Transcript William Stallings Data and Computer Communications

Text book:
Data and Computer Communications
William Stallings
Reference Books:
1- computer networkes,Andrew S.Tanenbaum
2- Data Communications and Networking, 3rd
Edition, Behrouz A. Forouzan
Chapter 1
Introduction to networking
What is the computer network
Network
• A set of devices (nodes) connected by communication links.
• A node can be a
• Computer
• Printer, or
• Any other device capable of sending and/or receiving
data generated by other nodes on the network.
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Why Study Data Communication &
Networking?
 Because Data Communication & Networking are changing the
way we do business and the way we live
 Require immediate access to accurate information
 Database, online shopping
 Enable long distance communication
 Internet, IP phone
 Access variable of information such as text, voice and
image
 Email, messenger, video conference
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What is Data Communication?
 Communications
 The exchange of information between individuals
using a common set of symbols, signs, behavior or
language.
 Data
 Information presented in whatever forms is agreed
upon by the parties creating and using data
 Data communications
 The exchange of data between two devices via some
form of transmission medium such as a wire cable
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A Communications Model
 Source
 generates data to be transmitted
 Transmitter
 Converts data into transmittable signals
 Transmission System
 Carries data
 Receiver
 Converts received signal into data
 Destination
 Takes incoming data
Simplified Communications
Model - Diagram
A Data Communication Model
 Message
 Sender
 Receiver
 Medium
 Protocol
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Simplified Network Model
Key Communications Tasks
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Transmission System Utilization
Interfacing
Signal Generation
Synchronization
Exchange Management
Error detection and correction
Addressing and routing
Recovery
Message formatting
Security
Network Management
Simplified Data
Communications Model
Networking
 Point to point communication not usually
practical
 Devices are too far apart
 Large set of devices would need impractical number
of connections
 Solution is a communications network
TYPE OF CONNECTION
 Point to point
 A dedicated link is provided
between two devices
 Multipoint
 More than two specific
devices share a single link
Point – to – point connection
Multipoint connection
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Broadcast Networks
Types of transmission
technology
• Broadcast links
• Point-to-point links
Distributed Processing
A task is divided among
multiple computers
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Broadcast Networks (2)
Classification of interconnected processors by
scale.
Network Criteria
 Performance – affected by
1. # users
2. Type of medium
3. HW/SW
 Reliability – measured by
1. Freq of failure
2. Recovery time
3. Catastrophe vulnerability
 Security
1. Protection from unauthorized access
2. Viruses
{Homework; difference between virus &
worm}
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Categories of Networks
Based on
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Ownership
Distance covered
Physical architecture
Control
Network Hardware
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Local Area Networks
Metropolitan Area Networks
Wide Area Networks
Wireless Networks
Home Networks
Internetworks
Internetworks
 Connection of two or more networks
 Internet vs. internet
 internet
 Two or more networks can communicate with each other
 Internet
 A collaboration of more than hundreds of thousands interconnected networks
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The Internet
Collaboration of more than hundreds of
thousands of interconnected networks
1969 – started as ARPAnet, a small network of
connected computers
1972 - Cerf and Khan – packet delivery and
Transmission Control Protocol (TCP)
Shortly thereafter – evolution of TCP/IP
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Wide Area Networks
Large geographical area
Crossing public rights of way
Rely in part on common carrier circuits
Alternative technologies
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Circuit switching
Packet switching
Frame relay
Asynchronous Transfer Mode (ATM)
Local Area Networks
Smaller scope
 Building or small campus
Usually owned by same organization as
attached devices
Data rates much higher
Usually broadcast systems
Now some switched systems and ATM are being
introduced
Metropolitan Area Networks
A metropolitan area network based on cable TV.
Wireless Networks
Categories of wireless networks:
• System interconnection
• Wireless LANs
• Wireless WANs
Wireless Networks (2)
(a) Bluetooth configuration
(b) Wireless LAN
Wireless Networks (3)
(a) Individual mobile computers
(b) A flying LAN
Wireless LANs
(a) Wireless networking with a base station.
(b) Ad hoc networking.
Wireless LANs (2)
The range of a single radio may not cover the
entire system.
Wide Area Networks
Relation between hosts on LANs and the subnet.
Circuit Switching
Dedicated communications path established for
the duration of the conversation
e.g. telephone network
Packet Switching
Data sent out of sequence
Small chunks (packets) of data at a time
Packets passed from node to node between
source and destination
Used for terminal to computer and computer to
computer communications
Frame Relay
Packet switching systems have large overheads
to compensate for errors
Modern systems are more reliable
Errors can be caught in end system
Most overhead for error control is stripped out
Protocols
Used for communications between entities in a
system
Must speak the same language
Entities
 User applications
 e-mail facilities
 terminals
Systems
 Computer
 Terminal
 Remote sensor
Protocol Architecture
Task of communication broken up into modules
For example file transfer could use three
modules
 File transfer application
 Communication service module
 Network access module
Asynchronous Transfer Mode
ATM
Evolution of frame relay
Little overhead for error control
Fixed packet (called cell) length
Anything from 10Mbps to Gbps
Constant data rate using packet switching
technique
Protocols and Standards
Why do we need them?
Protocol
 set of rules that govern data communication
 defines what, how, and when
 Key elements
 Syntax
 Semantics
 timing
Standard
 provides a model for development
 allows for interoperability
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OSI Model
Open Systems Interconnection
Developed by the International Organization for
Standardization (ISO)
Seven layers
A theoretical system delivered too late!
TCP/IP is the de facto standard
Standards
Required to allow for interoperability between
equipment
Advantages
 Ensures a large market for equipment and software
 Allows products from different vendors to
communicate
Disadvantages
 Freeze technology
 May be multiple standards for the same thing
Key Elements of a Protocol
Syntax
Data formats
Signal levels
Semantics
Control information
Error handling
Timing
Speed matching
Sequencing