01_Introduction to Data Comm - Copy - Copy.ppt

Data Communication &
Computer Networks
Introduction
1.1

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DATA COMMUNICATIONS
•The term telecommunication means communication at a distance.
•Data refers to information presented in whatever form is agreed upon
by the parties creating and using the data. = like .doc, .ppt, .pdf,
.exe, and etc
•Data communications are the exchange of data between two devices via
some form of transmission medium such as a wire cable.
Components
Data Représentation
Data Flow
Topics discussed in this section:

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DATA COMMUNICATIONS
Effective Characteristics of Data Communication
•Delivery (intended Receiver ): the system must deliver data to the correct destination
•Accuracy (unchanged data): The system must deliver the data accurately
•Timeliness: The system must deliver data in a timely manner
•Jitter (uneven delay in audio/video streaming): the variation in the packet arrival time

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Five components of data communication
 Message (text, image, numbers, audio, video)
 Sender(computer, workstation, telephone, camera etc.)
 Receiver
 Transmission Medium(twisted-pair, optical fiber, coaxial cable, radio waves)
 Protocol(set of rules that govern data communication)

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Data Transmission Modes (Ways)
The way of data transfer is called transmission mode.
● Simplex (Ex. Data transmission from computer to monitor)
● Half Duplex (Ex. Data transmission through Walkie-talkie)
● Full Duplex (Ex. Data transmission through Telephone/cable)

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1-2 NETWORKS
A network is a set of devices (often referred to as 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.
Distributed Processing
Network Criteria
Physical Structures
Network Models
Categories of Networks
Interconnection of Networks: Internetwork

 Personal communication
 Email
 Instantaneous communication
 Conferencing
 Tele conferencing
 Videoconferencing
 Audio-conferencing
 Data-conferencing
 Voice over IP
 Phone communication over network wires
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The Uses of a Computer Network
 Simultaneous access to data
 Data files are shared
 Shared files stored on a server
 Software can be shared
 Shared peripheral device
 Printers and faxes are common shares
 Reduces the cost per user
 Devices can be connected to the network
 Print servers control network printing

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NETWORKS
Network Criteria
•Performance:
=> transit time (device to device)
=> response time (enquiry to response)
=> Throughput/Bandwidth: of a channel is the number of bits it can transfer per second
=> delay: is the time that elapses between sending information and the earliest possible
reception of it
•Reliability: Frequency of failure, Time to recover
•Security: Unauthorized Access, Protecting Data

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Types of connections: point-to-point and multipoint
If several devices can use the link simultaneously, it is a spatially shared
connection. If users must take turns, it is a timeshared connection.

 It refers to the way how the network is laid out physically.
 Geometric representation of the relationship of all the links and
linking devices
Mesh Topology
Star Topology
Bus Topology
Ring Topology
Hybrid Topology
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Physical Topology

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A fully connected mesh topology (five devices)
Pros:
• High speed, Little network failure
• Data will always be delivered
• Privacy and Security
• Fault isolation
• Fault identification
Cons:
• Lots of cable: no. of links = n(n-1)/2
for duplex mode
• No. of I/O ports
• Hard to setup (installation)
• Costing
Eg:- Internet is a Mesh Network

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Star Topology
All nodes connect to a hub
•Packets sent to hub
•Hub sends packet to destination
Advantages
•Easy to setup
•One cable can not crash network
Disadvantages
•One hub crashing downs entire network
(Single point of dependency)
•Uses lots of cable
Most common topology

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Bus Topology
 Bus topology
 Also called linear bus
 One wire connects all nodes
 Terminator ends the wires
 Advantages
 Easy to setup(installation)
 Small amount of wire
 Disadvantages
 Slow
 Easy to crash
 Reconnection, signal reflection

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Ring Topology
•Nodes connected in a circle
•Tokens used to transmit data
Nodes must wait for token to send
Advantages
•Time to send data is known/Uni-
directional
•No data collisions
Disadvantages
•Slow
•Lots of cable

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A hybrid topology: a star backbone with three bus networks

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Figure 1.10 An isolated LAN connecting 12 computers to a hub in a closet

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Categories of Networks
LAN
•Privately owned for office, home, buildings etc.
•limited to few kms.
•resource sharing
•generally one type of transmission medium
•speed
Example: Ethernet (CSMA/CD), Local Talk (CSMA/CA) , Wireless LAN, Token Ring
WAN
•Long distance transmission
•either complex (Switched WAN) or simple (point to point WAN)
•e.g. X.25 >> Frame Relay >> ATM, Wireless WAN
•Example- Any telecommunications network that links across metropolitan, regional,
or national boundaries.
Metropolitan Area Network (MAN)
• High speed, DSL, Cable TV network
• DQDB(Distributed Queue Dual Bus) or IEEE 802.6.

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Figure 1.11 WANs: a switched WAN and a point-to-point WAN

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Figure 1.12 A heterogeneous network made of four WANs and two LANs

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1-3 THE INTERNET
The Internet has revolutionized many aspects of our daily
lives. It has affected the way we do business as well as the way
we spend our leisure time. The Internet is a communication
system that has brought a wealth of information to our
fingertips and organized it for our use.
A Brief History
The Internet Today (ISPs)

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Figure 1.13 Hierarchical organization of the Internet

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1-4 PROTOCOLS AND STANDARDS
In this section, we define two widely used terms: protocols
and standards. First, we define protocol, which is
synonymous with rule. Then we discuss standards, which
are agreed-upon rules.
Protocols
Standards
Standards Organizations
Internet Standards

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Protocols (rules)
=>what to communicate, how to communicate and when to communicate
Key Elements of Protocols
1. Syntax: Structure or format of data i.e. the order in which they are presented.
2. Semantics: Meaning of each section of bits
3. Timing : When to send and how fast..

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Standards (agreed upon rules)
Categories of Standards
1. De facto.
By convention or by fact. Not approved by an organized body.
2. De jure.
By Law or by Government. Approved by an organized body.

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2000
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Layering &otocol Stacks

human protocols:
 “what’s the time?”
 “I have a question”
 introductions
… specific msgs sent
… specific actions taken when msgs received, or other events
network protocols:
 machines rather than humans
 all communication activity in Internet governed by protocols
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What’s a protocol?

 protocols define format, order of msgs sent and received among network
entities, and actions taken on msg transmission, receipt
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Protocol
a human protocol and a computer network protocol:
Hi
Hi
Got the
time?
2:00
TCP connection
req.
TCP connection
reply.
Get http://gaia.cs.umass.edu/index.htm
<file>
time

 Essential in creating and maintaining an open and competitive market for
equipment manufacturers
 Guaranteeing national & international interoperability of data &
telecommunication technology & process.
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Standard

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Layered Tasks
An example from the everyday life
Hierarchy?
Services

 To reduce complexity of communication task by splitting it into several
layered small tasks
 Functionality of the layers can be changed as long as the service provided
to the layer above stays unchanged
 makes easier maintenance & updating
 Each layer has its own task
 Each layer has its own protocol
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Why layered communication?

 OSI reference model
 TCP/IP
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Reference Models

 Open System Interconnection
 7 layers
1. Crate a layer when different abstraction is needed
2.Each layer performs a well define function
3.Functions of the layers chosen taking internationally standardized
protocols
4.Number of layers – large enough to avoid complexity
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OSI Reference model

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Seven layers of the OSI model

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Exchange using OSI Model

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The interaction between layers in the OSI model

 Larger bandwidth at lower cost
 Error correction
 Flow control
 Addressing
 Multiplexing
 Naming
 Congestion control
 Mobility
 Routing
 Fragmentation
 Security
 ....
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Issues, to be resolved by the layers

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OSI Layers

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Physical layer
Transporting bits from one end node to the next
- type of the transmission media (twisted-pair, coax, optical fiber, air)
- bit representation (voltage levels of logical values)
- data rate (speed)
- synchronization of bits (time synchronization)
physical
connecti
on

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The physical layer is responsible for movements of
individual bits from one hop (node) to the next.
Note

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Data Link layer
Transporting frames from one end node to the next one
logical
connecti
on
- framing - physical addressing
- flow control - error control
- access control

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Data Link layer
- hop-to-hop delivery-

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Data Link layer
- example-

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The data link layer is responsible for moving
frames from one hop (node) to the next.
Note

01_Introduction to Data Comm - Copy - Copy.ppt

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