Transcript View File - University of Engineering and Technology, Taxila

Lecture # 01
Introduction
Course Instructor:
Engr. Sana Ziafat
Grading Policy
Final Exam:
 Mid term Exam
 Assignments
 Quizzes:
 Lab work

40%
20%
5%
15%
20%
 Quizzes may be announced or unannounced.
 Exams are closed-book and extremely time limited.
 Exams consist of design questions, numerical, maybe
true-false and short answer questions.
TEXT BOOKS

Data Communications and Networking, 4/e


B.A. Forouzan, McGraw-Hill, 2003,
ISBN 0-07-292354-7.
Data and Computer Communication by William
Stallings (7th Edition) Prentice Hall.
Introduction
 Data : Refers to information presented in whatever
form is agreed upon by the parties creating and using
data
 Communication: When we communicate we are
sharing information. This sharing can be remote or
local…. Local face to face and remote at a distance
What is data communication?
 Data communication Exchange of data between two devices via some form of
transmission medium such as wire cable.
 Defined as a subset of telecommunication involving the
transmission of data to and from computers and components
of computer systems.
History of
Telecommunications





Invention of telegraph Samuel Morse – 1837
Invention of telephone- Alexander Graham Bell – 1876
Development of wireless By ??? – 1896
Concept of universal access and growth of AT&T
Divestiture of AT&T—what year??
History of Telecommunications
Continued….
 Telecommunications Act of 1996
 Three main developments that led to the growth of
data communications systems:
 Large-scale integration of circuits reduced the cost and size of
terminals and comm equipment
 Developments of software systems made establishment of
communication networks easy
 Competition among providers of transmission facilities
reduced the cost of data circuits
Fundamental
Characteristics
 The effectiveness of a data communication system
depend on four fundamental characteristics:
 Delivery
 Accuracy
 Timelines
 Jitter (variation in packet arrival time)
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
Simplified Data
Communications Model
Key Communications Tasks
 Transmission system utilization
 Interfacing
 Signal generation
 Synchronization
 Exchange management
 Error detection and correction
 Addressing and routing
 Recovery
 Message formatting
 Security
 Network management
Data REPRESENTATION
 Data can be represented as
1. Text
2. Numbers
3. Images
4. Audio
5. Video
Direction of data flow
Simplex
Half Duplex
Full Duplex
Before looking inside a computer network,
first agree on what a computer network is
Computer network ?
Specialized to
handle:
 Set of serial lines to
attach terminals to
mainframe ?
 Telephone network
carrying voice traffic ?
 Cable network to
disseminate video signals
?
Keystrokes
Voice
Video
Networks
 Potential of networking:
 move bits everywhere, cheaply, and with desired
performance characteristics
 Network provides “connectivity”
What
is
“Connectivity”
?
 Direct or indirect access to every other node in the
network
 Connectivity is the magic needed to communicate if
you do not have a direct pt-pt physical link.
 Tradeoff: Performance characteristics worse than true physical link!
A Network
A network can be defined recursively as
two or more nodes connected by a physical link
Or
two or more networks connected by one or more
nodes
Network Hardware
Transmission Technology
Broadcast/ Multipoint
Network
Point – To – Point
Network
Single communication channel
that is shared by all the
machines on the network.
Many connections between
individual pairs of machines
All the others receive “Packets”
in certain contexts, sent by any
machine.
A packet may have to visit
one or more intermediate
machine.
An address field within the
packet specifies for whom it is
intended.
Routing algorithms play an
important role in PTP
networks.
Multicasting: transmission to a
subnet of the machines.
Types of connections: point-to-point and
multipoint
Simplified Network Model
Building Blocks
 Nodes: PC, special-purpose hardware…
 hosts
 switches
 Links: coax cable, optical fiber…
 point-to-point
 multiple access
…
Switched
Networks
A network can be defined recursively as...

 two or more nodes
connected by a link
 white nodes (switches)
implement the
network
 colored nodes (hosts)
use the network
Switched
Networks
A network can be defined recursively as...

 two or more networks
connected by one or more
nodes: internetworks
 white nodes (router or
gateway) interconnects
the networks
 a cloud denotes “any type
of independent network”
Switching Strategies

Circuit switching:
carry bit streams
a.
b.
c.
d.
establishes a dedicated
circuit
links reserved for use by
communication channel
send/receive bit stream
at constant rate
example: original
telephone network
• Packet switching:
store-and-forward
messages
a. operates on discrete
blocks of data
b. utilizes resources
according to traffic
demand
c. send/receive messages
at variable rate
d. example: Internet
Networks: key issues
 Network criteria
 Performance
Transit time
 Throughput
 Delay
 Reliability
 Data transmitted are identical to data received.
 Measured by the frequency of failure
 The time it takes a link to recover from a failure
 Security
 Protecting data from unauthorized access

Terminology
 The throughput or bandwidth of a channel is
the number of bits it can transfer per second
 The latency or delay of a channel is the time
that elapses between sending information and
the earliest possible reception of it
Network topologies
 Topology defines the way hosts are connected to the
network
Network topology issues
A goal of any topology
1. high throughput (bandwidth)
2. low latency
Categories of Topology
devices)
Advantages & disadvantages of
mesh
topology

Advantages
- Dedicated links eliminate the traffic problem
-Secure communication
-Ease of fault identification & fault Isolation
-Robust
Disadvantages
-Large number I/O ports & cabling required
-Installation & reconfiguration is difficult
-Wiring can be greater than available space
-Expensive
A star topology connecting four stations
Advantages & disadvantages of star
topology
 Advantages
-Less expensive than mesh topology
-Installation & reconfiguration are easy
-Robust
- Ease of fault identification & fault Isolation
-Required less cabling than mesh topology
 Disadvantages
-Dependency of whole topology on single point
Application: High Speed LAN
A bus topology connecting three stations
Advantages & disadvantages of bus
topology
 Advantages
-Ease of installation
-Required less cabling
 Disadvantages
-Difficult reconnection &fault isolation
-A fault or break stops all transmission
A ring topology connecting six stations
Advantages & disadvantages of bus
topology
Advantages
-Ease of installation & reconfiguration
Disadvantages
-A break in ring can disable the entire link
A hybrid topology: a star backbone with three bus networks
What next ?
 Hosts are directly or indirectly connected to each
other
 Nodes must be able to say which host it wants to
communicate with
Addressing and Routing
 Address: byte-string that identifies a node
 usually unique
 Routing: forwarding decisions
 process of determining how to forward messages to the
destination node based on its address
 Types of addresses
 unicast: node-specific
 broadcast: all nodes on the network
 multicast: some subset of nodes on the network
Wrap-up
 A network can be constructed from nesting of
networks
 An address is required for each node that is
reachable on the network
 Address is used to route messages toward
appropriate destination
LAN, WAN & MAN
 Network in small geographical Area (Room, Building or a
Campus) is called LAN (Local Area Network)
 Network in a City is call MAN (Metropolitan Area Network)
 Network spread geographically (Country or across Globe) is
called WAN (Wide Area Network)
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
Local Area Networks (Cont.)
NETWORKS
LAN
MAN
WAN
INTERNET
LAN CHARACTERISTICS
Size
Restricted in
Size
Transmission Technology
Single Cable
10 to 100 Mbps
Low delay (ms)
Very few Errors
Megabits/Sec. (Unit)
Topology
BUS (Ethernet)
Ring (Token ring)
MAN




Metropolitan Area Network
Support data and voice
No switching elements
Two unidirectional buses to which all the computers are
connected.
 Each bus has a head-end, a device that initiates
transmission activity.
 Traffic that is destined for a computer to the right of the
sender uses the upper bus, traffics to the left uses the lower
one.
Wide Area Networks
 Large geographical area
 Alternative technologies
 Circuit switching
 Packet switching
 Frame relay
 Asynchronous transfer mode (ATM)
Internet
 Collection of interconnected networks.
 Example: A collection of LAN’s connected by a WAN.
Applications
 E-mail
 Searchable Data (Web Sites)
 E-Commerce
 News Groups
 Internet Telephony (VoIP)
 Video Conferencing
 Chat Groups
 Instant Messengers
 Internet Radio
Research areas in Networking
 Routing
 Security
 Ad-hoc networks
 Wireless networks
 Protocols
 Quality of Service
…
COURSE OUTLINE
 Network Models
 Encoding Schemes
 Bandwidth Utilization
 Different types of transmission medium
 Error detection & Correction
 IP addressing …
Readings
 Chapter 1: 1.1, 1.2
 Data & Computer Communication seventh Edition , By
William Stallings
 Chapter 1: 1.1, 1.2 (B. A Forouzan)
 Data Communications and Networking, By Behroz A
Forozun
Q&A