7-Transmission Media

DR. JOHN ABRAHAM

UNIVERSITY OF TEXAS PANAM

THEORETICAL BASIS

See previous lesson

Transmission Media

Guided – exact path – physical media Unguided – radio transmission

Taxonomy by forms of Energy

Electromagnetic, light, electrical Use my notes

Background Radiation and electrical Noise

Random electromagnetic radiation (noise). When noise hits metal it produces a small

signal which interferes with data signal

Placing enough metal between noise and communication medium lowers interference.

Twisted pair

Unshielded UTP

Shielded STP

Both wires in a twisted pair is affected equally in case of Noise giving a net difference of 0.

In parallel wires the one closer to the noise source will be affected more, giving a net difference.

Twisted Pair Ten Base-T UTP Connector Type RJ-45 Cat 3 up to 16MHz Cat 4 up to 20MHz Cat 5 up to 100 MHz

More twists per cm and teflon insulation Cat 5e noise immunity 125 mbps Cat 6 – 200 mbps Cat 7 foil shielded around the entire set of wires. 600 Mbpps

Twisted pair wiring scheme

1. Orange white2. Orange3. Green white4. blue5. Blue white6. Green7. Brown white8. Brown

1 White/Orange White/Green 1

2 Orange Green 2

3 White/Green White/Orange 3

4 Blue White/Brown 4

5 White/Blue Brown 5

6 Green Orange 6

7 White/Brown Blue 7

8 Brown White/Blue 8

Problems

cross talk and skin effect Picks up noise from other wires (distortion) Attenuation (reduction of signal strength)

influenced by distances and bit data being transmitted bandwidth of the cable

Twisting - noise will be picked up by both wires which reduce errors also reduces cross talk

Hub is a multiport repeater (operates in Layer1 OSI)

Every transmission from one port is amplified and retransmitted on all other ports

The maximum length of any segment is 100 meters

UTP contd

Using FDM coaxial can carry over 10,000 voice channels

When FDM is used CATV is called Broadband Good for both analog and digital signals Greater attenuation of signals, therefore amplifiers

and repeaters are used frequently. 50 ohm cable is for digital transmission 75 ohm for

TV

Coaxial cable

Single line - multiple connections FDM - frequency division - most widespread

A number of signals can be carried simultaneously if each signal is modulated onto a different carrier frequency

Multiplexing

Each modulated signal requires a certain bandwidth (called a channel)

Channels are separated by bands of unused portions

Broadcast TV - each channel requires 6Mhz. Coaxial cable has 500 MHz bandwidth Voice only requres 4 KHz

Synchronous Time Division Multiplexing Possible when the available data rate of a

medium exceeds the data rate of a digital signal to be transmitted.

Interleave bits or blocks at a time

TDM

Time Division Multiplexing The general alternative to FDM is

time division multiplexing (TDM)

In TDM sources share a medium by ``taking turns''

There are two types of TDM: Synchronous Time Division Multiplexing

(STDM)arranges for sources to proceed in a round-robin

manneralso known as Slotted Time Division Multiplexing

Statistical Multiplexing

Works similar to STDM, but if a given source does not have data to send, the multiplexor skips that source

Most NW use a form of statistical multiplexing because computers do not all generate data at exactly the same rate

Thick 10base5 up to 1650 feet -requires trnsceivers

High Bandwidth - use FDM or TDM Thin Coax 10base2 - up to 607 feet

T-connectors and 50 ohm resitors No more 30 devices on a segment No more than 5 segments in a single LAN Only 3 of these segments may have devices

(90) others are repeaters.

Coaxial cable contd

Greater capacity 2 Gbps over tens of kilometers Repeaters needed only every 8 KM Smaller size & weight Materials used

Plastic (short haul) Glass Fused Silica (best)

Fiber Optics

http://www.datacottage.com/nch/fibre.htm lower attenuation electromagnetic isolation Use LED or ILD

light emitting diode, Injection Laser diode Use Photodiode to detect

PIN photodiode APD photodiode

One - short pulse of light, Zero-absence of light

Fiber contd

Core Cladding

optical properties differ between core and cladding. Cladding has lower refractive index

Jacket to protect against moisture, crushing, etc.

Fiber contd

Light propagates from one end to another in one of the following ways mono mode (straight line)

the source is laser Most expensive

Multimode stepped index the source is LED Bounces of cladding

Multimode graded index The cladding refractive index increases as it moves away from the

core

Fiber contd

Fiber Optic Networks

Taps are difficult Two types of interface

Passive interface one end has an LED or laser diode The other end has photodiode

Active interface incoming light is converted to electric signal Signal is generated to full strength Tap into the signal generator

Wireless Transmission

Radio Microwave Infrared Laser light

Telephone

We skip most of it

The phone system is divided into 2 partsOutside plant

Local loops and trunks

Inside plantswitches

Switching1. Circuit SwitchingA physical connection (circuit) is established between the sender

and the receiver. (Similar to operator plugging in – old days)This path is called an end-to-end path.Time used to find the path adds enormous overhead. Entire

bandwidth is reserved even when there are gaps in communiction.

2. Message SwitchingNo physical path is established.The data is sent to the first switching office.Stored, forwarded later, one hop at a time.

Switching continued.

This is known as store-and-forward network.The message could be typed and saved to punched tape and

forwarded later.There was no block size limit. Therefore, one sender can

monopolize the system.3. Packet SwitchingBlock size has upper limit.No one can monopolize more than a fraction of a sec.Suited for interactive traffic.Each router should have sufficient memory to store data.

Switching continued

In packet switching each packet can be examined and format changed if need to be.

Packets may arrive at different order. Will have to be rearranged.

Types of switches

Hierarchical

Crossbar

Space Division

Time Division

ISDN

Narrow band

Broad band

Narrow Band ISDN

Primary goal was integration of voice and data.

Telephones can be connected to a computer for statistics.

Voice and data can be sent concurrently

Caller ID

ISDN System Architecture

ISDN is a bit pipe

All bits can flow in either direction.

Does not matter where the bit comes from – voice, computer, fax, etc.

Additional bit pipes can be added and combined.

ISDN continued

For each ISDN service a terminating device is need at your location such as NT1.

Up to 8 devices can be added to an NT1, provided you have sufficient bandwidth (pipes).

ISDN interface

Multiple channels can be interleaved by time division multiplexing.

The Channels that are standardized is given on page 142 of the text book.

Basic rate comes 2B and 1 DPrimary rate: 23B +1Hybrid: 1A +1C

N-ISDN

Narrow ISDN focused on 64Kbps channels.

Directed at telephone customers

Big failure

BROADBAND ISDN AND ATM

156 Mbps

This data rate is enough for HDTV

Developed based on ATM technology

ATM is a packet switching technology