Chapter 1: Data Communications & Networking: Overview COE 341: Data and Computer Communications...
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Transcript of Chapter 1: Data Communications & Networking: Overview COE 341: Data and Computer Communications...
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