Chapter 1:

Data Communications & Networking: Overview

COE 341: Data and Computer Communications (3-0-3)

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Acknowledgements

Many figures, slides, and course notes were made

available by: Pearson Prentice-Hall (Publishers)

Data & Computer Communications, W. Stallings McGraw-Hill (Publishers)

Data Communications & Networking, B. Forouzan Previous Course Offerings at COE, KFUPM by:

Dr. Marwan Abu-Amara Dr. Taha Landolsi Dr. Ashraf Mahmoud

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Contents Introduction

Merging of computing and communications Integration of various types of data: Text, Pictures, Audio,

Video Communications Model

Main blocks and functionality Communication Tasks

Data Communication Data Communication Networks

Wide Area Networks (WAN) Circuit switching Packet switching

Local Area Networks (LAN) Metropolitan Area Networks (MAN)

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Merging, Integration, and Blurring…. Merging of computing and communications Computers communicate and communication devices (e.g. cell

phones, routers) compute!…

Integration of various types of information: Voice, Video, Text, Pictures, Data Before, they used to be handled by different dedicated networks,

e.g. telephone network for voice only

Blurring of boundaries in computing and communications Microcomputer, Minicomputer, …. Networks: LAN, MAN, WAN, …

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Communication Main purpose of a

communication system is: “Reliable exchange of data between two entities”

3 main areas: Standards and Protocols Networking

Covers technology & architecture of communication networks

Networks categorized into: LANs, MANs & WANs Data Communications (Main Concern of COE 341)

Reliable & efficient data communication over a link Covers signal transmission, transmission media, signal

impairment, signal encoding, synchronization, error detection, data link control (error and flow), multiplexing

HostsRouters, Switches

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Communication over a point-to-point link: A simplified model

Generate Data

Data to Signals

Signals toData

Receive Data

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Simplified Communications Model Source (e.g. PC) Generates data to be transmitted

Transmitter Converts data into transmittable signals (modulation, encoding)

Transmission System (medium + equipment) Carries signals, but introduces attenuation, noise, interference, etc.

Receiver Converts received signals into data (demodulation, decoding)

Destination Takes and uses incoming data

SignalData1101...

Data1101…

Noise, DistortionInterferenceAttenuation

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This deceptive simplicity hides many important tasks! (See pages 11-13 of the textbook for a good description)Interfacing Addressing

Signal generation Routing

Synchronization Recovery

Exchange management: Message formatting

Error detection and correction Security

Error control Network management

Flow control Transmission system utilization

= Tasks covered in some detail in this course

SignalData1101...

Data1101…

Noise, DistortionInterferenceAttenuation

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Simplified Data Communications Model

Information (say ASCII chars) Data (bits) Signal (say 1 KHz signal) Encoding of data g(t) as signals s(t) (Ch. 5) Signal, s(t), should suit the transmission medium (Ch. 3 & 4) Transmission Impairments: attenuation, noise, distortion, etc. (Section 3.3) Is received data, g’, identical to original data, g ? Error detection (Ch. 6) If not, Error correction at RX may help restore g Otherwise, request retransmission of message (Error control), Also flow

control (Ch. 7) Better utilization of link capacity by multiplexing many channels

(Multiplexing) (Ch 8)

Speech, Speech,

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Networking: Why do we need networks? Direct point-to-point communication is not always

possible/practical/efficient: Communicating entities can be too far apart for a single

link A large set of communicating entities (e.g. telephones)

would need impractically large number of connections

(full connectivity for N nodes needs N (N – 1) / 2 links) Not all links would be needed all the time!

Solution is a communication network: Wide Area Network (WAN) Metropolitan Area Network (MAN) Local Area Network (LAN)

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Wide Area Networks (WAN)

Large geographical area, e.g. the world Usually not owned by one organization Relies in part on common carrier circuits Alternative technologies

Circuit switching, e.g. telephone network, ISDN* Packet switching, e.g.:

Frame relay Cell relay (Asynchronous Transfer Mode (ATM))

Example:?

* Integrated Services Digital Network

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WAN Technologies: Circuit Switching Circuit switching was widely used for the public telephone

networks for voice communication. Dedicated path is established before the call (session)

starts and lasts for its duration Switching and transmission resources are committed for

exclusive use of that call throughout its duration OK with telephony, as people keep talking till end of call Not the case with many computer data communication

scenarios (bursty nature), e.g. Web browsing Advantage: Reliable, predictable performance – Delay,

data rate, etc. Once connection is established, end devices appear as if connected directly through a dedicated link

Disadvantage: Inefficient network utilization with computer type data communication

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Simple Switched Computer Network

SwitchingNodes

Link

Computers

End-to-end transmission medium is a network

Host Network Computers (Switches)

SwitchingIs Physical

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WAN Technologies, Contd: Packet Switching (store and forward) No dedicated circuit assigned for the full session duration

Data is split into small chunks (packets), each packet carries the destination address and a sequence number

Packets may travel different routes to the destination arrive out of sequence, experience different delays, etc.

Packets are passed from node to node from source to destination (possibly on multiple routes simultaneously)

At destination, packets are assembled again to form the original message

Used for terminal-to-computer and computer-to-computer data communications

Possible problems for real-time traffic, e.g. telephony?: queuing delay, packet loss, etc. (Voice Over IP)

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Packet Switching

Each packet carries:- Destination address- Sequence number indicating packet position in original message

Even if packets arrive out of sequence, they can still be re-assembled to reconstruct the message correctly at destination

Additional header infoaddressing and control(overhead)

Useful user data(payload)

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Packet Switching (Store & Forward) Networks

1. Datagram (connectionless) Approach:No pre-planned route

2. Virtual Circuit (connection) Approach:Frames follow one pre-planned route

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Evolution of Packet Switching Technology Older packet switching systems (X.25) had a large overhead (redundancy) for handling errors

This limited the useful user data rates to 64 kbps

Now, modern transmission systems are more reliable ( fewer bit errors)

And remaining few errors can be easily handled by higher layers at end systems

Reducing data redundancy and processing at lower layers reduces the overhead, speeds up communication and increases useful (user) data rates

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Newer forms of Packet Switching: 1. Frame Relay

Most overhead for error control is stripped off Variable-length packets (called frames) User data rates increased from 64KB to 2 Mbps

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Newer forms of Packet Switching: 2. ATM Cell Relay

Used on Asynchronous Transfer Mode (ATM) networks

An evolution of frame relay Little overhead for error and flow control Fixed-length packets (called cells):

48 bytes data + a 5-byte header Higher data rates than frame relay:10 Mbps-Gbps Handles data for various types of information, e.g.

speech, video, text, etc.

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Local Area Networks (LANs Vs WANs) Smaller geographical scope A building or a small campus

Usually owned by the same organization that owns the attached devices (e.g. KFUPM)

Data rates are higher (this is made possible by the shorter distances- small total attenuation can afford using higher frequencies, e.g.: Ethernet: 10 Mbps -10 Gbps over 100’s of meters

Originally use a shared broadcast medium, e.g. coaxial cable

But now some switched systems (originally WAN technology) are being introduced (Boundary Blurring!)

Example: The Ethernet (IEEE 802.3 standard)

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Some LAN Topologies:(For further readings, see Part 4 of the textbook)

Star

Ring

Bus

Tree

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Recent LAN Configurations(For further readings: see Part 4 of the textbook) Switched LAN

Switched Ethernet ATM LAN Fibre Channel

Wireless LAN Advantages: Mobility, Ease of installation Example: WiFi (IEEE 802.11 standard)

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Metropolitan Area Networks (MAN) Requirements: Large capacity (data rate)

at low cost and high efficiency to cover the geographical area of say a city

Can be a private or public network Middle ground between LAN and WAN:

Stretching of LAN technology Scaling down of WAN technology

Now also going wireless!: Example: WiMAX (IEEE 802.16 standard)

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Example NetworkingConfiguration:

Two ways of accessing the Internet

- Tel Line- ADSL Line- Cable

Switched LAN Network 2. Through

An accessNetwork

1. ResidentialAccess