines to the digital network that provide various services: • Circuit Switched capabilities- operating at 64kbps and provide the same services like other digital switched network. • Non-switched capabilities- one such facility offers a 64kbps dedicated link; but at a higher rate provided by broadband ISDN. • Switched capabilities- high speed(>64kbps) switched connection provide ATM services as part of broadband ISDN. • Packet-switched capabilities- Provides packet switched services. • Frame mode capabilities- a service that support frame relay. • Common channel signaling capabilities- SS7 is used to control the network and provide call management. ISDN Channel Types

• ISDN uses bearer or B chlhannels for transmitti ng dtdata, and a signaling or D (delta) channel for transmitting signaling and control information. • There is also an H channel that is used for transmitting user data at higher transmission rates than the B channel. B chlhannel: • A 64-kbps clear channel used to transmit computer data (text and graphics), digitized voice, and digitized video. • B channel transmissions are either circuit- or packet switched. • Data also can be exchanged via frame relay or through a dedicated leased line arrangement. ISDN Channel Types

D chlhannel: • The D channel is either a 16-kbps or 64-kbps channel depending on the specific service level provided. • It is used to carry signal and control information for circuit switched user data. • The D channel transmits information related to call setup and termination between an ISDN device and the Telco's central office for each B channel. • The D channel also can be used to transmit packet-switched user data (provided that no signal or control information is needd)ded), dtdata from securityalarm silignalsof remote sensing devices that detect fire or intruders, and low speed information acquired from telemetry services, such as meter reading. ISDN Channel Types H channel: • The H chlhannel isused for tittitransmitting user data (not signal or control information) at Channel Data higher transmission rates than the B channel Rates provides. (Kbps) • Four H channels are defined: H0, H10, H11, and H12. Bearer (B) 64 • H0 comprises six B chlhannel, for a ttltotal capacity of 384 kbps. Data (D) 16, 64 • The H10 channel is US specific and aggregates 23 B channels for a total capacity of 1.472 Mbps. Hybrid (H) 384 (H0), 1472(H10), • The H11 channel is the equivalent of the North 1536(H11), American DS-1 and consists of 24 B channels 1920(H12) for an aggregate bandwidth of 1.536 Mbps. • The H12 channel, which is European specific, comprises 30 B channels and has an aggregate bandwidth of 1.920 Mbps. Types of Digital Subscriber Loops

• (BRI) • (PRI) Basic Rate Interface (BRI)

• The ISDN basic rate interface is a 192-kbps channel that consists of two 64-kbps B channels, one 16-kbps D channel, and 48 bits of overhead used for framing and other functions . • BRI provides a full duplex data rate of 128 kbps. • If call or signal information is not being carried by the D channel (e.g., transmitting data via packet-switching), then the rate increases to 144 kbps if the D channel is carrying data. • BRI is appropriate for the home or small office, Primary Rate Interface (PRI)

• The PRI has two standard configurations-the first is based on the North American DS1 (1.544-Mbps) format, and the second is based on the European E1 (2.048-Mbps) format. • PRI service is essentially the same as BRI except PRI has 23 (or 30) B channels instead of 2, and PRI's D channel operates at 64 kbps instead of 16 kbps. • In Europe, the PRI ildincludes 30 B chlhannelsand 2 D chlhannels to provide the capacity of 2.048 Mbps( E-1 line). • PRI is more appropriate for organizations that have to provide telecommunication services to a large number of sites.

Other channel combinations: – 3H0 + D – 4H0 + D – H12 + D ISDN Components

• Terminal Adapter (TA) - Converter device that converts standard electrical signals into the form used by ISDN - allows non-ISDN devices to operate on an ISDN network. • Terminal Equipment Type 1 (TE1) - Compatible with the ISDN network. Example: Telephones, personal computers, fax machine or videocon ferenc ing machine. • Terminal Equipment Type 2 (TE2) - Not compatible with the ISDN network. Example: Analog phone or modem, requires a TA (TE2 connects to TA). • NetworkTerminationType1&2(NT1andNT2)-Asmall connection box that physically connects the customer site to the Telco local loop, provides a four-wire connection to the customer site and a two-wire connection to the network. ISDN Components Network Termination Type1(NT1)- • Controls the physical & electrical termination of the ISDN at the user’s premises. • CtConnects theuser’s itinterna lsystem to the digit a l subibbscriber 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. Network Termination Type 2 (NT2)- • Performs functions at the physical (multiplexing), data link (flow contl)trol),netktwork layers (ktii)(packetizing) of the OSI modldel • Provides intermediate signal processing between the data- gggenerating devices and an NT1 • Used primarily to interface between a multiuser system and an NT1 in a PRI. ISDN Components and Reference Points ISDN Reference Points

• U-Describes full-duplex data signal on the subscriber line. -Two wire cable that connects the customer’s equipment to the provider • R-Point between non-ISDN equipment (TE2) and the TA. - not defined by ISDN, can be any EIA standards or V or X series. • S-ISO standard, -fiihtfour, six or eight-witiire connection cable from TE1 or TA t o th eNT 2. • T-Point between NT1 and NT2 Home‐based ISDN Internet

Figure: A typical home‐based ISDN Internet connection consists of a BRI connection from the home to the telco’s ISDN network and a PRI connection between the ISP and the telco’s ISDN network. The entire connection, from home to ISP, is completely digital. Home‐based ISDN Internet connections are an alternative to conventional analog dialup connections using 28.8‐kbps or 56‐kbps modems. ISDN Protocol Layers

• ISDN essentially is unconcerned with user layers 4-7. These are end to end layers employed by the user for exchange of information. • Network access is concerned only with layers 1-3.

Physical layer ISDN protocols: • Layer 1 defines the physical interface for BRI and PRI. • BRI is defined by the ITU-T I.430 protocol and PRI is defined by ITU-T I.431, which describes the physical connections between the ISDN Customer Premises Equipment (CPE) and the ISDN local exchange. • I.430 also defines two ISDN physical layer frame formats. • The B and D channels are multiplexed over the same physical interface and above this layer the protocol structure differs for the two channels. ISDN Protocol Layers Data link layer ISDN protocols: • For the data link layer a new standard LAPD (link access protocol for D channel) and LAPB (link access protocol for B channel) is defined. • LAPD siliignaling protltocol (ITU-T Q.920 for BRI and Q.921 for PRI) for transmitting control and signaling information over the D channel • All transmission on the D channel is in the form of LAPD frames exchanged between the subscriber equipment and ISDN switching element. Network layer ISDN protocols: • ITU-T I.930 and ITU-T Q.931 defines switching and signaling methods using the D channel. •For control signaling a call control protocol Q.931 has been defined to establish, maintain and terminate connections on B channels. •X.25protocol is used to establish virtual circuits on the D channel to provide packet switching services. ISDN Protocol Layers

Mechanical and electrical specs of interfaces R, S, T, U

Encoding

Multiplexing

Power supply BRI Frame • Each ISDN BRI frame contains two sub-frames each containing the following: – 8 bits from the B1 channel, 8 bits from the B2 channel, 2 bits from the D channel, and 6 bits of overhead

• So, each BRI frame contains 48 bits A‐ Activation bit B1‐B1 channel bits B2‐ B2 channel bits D‐ D channel bits E‐ Echo of previous D bit F‐ Framing bit L‐ Loading balance bit S‐ Spare bit

overhead ISDN Physical Layer

• 4,000 frames are transmitted per second. • Each B channel, B1and B2, has a capacity of 8 * 4000 * 2 = 64 kbps, while channel D has a capacity of 2 * 4000 * 2 = 16 kbps. • This accounts for 144 kbps (B1 + B2 + D) of the total ISDN BRI physical interface bit rate of 192 kbps. • The remainder of the data rate are the overhead bits that are required for transmission: 6 * 4000 * 2 = 48 kbps.

28 PRI Frame ISDN Data-link Layer •Layer 2of the ISDN sigggnaling channel is LAPD. • LAPD is used across the D channel to ensure that control and signaling information is received and flows properly. • The frame format for the Link Access Protocol for D channel is shown in Figure

30 ISDN Data-link Layer •Flag - Signals the beggginning or ending of the frame. •Address-Provides addressing information. The service access point identifier (SAPI) identifies where the layer-2 protocol provides service to layer 3. Specific addresses identify specific services. For example SAPI = 16 is for X.25 packet data transmissions. • The command/response (C/R) bit specifies whether - the frame is a command or response. • The extended address (EA) bits specify the beginning and ending of the address field. If EA is 0, then another byte of address information follows. An EA of I implies that the current byte is the last byte of the address. Thus, given a two-byte address, EA = 0 in the higher-order byte and EA = I in the lower-order byte. • The terminal endpoint identifier (TEl) represents the specific address or ID assigned to each ISDN terminal equipment connected to an ISDN network via an S/T;Interface. • Control - Provides layer-2 control information (e.g., specifies the type of frame being transmitted, maintains frame sequence numbers). • Information- Provides layer-3 protocol information and user data. Addressing in ISDN •AnISDN address Com pri ses ttehe ISDN nuubember aadnd aayny man dator y and/or optional addressing information. • An ISDN number is associated with a D channel which provides common channel signaling for a number of subscribers with ISDN

address National ISDN Number

International ISDN Number

• Country Code - Composed of a variable number of decimal digits (1 to 3) specifies the destination country of the call. • National Destination Code (NC) – Variable length number used to route the call over the destination network to a particular region of the network. • ISDN Subscriber Number- Variable length number to be dialed to reach a subscriber in the same local network or numbering area. • ISDN Sub address – Max 40 digit number identify the device connected to NT1 ISDN Services Bearer services – • Provide the means to transfer information (voice, data, video) between users in real time without manipulating the content of that information. • Belongs to the first 3 layers of the OSI model. Teleservices – • Combines the transportation function with the information processing function. • Employ bearer services to transport data. • Provide a set of higher layer functions correspond to layers 4-7 of the OSI model. Supplementary services – • UdUsed inconjtijunction with one or more of the bearer or teleservices. • Provide additional functionality to the bearer services and teleservices. • Can not be used alone. ISDN Services

Videotext Video teleppyhony