Download Computer networks CEN-330

Computer networks
CEN-330
ENG.Wisam oqilat
Computer Science Department
[email protected]
Office hours :8:00-9:00,11:00-12:00,1:00-2:00 SUN.-TUS.-THU
Course Objective

The course is designed to introduce you to the
world of computer networks, so that you could
 know the science being used in running this
network
 Use this knowledge in your professional
field
 The course covers concepts and useful tools
for design and performance analysis of data
communication networks
Reading

Text book:

Data Communications and Networking, 4/e
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
B.A. Forouzan,
McGraw-Hill, 2003,
ISBN 0-07-292354-7.
Reference books:
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Computer Networking, a top-down approach
featuring the Internet (3rd edition),
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J.K.Kurose, K.W.Ross,
Addison-Wesley, 2005,
ISBN 0-321-26976-4.
Computer Networks, A Systems Approach
L. Peterson & Davie
Grading Policy
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lab
Quizzes
First Sessional
Second Sessional
Final Exam
:
:
:
:
:
20 %
10%
15%
15%
40%
Grading Policy is Tentative
Data Communications

Data communications are the exchange of data
between two devices via some form of transmission
medium such as a wire cable.
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Five Components of Data
Communication
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1.
Message
2.
Sender
3.
Receiver
4.
Medium
5.
Protocol
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What’s a protocol?
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A protocol is a set of rules that governs data
communications
Key elements of a protocol are
 Syntax
 Semantics
 Timing
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Direction of data flow
Simplex
Half Duplex
Full Duplex
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Type of connections
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Point-to-point
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Point-to-multipoint
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One-to-one communication
Unicasting
Communication channel shared among nodes
One-to-many
Broadcasting
Multicasting
Multipoint-to-point
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Many-to-one
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Network topologies
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Topology defines the way hosts are
connected to the network
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Network topology issues
a goal of any topology
1. high throughput (bandwidth)
2. low latency
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Terminology
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The throughput or bandwidth of a channel is
the number of bits it can transfer per second
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The latency or delay of a channel is the time
that elapses between sending information and
the earliest possible reception of it
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Categories of Topology
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Mostly used network topologies
bus
mesh
ring
star
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A hybrid topology: a star backbone with three bus networks
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Categories of Network
Generally there are three categories of network
Local Area network (LAN)
Metropolitan Area Network (MAN)
Wide Area Network (WAN)
Category into which a network falls is determined
by its size
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Categories of Network(2)
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Local Area Network (LAN)
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Wide Area Network (WAN)
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A local area network (LAN) is usually privately owned and
links the devices in a single office, building, or campus
A wide area network (WAN) provides long-distance
transmission of data over large geographic area that may
comprise a country, continent or world wide.
Metropolitan Area Network (MAN)
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A metropolitan area network MAN )is a network with a size
between a LAN and a WAN. Usually it is spreaded over a
city or a part of a city
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Protocol

protocols define format, order of msgs sent
and received among network entities, and
actions taken on msg transmission, receipt
a human protocol and a computer network protocol:
Hi
time
TCP connection
req.
Hi
TCP connection
reply.
Got the
time?
Get http://gaia.cs.umass.edu/index.htm
2:00
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<file>
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Layered Tasks
An example from the everyday life
Hierarchy?
Services
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Why layered communication?
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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
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makes easier maintenance & updating
Each layer has its own task
Each layer has its own protocol
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Reference Models
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OSI reference model
TCP/IP
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OSI Reference model
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1.
2.
3.
4.
Open System Interconnection
7 layers
Create a layer when different abstraction is needed
Each layer performs a well define function
Functions of the layers chosen taking internationally
standardized protocols
Number of layers – large enough to avoid
complexity
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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
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Issues, to be resolved by the layers
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Larger bandwidth at lower cost
Error correction
Flow control
Addressing
Multiplexing
Naming
Congestion control
Mobility
Routing
Fragmentation
Security
....
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OSI Layers
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Physical layer
physical
connection
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)
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Note
The physical layer is responsible for movements of
individual bits from one hop (node) to the next.
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Data Link layer
logical
connection
Transporting frames from one end node to the next one
- 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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Note
The data link layer is responsible for moving
frames from one hop (node) to the next.
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Network layer
Not a message
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End-to-End packet delivery
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Needed when 2 devices are attached to
different networks
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What is the network definition here?
Main duties:
1.
2.
3.
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From the original source to a destination
Logical addressing
Routing
Congestion control and QoS
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Source to destination delivery
Data Link
Network
layer
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Network layer
- example -
Network layer addresses
Data Link layer addresses
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Note
The network layer is responsible for the
delivery of individual packets from
the source host to the destination host.
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Transport layer
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Process-to-Process delivery of the entire message
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From the original source to a destination
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Needed when several processes (running programs)
active at the same time
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Main tasks:
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Port addressing
Segmentation and reassembly
Congestion control
Flow control
Error control
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Transport Layer
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Transport layer -an example of a reliable delivery -
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Note
The transport layer is responsible for the delivery
of a message from one process to another.
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Note
The session layer is responsible for dialog
control and synchronization.
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Note
The presentation layer is responsible for translation,
compression, and encryption.
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Application layer
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Enables user to access the network
Provides services to a user
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E-mail
Remote file access and transfer (Telnet, FTP)
Access to WWW (HTTP)
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Note
The application layer is responsible for
providing services to the user.
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OSI Reference Model
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A convenient aid for remembering the OSI
layer names is to use the first letter of
each word in the phrase:
All People Seem To Need Data Processing
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Summary of layers and protocols
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Low-level protocols define the electrical and physical standards
to be observed, bit- and byte-ordering and the transmission and
error detection and correction of the bit stream
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High-level protocols deal with the data formatting, including the
syntax of messages, the terminal to computer dialogue,
character sets, sequencing of messages
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TCP/IP Protocol
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TCP/IP Vs OSI Model
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Four Level of Addresses
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Relationship of Layers & Addresses in TCP/IP
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Note
The physical addresses will change from hop to hop,
but the logical addresses usually remain the same.
A port address is a 16 bit address represented by one
decimal number
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Ethernet Addresses
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The least significant bit of the first byte defines the
type of address.
If the bit is 0, the address is unicast;
 otherwise, it is multicast.
The broadcast destination address is a special case of the
multicast address in which all bits are 1s.
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Example
Define the type of the following destination addresses:
a. 4A:30:10:21:10:1A
b. 47:20:1B:2E:08:EE
c. FF:FF:FF:FF:FF:FF
Solution
To find the type of the address, we need to look at the second
hexadecimal digit from the left. If it is even, the address is unicast. If
it is odd, the address is multicast. If all digits are F’s, the address is
broadcast. Therefore, we have the following:
a. This is a unicast address because A in binary is 1010.
b. This is a multicast address because 7 in binary is 0111.
c. This is a broadcast address because all digits are F’s.
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Example
Show how the address 47:20:1B:2E:08:EE is sent out on
line.
Solution
The address is sent left-to-right, byte by byte; for each
byte, it is sent right-to-left, bit by bit, as shown below:
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QUESTIONS
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