Transcript COE 308: Computer Architecture (T032) Dr. Marwan Abu

COE 341: Data and Computer
Communications (3-0-3)
Term 062
Chapter 1:
Data Communications & Networking:
Overview
Acknowledgements
Many figures, slides, and course notes were made
available by:
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Pearson Prentice-Hall (Publishers)
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McGraw-Hill (Publishers)
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Data & Computer Communications, W. Stallings
Data Communications & Networking, B. Forouzan
Previous Course Offerings at COE, KFUPM by:
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Dr. Marwan Abu-Amara
Dr. Taha Landolsi
Dr. Ashraf Mahmoud
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Contents
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Introduction
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Communications Model
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Merging of computing and communications
Integration of various types of data: Text, Pictures, Audio,
Video
Main blocks and functionality
Communication Tasks
Data Communications
Data Communication Networks
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Wide Area Networks (WAN)
 Circuit switching
 Packet switching
Local Area Networks (LAN)
Metropolitan Area Networks (MAN)
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Merging, Integration, and Blurring….
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Merging of computing and communications
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Integration of various types of information: Voice, Video,
Text, Pictures, Data
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Computers communicate and communication devices (e.g. cell
phones, routers) compute!…
Before, they used to be handled by different dedicated networks,
e.g. telephone network for voice.
Blurring of boundaries in computing and communications
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Microcomputer, Minicomputer, ….
Networks: LAN, MAN, WAN, …
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Communication
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Hosts
Routers, Switches
Main purpose of a
communication system is:
“Reliable exchange of data
between two parties”
3 main areas:
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Networking
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Covers technology
& architecture of communication networks
Networks divided into LANs, MANs & WANs
Standards and Protocols
Data Communications (Main Concern of COE341)
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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
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Communication over a link: A simplified model
Generate
Data
Data to
Signals
Signals to
Data
Receive
Data
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Simplified Communications Model
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Source (e.g. PC)
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Transmitter
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Carries signals, but introduces attenuation, noise, interference, etc.
Receiver
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Converts data into transmittable signals (modulation, encoding)
Transmission System
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Generates data to be transmitted
Converts received signals into data (demodulation, decoding)
Destination
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Takes and uses incoming data
Data
1101...
Signal
Noise, Distortion
Interference
Attenuation
Data
1101…
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Behind this deceptive simplicity hide many important
tasks! (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
= Task covered in some detail in this course
Data
1101...
Signal
Noise, Distortion
Interference
Attenuation
Data
1101…
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Simplified Data Communications Model
Speech,
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Speech,
Information  Data  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 info, m’, identical to original input info, m ? Error detection (Ch. 6)
If not, Error correction may help restore m (Ch. 6) (Not covered)
Otherwise, request retransmission of message (Error control), Also flow
control (Ch. 7)
Better utilization of link capacity by multiplexing many channels
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(Multiplexing) (Ch 8)
Networking
Why do we need networks?
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Point to point communication not usually practical
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Devices can be too far apart for a single link
A large set of devices (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:
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Wide Area Network (WAN)
Metropolitan Area Network (MAN)
Local Area Network (LAN)
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Wide Area Networks (WAN)
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Large geographical area, e.g. the world
Usually not owned by one organization
Relies in part on common carrier circuits
Alternative technologies
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Circuit switching
Packet switching
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Frame relay
Cell relay (Asynchronous Transfer Mode (ATM))
Example:?
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WAN Technologies: Circuit Switching
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Circuit switching is used in the public telephone network
for voice communication.
Dedicated path is established for the duration of the call
(session)
Switching and transmission resources are committed for
exclusive use of the call throughout its duration
OK with telephony, as people keep talking till end of call
Not the case with many computer data situations (bursty)
Advantage: Reliable, predictable performance –
Once connection is established, devices appear as if
connected directly through a dedicated link
Disadvantage: Inefficient utilization with computer type
data communication
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Simple Switched Network
Transmission medium
is a network
Addressing
Switching
Nodes
(Computers)
Link
Routing
Host
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WAN Technologies:
Packet Switching
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No dedicated circuit assigned for the full session duration
Data is split into small chunks (packets), each packet
carries destination address and sequence number
Packets may arrive out of sequence via different routes
Packets are passed from node to node from source to
destination on (possibly 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 telephony? (Voice Over IP)
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Packet Switching
Each packet carries:
- Destination address
- Sequence number indicating its position
in original message
Even if packets arrive
out of sequence, they can still
be re-assembled to reconstruct
the message correctly
at destination
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Packet Switching (Store & Forward) Networks
1. Datagram Approach:
No pre-planned route
2. Virtual Circuit Approach:
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Frames follow one pre-planned route
Evolution of Packet Switching Technology
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Older packet switching systems (X.25) had
large overhead (redundancy) for handling errors
This limited useful user data rates to 64 kbps
Now, modern transmission systems are more
reliable (cause less errors)
And remaining few errors can be easily handled
by higher layers at end systems
Reducing 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
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Most overhead for error control is stripped out
Variable-length packets (called frames)
User data rates up to 2 Mbps
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Newer forms of Packet Switching:
2. Cell Relay
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Used Asynchronous Transfer Mode (ATM)
networks
An evolution of frame relay
Little overhead for error and flow control
Fixed-length packets (called cells)
Higher data rates than frame relay:
10 Mbps to Gbps
Handles data for various types of information, e.g.
speech, video, text, etc.
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Local Area Networks (LANs Vs WANs)
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Smaller geographical scope
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A building or a small campus
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Usually owned by the same organization that
owns the attached devices (e.g. KFUPM)
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Data rates are higher (this is made easier by the
shorter distances- small total attenuation, can afford
using higher frequencies:
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10 Mbps -10 Gbps over 100’s of meters
Now some switched systems and ATM are being
introduced (Boundary Blurring)
The Ethernet: IEEE 802.3
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Some LAN Topologies:
(For further readings: Part 4 of the textbook)
Bus
Ring
Tree
Star or Hub
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Recent LAN Configurations
(For further readings: see Part 4 of the textbook)
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Switched LAN
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Switched Ethernet
May use single or multiple switches
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ATM LAN
Fibre Channel
Wireless LAN
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Advantages: Mobility, Ease of installation
WiFi (IEEE 802.11)
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Metropolitan Area Networks (MAN)
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Requirements: Large capacity (data rate)
at low cost and high efficiency to cover the
area of say a city
Can be a private or public network
Middle ground between LAN and WAN:
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Stretching of LAN technology
Scaling down of WAN technology
Now also going wireless!:
WiMAX (IEEE 802.16)
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Example
Networking
Configuration
- Tel Line
- ADSL Line
- Cable
LAN
Network
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