Network Technologies (I) Data Transmission Transmission Media Cabling Systems LAN Technologies Ethernet Token Ring FDDI

Data Transmission Message Source XMTR Modulator Channel RCVR Noise Interference Distortion

Data Transmission Transmission of data depends on Quality of signal Characteristics of medium Need to do signal processing Need to measure quality of received signal Analog: signal-to-noise ratio Digital: probability of symbol error To transmit bits (0’s or 1’s) we need to map them into electromagnetic waves. Modulation techniques.

Data Transmission Transmitted signals are Attenuated Distorted Corrupted by noise Attenuation and distortion depend on Type of transmission medium Bit rate Distance Medium determines Data rate Bandwidth of channel

Data Transmission Medium: Direct link: point-to-point or guided Guided: twisted pair, coaxial cable, optical fiber Unguided: radio, satellite, infrared, microwave Direct link: point-to-point or guided Two devices share the medium (intermediate repeaters, amplifiers) Indirect link: multipoint or broadcast More than two devices share the medium Transmission modes: simplex, half-duplex, full-duplex Frequency, spectrum, bandwidth Time-domain vs. frequency domain

Data Transmission Bandwidth: several criteria, choice depends on application (3dB or 50% power; fraction of signal power) Nyquist formula Maximum data rate as a function of channel bandwidth (BW) if BW=B then max. data rate is 2B 2 levels per signaling element General C = 2B log2 (M) [bps], M = levels per signaling element

Data Transmission Attenuation: strength of signal falls off with distance; increases as a function of frequency Delay distortion: propagation velocity varies with frequency; different frequency components arrive at different times Noise: thermal, intermodulation, crosstalk, quantization, impulse Data rate: C = B log2 (1 + S/N) [bps]

Transmission Medium Twisted pair Coaxial cable Optical fiber Wireless

Transmission Medium Twisted pair (UTP, STP) two insulated copper wires arranged in a spiral fashion wire pair acts as a single communication link twist length varies from 2-6 inches thickness varies from 0.016 to 0.036 inches used in telephone networks used within buildings inexpensive compared to other media easy to work with poor noise and interference immunity twisted to avoid crosstalk

Transmission Medium Twisted pair (UTP, STP) analog signal amplifiers required every 5 to 6 km digital signal repeaters required every 2 to 3 km interference reduced by sheating UTP: ordinary telephone wire, cheapest media for LANs, subject to interference STP: less prone to interference, more expensive, harder to work with EIA-568-A standard recognizes category 3 UTP capable of 16MHz category 4 UTP capable of 20 MHz category 5 UTP capable of 100MHz

Data Rate Capacity of UTP Cables Capacity Mb/s 1000 NEXT - Dominated Environment 800 Category 5 600 Category 4 400 Category 3 200 100m Horizontal Link (ft) 100 200 300 400 500 600 700 800

Transmission Medium Coaxial cable hollow outer cylindrical conductor surrounding a single inner wire regularly spaced insulating dielectric hold inner conductor in place jacket or shield covers the outer conductor diameter 0.4 to 1 inch television distribution: CATV long distance telephone transmission short run computer I/O channels LANs better frequency characteristics, higher data rates, and more immune to interference than twisted pair

Transmission Medium Optical fiber 2 to 124 um flexible medium conducts and optical ray core: innermost section; cladding: middle section forms a plastic coating over the core; jacket: the outer most section covering the cladding data rates of 2Gbps over tens of km significantly low attenuation not susceptible to interference or crosstalk used for: long haul, metropolitan, and rural trunks, subscriber loops and LANs

Transmission Medium Optical fiber Multimode transmission rays entering the core reflect and propagate along the fiber Single mode transmission radius of core reduced to one wavelength only a single angle of reflection is allowed provides superior transmission XMTR: light-emitting diode (LED) or injection laser diode (ILD) RCVR: photodiode or photo transistor

Transmission Medium Wireless terrestrial microwave satellite microwave broadcast radio infrared laser

Transmission Medium Terrestrial microwave requires line of sight requires fewer amplifiers or repeaters long haul telecommunication services voice and TV transmission point-to-point links between buildings

Transmission Medium Satellite microwave relays used to link ground stations functions as an amplifier or a repeater can provide point-to-point to point-to-multipoint connectivity television distribution long distance telephone transmission private business networks

Transmission Medium Broadcast radio omnidirectional does not require complex antennas antennas need not be precisely aligned FM radio VHF and UHF television data networks

Transmission Medium Infrared XMTR/RCVR (transceivers) modulate non-coherent infrared light line of sight is needed no frequency allocation is needed provides point-to-point connectivity

Cabling Systems Evolution 1980’s View, Dedicated Application Proprietary Wiring, Central Processing, Voice and Data Separate 1990’s View, Integrated Open Architecture Wiring System, Voice/Data/Image/Video Need for High-Speed Transmission, 100/155 Mbps and Higher, Require Significantly more Bandwidth

Cable Systems Evolution 1G Data Rate bps 622 Mb/s 100M TP-PMD ATM 10BASE-T 16M Token Ring 10M 4M Token Ring Baseband Video IBM 3270 1M StarLAN 1 100K DCP 10K EIA-232 1K 1975 1980 1985 1990 1995 2000 Year

Cabling Systems Evolution Cable systems must be developed to address: Non Compatible Non Standard Conventional Type Wiring Plans Designed to ease the introduction of new computer systems, LANs and PBXs

Cabling Systems Concerns Installing and Maintaining a Reliable Cable Plant is Essential to the Well-Being of Today’s Mission Critical LANs Category 5 UTP is Today’s Preferred Choice for LAN Cabling Why is Category 5 UTP the Best Bet for Horizontal Wiring? How Does it Handle 100/155 Mbps + Data Rates? How Do You Maximize the Performance of Your UTP Installation?

Cabling Systems Concerns Voice: Wiring system placed by PBX vendor or telephony networks to all identified work locations Data: Wiring placed by data networks on an as needed basis Proprietary Application Media (Coax, Dual Coax, Shielded) Data Processing Systems - Mainframe (IBM 3270, IBM System 36/38 AS 400, etc..) PC - Stand alone

Cabling Systems Concerns LAN electronics vendors estimate cabling problems account for 50% of all LAN failures and problems LAN Technology stated that 70% of downtime is attributed to cable related problems A Communications Week study in January 1992 Found network downtime cost small companies $3,200.00 per hour Infonectics Corporation study in October 1993 found network downtime cost Fortune 1000 companies an average of $62,500 per hour.

Network Costs 34% 5% 7% LAN Wiring Intelligent Workstation Wiring LAN Attachment 5% LAN Attachment 7% Software & Mainframe Intelligent Workstation 54% Software & Mainframe

Cabling Systems Trends 100 Mbps over Copper, solutions for UTP already exist 100 Mbps over Fiber, Momentum has Slowed Fast Ethernet* 100 Mbps, on both CAT3 and CAT5 Cables ATM 155 Mbps do-able Theoretical limits of some manufactures CAT5 cables is more than 950 Mbps at 100 Meters.

Cabling Systems Properties Open Architecture Integrated Distribution Plan Standards Compliant Cost Effective End-to-End Offering Full Functionality and Flexibility Manageable Growth Investment Protection

Network cabling Networking supports transmission and reception of data. Network cabling provides the physical path for transmission and reception of data. 1

Overview Transmission media typically used Bounded media Electrical conductors (eg coaxial cable, twisted wire pairs). Optical conductors (eg Optical Fiber ). Waveguides (air is the transmission medium but the waveguide confines or “binds” the transmission). Unbounded media Transmission of electromagnetic waves or light through air or space.

Bounded media Also known as guided media. Bounded transmission media constrain and guide communication signals. Media using electrical signals are Single conductor Paired cable and Coaxial cable

Bounded media ( Cont.) Media using light signals Optical fiber Media using electromagnetic waves Waveguides

Single conductor A single conductor is used to provide a path for an electric current. The earth provides the return path ( since a circuit needs to be complete for current to flow). Today, used for short distances, like on a circuit board or on a silicon chip.

Paired cable Two Conductors are used, with second conductor providing the return path for the signal current. Two cables can be Open wire pair (parallel to each other ). Unshielded twisted pair ( twisted ). Shielded twisted pair (seldom used today). Open wires are susceptible to to cross talk and electromagnetic interference and are seldom used.

Paired cable (Cont.) To avoid cross talk and interference the pairs of conductors are twisted. A twisted pair consists of 2 insulated copper wires twisted together. Usually number of these pairs are bundled together into a cable. Long distance cables may contain hundreds of pairs (eg telephone cables).

Paired cable (Cont.) Twisting decreases the cross talk interference between adjacent cables by confining the electromagnetic field. Twisted pair can be used for short distances ( usually less than 10 miles). Longer distances require repeaters to regenerate the signal.

Paired cable (Cont.) It has bandwidth limitations, when used over long distances. It is susceptible to noise since not all interference is eliminated. It is widely used for local telephone and data transmission.

Paired cable (Cont.) It provides the “local loop” for telephone but the bandwidth is limited. It can support 155Mbps transmission over short (less than 30ft) distances. It is therefore widely used for network cabling within buildings (intrabuilding cabling).

Coaxial cable Coaxial cable consists of two conductors. An inner conductor is completely sorrounded by an outer conductor. The two conductors are separated by high quality insulation. The outer conductor is sorrounded by a protective sheath.

Coaxial cable (Cont.) Coaxial cables can be used for transmission of high frequency signals. Using frequency or time division multiplexing (FDM or TDM) many channels can be supported by single cable. It is widely used for cable TV.

Coaxial cable (Cont.) It was widely used for (thick and thin cable) ethernets but it is being rapidly displaced by unshielded twisted pairs for this purpose.

Waveguides A waveguide is a rectangular or circular pipe, usually made of some conductor such as copper. It confines and guides very high frequency radio waves between two locations. Waveguides are used for signals in the range of gigahertz (GHz) frequencies where twisted pair or even coaxial cables are not effective.

Optical fibers Optical fiber is a thin, flexible glass or plastic fiber through which light energy is transmitted. An optical fiber is actually a waveguide that guides the propogation of optical frequency waves through total internal reflection.

Optical fibers (Cont.) Since most of the data that need to be transmitted are in the form of electrical signals, these signals must be converted to light signals before they can be transmitted by optical fibers.

Optical fiber communication system Transmitter Optical Fiber Optical Receiver Information Information Multiplexer Optical Receiver Optical Repeater Optical Transmitter Multiplexer FIG. 1. Typical optical fiber communication system.

Optical fibers (Cont.) Fiber optic transmission systems have transmitters which use LED (Light emitting diode) used primarily for short distances (< 2km) transmission or LASER diodes used primarily for longer distance transmission to convert electrical signals to light signals.

Optical fibers (Cont.) The receiver uses a photo diode to convert the light signals back to electrical signals. It offers large bandwidth. Signal loss is very low. Fibers are immune to electromagnetic interference.

Optical fibers (Cont.) A basic optical fiber consists of two concentric layers, the inner core and the outer cladding which has a specific refractive index lower than the core. There are 2 types of refractive index profiles, step and graded For a step profile fiber, the inner core’s refractive index is uniform, for a graded fiber, the profile inner core’s refractive index is not uniform.

Characteristics of optical fiber

Optical fibers (Cont.) There are 3 basic types of fibers In multimode Single mode. Multimode graded index. In multimode Inner core diameter is relatively large (50 to 62.5 microns). Light travels in different modes.

Optical fibers (Cont.) In single mode fibers Used for short or medium distances ( < 2km). Cheap compared to other types. Supports medium to high bandwidths. In single mode fibers Inner diameter is very small, typically 0.8 to 1 micron. Light travels in single mode. Used for medium and long distances (> 2km). More costly than multimode fiber. Can support very high bandwidths (6 Gbps).

Optical fibers (Cont.) In multimode graded index fibers Core is relatively large but difficult to manufacture. Properties are intermediate between single and multimode fibers. Because of difficulty in manufacture, such fibers are seldom used in data networking.

Unbounded media No physical connection is required. Space or air is the transmission medium for electromagnetic waves. Source and destination can be static or mobile. Broad spectrum from low to high bandwidth is available. Can be quickly implemented.

Unbounded media (Cont.) It is prone to interference. Transmission spectrum has to be shared and must be controlled to prevent interference in any given location. Different unbounded communication systems Broadcast radio and television. Terrestrial microwave. Satellite. Infra red.

Network cabling Transmission media of interest for network cabling Twisted pair Coaxial Fiber Wireless

Twisted pair Least expensive. Flexible Easy to install Widely used. There are two varieties UTP ( Unshielded twisted pair ). STP ( Shielded twisted pair ).

UTP Least expensive and popular. It is light and flexible. Easy to install. It is not shielded by external conductors. It is subject to electromagnetic interference and external noise. Twisting minimizes electromagnetic interference.

UTP (Cont.) For data transmission 3 categories of UTP cabling can be used Category 3 (cat 3 is for data rates upto 16 Mbps) Category 4 (cat 4 is for data rates upto 20 Mbps) Category 5 (cat 5 is for data rates upto 100 Mbps and even 155Mbps for limited distances)

UTP (Cont.) Cat 3 and Cat5 are used extensively Cat3 is voice grade cable and widely used for telephone. It has 3 to 4 twists per foot. Cat 5 is data grade cable and widely used for data networking.

UTP (Cont.) It has 6 to 12 twists per inch. Tighter twisting provides better performance but is more expensive. Characteristic impedance of both cat 3 and cat 5 is 100 Ohms. Cat5 is recommended, for data since it can support higher bandwidths.

STP Twisted pairs of copper wire are sorrounded with metallic braid or sheathing. Interference is reduced due to sheathing. Characteristic impedance is 150 Ohms. At lower data rates STP provides better performance than UTP. It creates less electrical noise. It is more expensive.

STP (Cont.) It is bulky. Less flexible. Installation is more expensive. Difficult to work with compared to UTP.

Coaxial cable It consists of single copper conductor at its center surrounded by a hollow cylindrical outer conductor, with the 2 conductors separated by a dielectric medium. Outer conductor provides a shield. Coaxial cable is highly resistant to signal interference because the electromagnetic field is confined between the inner and outer conductors.

Coaxial cable (Cont.) Less susceptible to cross talk than twisted pair cable. It can support greater cable lengths between network devices than twisted pair cables. It can support much larger bandwidths than twisted cable pairs. It is bulky.

Coaxial cable (Cont.) More difficult to install and work with than twisted pair cables. It is more expensive than twisted pairs. Coaxial cable was used in thin ethernet (10Base-2) and thick ethernet (10Base-5), but is now largely being replaced by cat5 UTP.

Fiber optic cable An optical fiber is a thin (0.8 to 125 µm), flexible medium capable of conducting light. It has the ability to transmit signals over much longer distances than coaxial and twisted pair cables. Very high data rates (gigabits per second ) can be achieved over optical fiber.

Fiber optic cable (Cont.) Theoretically 50Gbps are possible over fiber optic. Data rates of 4.8 Gbps over tens of kilometers have been demonstrated. Current dat rates are limited by the electronics and the optical transmitter/receivers. Optical fiber has the advantage of being thinner and lighter over coax or a bundle of twisted pair cables.

Fiber optic cable (Cont.) It has lower attenuation than coax and twisted pair cables. Since it transmits light, the problem of electrical interference is eliminated. It is also immune to the environmental (eg. moisture, lightening) disturbances.

Fiber optic cable (Cont.) The advantage of optical fiber over coax and twisted pair will be more compelling as the demand for greater bandwidth increases. It is highly secure medium, because it is difficult for any break to go undetected. The main disadvantage is it is very expensive Installation is expensive.

Fiber optic cable (Cont.) Cannot tolerate small bending radius. Difficult to work with because it is delicate.

Wireless Wireless media has the benefit of relatively inexpensive installation in an environment where users are mobile. It can also be beneficial in extending the network without rewiring the existing network. The 3 ways in use as of now are Microwave Spread spectrum Infrared

Microwave signals Uses a highly directional antenna to minimize interference. Frequencies used for transfer of information are dedicated. Usually suports point to point transmission. FCC regulates the bandwidth allocation.

Microwave signals (Cont.) Has the disadvantage of using only part of the total available bandwidth. Microwave signals can cross through walls and physical barriers. Prone to interference from other sources of microwave signals.

Microwave signals (Cont.) In general, it is relatively expensive but it may be the cheapest form of transmission over rough and mountainous terrain. Requires high power. Data rates upto 500 Mbps are possible. Exposure to microwave radiation may be risky (health wise).

Spread spectrum It doesn’t require FCC license. In this method each node has a radio transceiver. Each node uses an antenna to send and receive information. The signal to be transmitted is spread over a broad range of frequencies, so that signals look like noise.

Spread spectrum (Cont.) The receiving station extracts its message, thus allowing a greater number of users to share the bandwidth. There are 2 ways to do this Frequency hopping. Direct Sequence.

Spread spectrum (Cont.) In frequency hoping the transmission frequency is made to hop (change) rapidly. The receiver also hops in synchronism with transmitter and picks up the message. In direct sequence method, each bit is chipped into multiple bits using a bit pattern (thus spreading the signal over wider frequencies), with the help of same bit pattern receiver detects the bits. Data rates of upto 1-2Mbps are achievable.

Infrared In this method infrared light is modulated by transmitter. Transceivers must be in line of sight either directly or via reflection from a light colored surface such as a ceiling of a room. Data rates of upto 20Mbps are possible. No security or interference problems, as infrared transmission does not penetrate the walls.

Infrared (Cont.) License is not required. Short range, point to point and potential eye damage if exposed to IR rays are the main disadvantages of infrared transmission.

Standards based cabling Unstructured cabling No single standard is followed for interconnection Low initial cost, more expenses later. Difficulties in the long run with developing technologies. Difficulty in maintenance and scalability Structured cabling increases initial cost but can avoid the problems and future expenses.

Standards based cabling (Cont.) Telecommunications industry and the users realized the need for cost effective, efficient cabling systems.

Standards based cabling (Cont.) Electronic Industries Association (EIA), Telecommunications Industry Association (TIA) and other leading telecommunication companies worked cooperatively to create ANSI/TIA/EIA-568-A standard for commercial buildings. This standard defines structured cabling, a telecommunication cabling system that can support virtually any voice, imaging or data applications that an end user chooses.

TIA/EIA 568-A standard EIA/TIA 568-A specifications address Recognized media. Topology. Cabling distances. User interfaces. Cabling and Connecting hardware performance. Installation practices. Link performances.

Cabling elements Horizontal Cabling. Backbone Cabling. Work Area (WA). Telecommunications closet (TC). Equipment Room (ER). Entrance Facility (EF).

Horizontal cabling It extends from the telecommunications outlet in the work area to the horizontal cross connect in the telecommunications closet. Terminal Work Area Telecommunications Closet

Horizontal cabling (Cont.) It includes The outlet. Horizontal cables. Mechanical terminations and Patch cords (or jumpers) that comprise the horizontal cross connect (each outlet in work area is connected to a horizontal cross connect in the telecommunications closet) .

Horizontal cabling (Cont.) Specifications here are about Proximity to EMI. No. of outlets for each individual workarea. UTP, STP and Fiber are recognized. Coax is recognized but not recommended for new cabling installations. Horizontal cabling shall be configured in star topology. Other such issues.

Backbone cabling The backbone cabling system provides interconnections between Telecommunication closets. Equipment rooms. Entrance facilities. It also includes the vertical wiring between floors, hence also known as vertical wiring. Backbone also extends between buildings in a campus environment.

Backbone cabling (Cont.) The specifications include Backbone cables. Intermediate and main cross connects including mechanical terminations. Patch cords or jumpers used for backbone to backbone cross connections. Recognized cables here are UTP, STP, Multimode and single mode fiber.

Work area Work area specifications consist of Cable connecting user station to wall plate. Devices connecting the user station to the wall plate. Work area wiring is typically UTP or STP.

Telecommunication closet Also known as wiring closet. One on each floor (typically, depending on the floor space and special requirements number may vary). Standards complaint connecting hardware should be used. Specifications about short cables (patch chords) are made.

Equipment room In large office buildings, there will be centralized equipment rooms to house servers, hubs, modems etc. It is the central interconnection point for network cabling. Main cross connections are specified here.

Entrance facility It is the network entry point of the building. Within the network entrance facility, a cross connect device provides a termination point for all the cables. Interfaces are specified. Interconnection for cross connect devices and network devices are specified.

Other specifications In addition to the cabling elements in TIA-568-A, there are specifications (connectors, cables, color coding etc) for UTP cabling. Fiber Optic cabling. STP cabling.

Design considerations Structured wiring is the way to go. Highest quality connectors should be used. While connecting twisted pair cables to punch down blocks, care must be taken not exceed the bend radius of the cable (otherwise there can be signal leaks, leading to interference). Copper cables should not be run very close to power lines or parallel to them, otherwise there can be interference.

Design considerations(Cont.) The end of the cable should not be untwisted more than needed, as this may result in excessive cross talk. Plenum grade cable must be used where there is a possibility of fire (like area above the suspended ceilings). NEC specifications for fire safety of cable installation should be followed .

Design considerations(Cont.) While splicing fiber optic cable care must be raken to splice it perfectly at right angles. The connection of fiber to the optical connector must be perfect. Fiber should not be bent beyond its bending radius (several inches). Have patch cables as short as possible.

Design considerations(Cont.) Label all the cables and connectors. Maintain an accurate wiring plan. Avoid using already installed telephone cable (since it is not a data grade cable).