Transmission MediaPrepared by: Engr. Maria Diorella A. Paguio

The Basic Idea

Encode data as energy and transmit energy

Decode energy at destination back into data

Energy can be electrical, light, radio, sound, ...

Each form of energy has different properties and requirements for transmission

Data Transmission

Simplex transmission Refers to one way transmission where

one party is the transmitter and the other is the receiver

Example: simple radio

Data Transmission

Half duplex transmission Refers to two way communications

where only one party can transmit at a time

Example: walkie-talkie

Data Transmission

Full duplex transmission Refers to the transmission of data in

two directions simultaneously Example: telephone is a full duplex

device because both parties can talk at once

Transmission Methods

• Data is presented by binary digits, 1 and 0, also called bits. Serial transmission

In serial transmission, bits are sent sequentially on the same channel (wire) which reduces costs for wire but also slows the speed of transmission.

Examples of serial mode transmission include connections between a computer and a modem using the RS-232 protocol.

Transmission Methods

Parallel Transmission In parallel transmission, multiple bits (usually

8 bits or a byte/character) are sent simultaneouslyon different channels (wires,frequency channels) within the same cable,or radio path, and synchronized to a clock.

Examples of parallel mode transmission include connections between a computer and a printer (parallel printer port and cable).

Transmission Media

WIRED TRANSMISSION MEDIA Physical channels or paths that carry

the signal or message from the sender to the receiver

Example: copper wires, twisted pair wires and coaxial cables

Transmission Media

Copper Wires Preferred due to

its low resistance to electric current, which enables signals to travel faster

Transmission Media

To minimize interference, networks use one of two basic wiring types:

Twisted pair Coaxial cable

Transmission Media

Twisted pair wire The most common

form of cable today Used to connect

telephone subscribers to exchanges (switching enters) and wire building)

Used to interconnect PC’s on a Local Area Network (LAN)

Transmission Media

Twisted pair wire Each twisted pair wire is actually two

insulated copper wires twisted around each other.

They are twisted together for the purposes of canceling out electromagnetic interference (EMI) from external sources; for instance, electromagnetic radiation from unshielded twisted pair (UTP) cables, and crosstalk between neighboring pairs.

Transmission Media

Twisted pair wire Other services which makes use of twisted pair

wires: POTS

Public Old Telephone Service Permits voice conversations and digital transmissions with the aid

of a modem Also referred to as PSTN or Public Switched Telephone Network

ISDN Integrated Services Digital Network A digital service

ADSL Asymmetric Digital Subscriber Line Receive data over POTS lines at 1.5 to 9 Mbps

Transmission Media

Twisted pair wire Two forms of twisted pair: Unshielded

and Shielded Twisted PairUTP (unshielded twisted pair) Cable which has no ground shield Two conductors are coated with a plastic

sheath then twisted around each other

Transmission Media

UTP (unshielded twisted pair) Advantages:

High installed base Inexpensive to install Easy to terminate

Disadvantages: Very noisy Limited in distance – 100m Suffer from interference

Transmission Media

STP (Shielded twisted pair)

Shielded twisted pair is a special kind of copper telephone wiring used in some business installations.

An outer covering or shield is added to the ordinary twisted pair telephone wires; the shield functions as a ground.

Twisted pair is the ordinary copper wire that connects home and many business computers to the telephone company.

Maximum Length – 100m

Transmission Media

Coaxial Cable More commonly known as the wiring used for cable

TV Permits high speed data transmission with a

minimum of signal distortion because it provides greater protection from interference than twisted pair

Consists of a single wire surrounded by heavier metal shield which surrounds the center wire uniformly on all sides, making it a more effective barrier to electromagnetic radiation

Maximum length: 200 meters – thin 500 meters - thick

Transmission Media

Coaxial Cable Advantages:

Inexpensive to install

Conforms to standards

Widely used Greater capacity

than UTP

Disadvantages: Limited in distance Limited in number of

connections Costly compared to

twisted pair wires and copper wires

Terminations and connections must be done properly

Utilizes air as channel for carrying the signals in waveform

Utilizes signal generation devices from source and destination endpoints

Transmission Media

WIRELESS TRANSMISSION MEDIA Utilizes air as its channel for carrying

the signals in waveform Utilizes signal generation devices from

the source and destination endpoints

Transmission Media

Microwave System

The transmission of these signals is line of sight, meaning there should be no physical obstacles between the sending and receiving devices

Transmission Media

Microwave System Advantages:

Medium capacity Medium cost Can go long distances

Disadvantages: Noise interference Geographical problems due to line of

sight requirements

Transmission Media

Orbital satellite transmission

Satellite systems are comprised of ground based transmitter and receiver dishes, with an orbital satellite circuit (called a transponder)

Signal are transmitted to the orbiting satellite, which relays it back to another ground station

Transmission Media

Orbital satellite transmission Advantages:

Low cost per user (for PAY TV) High capacity Very large coverage 

Disadvantages: High install cost in launching a satellite Receive dishes and decoders required Delays involved in the reception of the

signal

Transmission Media

Very Small Aperture Terminal (VSAT)

An earthbound station used in satellite communications of data, voice and video signals, excluding broadcast television

Can handle up to 56Kbps

Transmission Media

Very Small Aperture Terminal (VSAT)

Consists of two parts: Transceiver: placed

outdoors in direct line of sight to the satellite

Device: placed indoors to interface the transceiver with the end user’s communications device, such as PC

Transmission Media

HIGH SPEED WIRELESS COMMUNICATION T-carrier system Introduced by the Bell System in the U.S. in

the 1960’s First successful system that supported

digitized voice transmission Entirely digital, using pulse code modulation

and time division multiplexing Uses four wires and provides duplex capability

(two wires for receiving and two for sending at the same time)

Transmission Media

T1-carrier system Dedicated phone connection support data

rates of 1.544Mbits per second Consists of 24 individual channels, each

of which supports 64Kbits per second Popular leased line option for business

connecting to the internet and for internet service providers (ISPs) connecting to the internet backbone

Sometimes referred to as DS1 lines

Transmission Media

E1 The European format for digital

transmission Carries signals at 2Mbps (32

channels at 64Kbps)

Transmission Media

Digital signal X Term for the series of standard

digital transmission rates or levels based on DS0, a transmission rate of 64 Kbps, the bandwidth normally used for one telephone voice channel

Transmission Media

Wireless connections Wireless transceiver provides an

alternative to running a permanent physical line

Used to link these devices: Desktop PC and laptop PC PC and local area network (LAN) PC and mainframe computer Terminal and multiplexer Laptop PC and large printer

Transmission Media

GLASS-BASED TRANSMISSION MEDIA

Fiber optic cable: light pulse Used to transport data as laser generated

pulse of light A single fiber can carry over 32,000 voice

and data transmission, the equivalent of 2.5 billion bits per second

More secure than electronic signals over a wire

Transmission Media

Fiber optic cable: light pulse

Advantages: High capacity Immune to

interference Can go long

distance  Disadvantages:

Costly Difficult to join

Transmission Media

Fiber optic cable: light pulse

COMMON CARRIERS: DEDICATED LINE OR DIAL UP LINE

Dedicated Line A telecommunications

path between two points that is available 24 hours a day for use by a designated user

Physical path owned by the user or rented from a telephone company, in which case it is called a leased line.

Dial - up Line Sometimes called

switched line Telephone connection

in a system of many lines shared by many users

Established and maintained for a limited time duration

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