Introduction to Communication Systems and Networks

Introduction to Communication Systems and Networks

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Communication Systems


Communications Components• Basic components of a

communication system– Communication technologies– Communication devices – Communication channels– Communication software


A Communications Model


Data Communications Model


Communication Technology Applications

voice mail Twitter

e-mailinstant messaging

chat rooms

newsgroups telephony videoconferencing

collaboration groupware global positioning system (GPS)


Communication Technologies - Applications

• Different technologies allowing us to communicate – Examples: Voice mail, fax, email, instant message, chat rooms, news groups, telephony,

GPS, and more• Voice mail: Similar to answering machine but digitized• Fax: Sending hardcopy of text or photographs between computers using fax modem• Email: electronic mail – sending text, files, images between different computer

networks - must have email software – More than 1.3 billion people send 244 billion messages monthly!

• Chat rooms: Allows communications in real time when connected to the Internet • Telephony: Talking to other people over the Internet (also called VoIP)

– Sends digitized audio signals over the Internet – Requires Internet telephone software

• Groupware: Software application allowing a group of people to communicate with each other (exchange data) – Address book, appointment book, schedules, etc.

• GPS: consists of receivers connected to satellite systems – Determining the geographical location of the receiver– Used for cars, advertising, hiking, tracking, etc.


Communication Devices• Any type of hardware capable of transmitting data, instructions, and information

between devices – Functioning as receiver, transmitter, adaptor, converter– Basic characteristics: How fast, how far, how much data!

• Examples: Dial-up modems, ISDN, DSL modems, network interface cards– Dial-up modem: uses standard phone lines

• Converts digital information into analog • Consists of a modulator and a demodulator • Can be external, internal, wireless

– ISDN and DSL Modem: Allows digital communication between networks and computers • Requires a digital modem• Digital is better than analog – why?

– Cable modem: a modem that transmits and receives data over the cable television (CATV) network• Also called broadband modem (carrying multiple signals) • The incoming signal is split • Requires a cable modem

– Network interface cards: Adaptor cards residing in the computer to transmit and receiver data over the network (NIC)• Operate with different network technologies (e.g., Ethernet)


Communication Channels• A channel is a path between two communication devices• Channel capacity: How much data can be passed through

the channel (bit/sec) – Also called channel bandwidth– The smaller the pipe the slower data transfer!

• Consists of one or more transmission media– Materials carrying the signal– Two types:

• Physical: wire cable • Wireless: Air

destination network server

T1 lines

T1 lines

T1 lines

T3 lines


Wireless Transmission Media• Broadcast Radio – Distribute signals through the air over

long distance – Uses an antenna – Typically for stationary locations – Can be short range

• Cellular Radio– A form of broadcast radio used for

mobile communication – High frequency radio waves to transmit

voice or data – Utilizes frequency-reuse


Wireless Transmission Media• Microwaves

– Radio waves providing high speed transmission

– They are point-to-point (can’t be obstructed) – Used for satellite communication

• Infrared (IR) – Wireless transmission media that sends

signals using infrared light- waves - Such as?


Physical Transmission Media

100 Mbps is how many bits per sec?

Which is bigger: 10,000 Mbps, 0.01Tbps or 10Gbps?

Wireless channel capacity:


Networks

• Collection of computers and devices connected together • Used to transfer information or files, share resources, etc. • What is the largest network? • Characterized based on their geographical coverage, speed, capacities • Networks are categorized based on the following characteristics:

– Network coverage: LAN, MAN, WAN– Network topologies: how the computers are connected together – Network technologies– Network architecture


Network coverage• Local Area Networks:

– Used for small networks (school, home, office)– Examples and configurations:

• Wireless LAN or Switched LAN• ATM LAN, Frame Ethernet LAN• Peer-2-PEER: connecting several computers together (<10)• Client/Server: The serves shares its resources between different

clients • Metropolitan Area Network

– Backbone network connecting all LANs– Can cover a city or the entire country

• Wide Area Network– Typically between cities and countries – Technology:

• Circuit Switch, Packet Switch, Frame Relay, ATM– Examples:

• Internet P2P: Networks with the same network software can be connected together (Napster)


LAN v.s WANLAN - Local Area Network a group of

computers connected within a building or a campus (Example of LAN may consist of computers located on a single floor or a

building or it might link all the computers in a small company.

WAN - A network consisting of computers of LAN's connected across a distance WAN can cover small to large distances, using different topologies such as telephone lines, fiber optic cabling, satellite transmissions and microwave transmissions.


Network Topologies • Configuration or physical arrangement in which devices are connected

together • BUS networks: Single central cable connected a number of devices

– Easy and cheap– Popular for LANs

• RING networks: a number of computers are connected on a closed loop – Covers large distances– Primarily used for LANs and WANs

• STAR networks: connecting all devices to a central unit – All computers are connected to a central device called hub– All data must pass through the hub – What is the problem with this? – Susceptible to failure


Network Topologiespersonal

computerpersonal

computerpersonal

computer

personal computer

personal computer

host computer

printerfile server

personal computer

personal computer

personal computer

personal computer


Network Architecture• Refers to how the computer or devices are designed in a network • Basic types:

– Centralized – using mainframes – Peer-2-Peer:

• Each computer (peer) has equal responsibilities, capacities, sharing hardware, data, with the other computers on the peer-to-peer network

• Good for small businesses and home networks • Simple and inexpensive

– Client/Server:• All clients must request service from the server• The server is also called a host• Different servers perform different tasks: File server, network server, etc.

client

client

client

server

laser printer


P2P vs Client-Server

Peer-to-Peer Examples

Peers make a portion of their resources, such as processing power, disk storage or network bandwidth, directly available to other network participants, without the need for central coordination by servers or stable hosts

http://en.wikipedia.org/wiki/File:P2P-network.svg



Any Q?


Introduction: “Everything is Connected to Everything”

• Computer Networking– Internet: A world-wide network connecting millions of

computer networks for the purpose of exchanging data and communications using special rules of communication.

– internet: (lower case i) Any network connecting two or more computer networks.

– The human need to communicate has motivated mankind’s creativity:• Cave dwellers drew pictures on walls.• Smoke signals, drum rhythms passed messages.• American pioneers: Pony express, Wells Fargo.• Alexander Graham Bell: invented the telephone.


Communication Basics of Networks

• Types of connections of computers into networks: Physical versus Wireless connections

– The first type: The Physical Connection. • Physically connect computers together.

– Use of wires or optical cables.– The connections are called network links.

• Three most common physical links:– Twisted pair– Coaxial cable– Fiber-optic cable



• Twisted pair

– Two wires twisted together.• Makes them less susceptible to acting like an

antenna and picking up radio frequency information or appliance noise.

– Telephone company uses twisted-pair copper wires to link telephones.



• Coaxial cable

– Also two wires: • One of the wires is woven of fine strands of

copper forming a tube. • The wire mesh surrounds a solid copper wire

that runs down the center. • Space between has a non-conducting material.• Makes them more impervious to outside noise.



• Fiber-optic cable

– Light is electromagnetic.– Can transmit more

information down a single strand. • It can send a wider set of

frequencies.– Each cable can send

several thousand phone conversations or computer communications.



1. Type of signal communicated (analog or digital).– Analog: Those signals that vary with smooth

continuous changes.• A continuously changing signal similar to that found on

the speaker wires of a high-fidelity stereo system.– Digital: Those signals that vary in steps or jumps

from value to value. They are usually in the form of pulses of electrical energy (represent 0s or 1s).



2. The speed at which the signal is transmitted (how fast the data travels).– In digital systems: Speed is measured in... • Bits per second (bps).

– The number of bits (0’s and 1’s) that travel down the channel per second.

• Baud rate– The number of bits that travel down the channel in a given

interval.– The number is given in signal changes per second, not

necessarily bits per second.



• MODEM - MOdulator DEModulator

– Outgoing: Converts binary data from computer (digital) into telephone compatible signals (analog).

– Incoming: Converts telephone signal (analog) into binary data for the computer (digital).

– Can be an external or internal device (usually a “card”).



• Speed of Signal: Sample bps and baud rate speeds.

300 bps (=300 baud) Painfully slow to the college-level reader1200 bps (=1200 baud) Good reader can keep up2400 bps (=2400 baud) A speed reader would get the general idea9600 bps (=9600 baud) Impossible to read14.4 K bps (not measured in baud) 14,400 bps - 10 to 20 sec. wait for graphics28.8 K bps Minimum desired for WWW

(5 to 10 sec. wait for graphics)56 K bps Efficient speed for WWW.

These speeds are restricted to the maximum speed of the modem at theother end of the connection.



3. The type of data movement allowed on the channel. – Simplex transmission - One way transmission.– Half-duplex transmission - Flows only one way at a time.– Full-duplex transmission - Two-way transmission at the

same time.



4. The method used to transport the data.– Two types of data transmission, each requiring a

different modem.– Asynchronous transmission -

• Information is sent byte by byte.• Cheaper and more commonly used.

– Synchronous transmission - • Data is sent in large blocks rather than in small pieces.• Preceded by special information, concerning error detection

and block size.• These modems are expensive but very fast.



5. Single channel versus multichannel transmission– Channel - A path of a signal.– Single channel - Capable of only sending/receiving

one signal at a time.• Phone line: Single line = single phone call at a time.

– Multichannel - Capable of more than one channel at a time.• Fiber-optic cable, microwaves, Satellite transmissions.



• How is it possible to measure the capacity of communications links? – Bandwidth: Digital

• Number of bits per second (bps) that can be sent over a link.• The wider the bandwidth, the more diverse kinds of information can be sent.• Simplest is voice, most sophisticated is moving videos.

– Bandwidth: Analog• The difference between the highest and lowest frequencies that can be sent

over an analog link (like phone lines).• Measurement is given in hertz (Hz).

– For both: The wider the bandwidth, the more information can flow over the channel.


Thank you

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Introduction to Communication Systems and Networks