CSE031.Lecture_05.Networks.pdf

Computer and Systems Engineering Department
Ain Shams University, Cairo, Egypt

Chapter 6: Computer Networks
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• A network consists of a collection of computers
and other hardware connected together

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• Resource sharing
To make all programs, data and equipment available to
anyone on the network without regard to the physical
location of the resource.
• High reliability
If some computers go down, others may be able to take
over its work. It is very important for military, air traffic
corporation to continue operating when encounter some
hardware problems.
• Cost saving
• Enhance online communications

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• Electronic mail
• Web-browsing
• Digital libraries
• File transfer
• Video/audio conferencing
• E-commerce

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Networks can be classified by their :
– Topology
The physical arrangement of the network (shape)
• Bus, Ring, Star, Mesh
– Architecture
The way they are designed to communicate
• client-server , peer-to-peer (P2P)
– Size
Networks can be also classified by their size
• LAN , WAN, Man, Pan, Wireless Local Area Network

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Bus Ring Star Mesh

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• All devices on the network are connected to a common cable. Normally, this
cable is terminated at either end, and can never be allowed to form a closed
loop
• Advantages
– Easy to connect a computer or device
– Requires less cable length than other topologies
• Disadvantages
– Data must pass through every computer between sender and receiver which
makes it slower
– Entire network shuts down if there is a break in the main cable.
– Terminators are required at both ends of the main cable.
– Difficult to identify the problem if the entire network shuts down.

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Similar to the bus topology
All the devices on the network are
connected to a common cable which
loops from machine to machine.
After the last machine on the network,
the cable then returns to the first device
to form a closed loop
• Advantages
– Easy to install and wire
• Disadvantages
– Data must pass through every computer between sender and receiver which
makes it slower
– Entire network shuts down if there is a break in the main cable.
– Difficult to identify the problem if the entire network shuts down.

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Each device has its own cable that
connects the device to a common
Hub or switch. Only one device is
permitted to use each port on the hub
• Advantages
– Easy to install and wire
– Easy to add or remove computers and devices
– Easy to detect problems
• Disadvantages
– Requires more cable length than a bus topology
– If the hub fails, nodes attached are disabled
– More expensive than bus topology because of the cost of the hub

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• Every device on the network is physically
connected to every other device on the network.
For n computers, the number of connections is
calculated by the formula: n(n-1)/2. This
provides great performance and reliability
• Advantages
– No traffic problems
– Privacy and security
• Disadvantages
– More cables required
– Expensive Hardware
– Difficult installation and configuration

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Client Server Peer-to-Peer

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It includes two types of devices: clients (PCs, printers, …) and
servers (computers that process client requests)
• Advantages
– Simple network administration
– More scalable
– Data is stored on the servers
• Greater security
• Easy to update data
• Disadvantages
– High traffic
– Network failure = clients are helpless
– Higher costs

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Peer-to-Peer (P2P) computing is the sharing of computer resources
and services by direct exchange between systems
• Advantages
– Easy to install/configure
– Inexpensive
– User is able to control their
own resources
– No need for an administrator
• Disadvantages
– Security problems
– Performance suffers when a computer is accessed
– No centralized data management

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• Networks can be also classified by their size,
which indicates how large the network is.
• Some of the most common types of networks
are:
– PAN - Personal Area Network
– LAN - Local Area Network
– Wireless Local Area Network
– MAN - Metropolitan Area Network
– WAN - Wide Area Network

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• When it receives data from one of its interface, it simply
repeats it on all its outgoing interfaces.
• There is a limit to number of nodes and maximum
distance between nodes.

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• When data is received, it checks the
destination address and either forwards it to
correct interface or drops (filters) it.

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• Max amount of data to be transmitted over a given
time interval
• Depends on
– Media type (microwave, twisted pair, coaxial, optical)
– Coding of information
• Units of measure
– Bits per second (bps)
– Kilo bits per second (Kbps). 1 Kbps =1000 bps
– Mega bits per second (Mbps). 1Mbps = 1000 Kbps
Time
DataSize
BW =
Time
ce
tan
Dis
speed =

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• How long it will take to download a 100 MB file using a
56 Kbps media?
Time
DataSize
BW =
Data Size = 100 MB
= 100 x 1024 x 1024 B (Byte)
= 100 x 1024 x 1024 x 8 b (bit)
BW = 56 Kbps
= 56 x 1000 bps (bit per second)
sec
7
.
14979
1000
56
8
1024
1024
100
BW
DataSize
Time =




=
=
= 249.7 min
= 4.2 hours

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• Calculate the bandwidth of a network, if we
managed to transfer a 50 KB file in 4 msec.
Time
DataSize
BW =
Data Size = 50 KB
= 50 x 1024 x 8 b (bit)
Time = 4 msec
= 4 x 10-3 sec
bps
102400000
10
4
8
1024
50
Time
DataSize
BW 3
=



=
= −
Mbps
Kbps
4
.
102
1000
102400
102400
1000
102400000
=
=
=
=

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• A collection of networks interconnected
and function as a single worldwide
network is known as INTERNET

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• A host number to identify itself to other hosts
• Consists of strings of 32 bits
• E.g. 10111111010101010100000000001100 =
191.85.64.12
• Host Name
– Human-friendly internet addresses
• E.g.
net.shams.edu.eg
or
193.227.1.191

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Convert the following 32-bit Internet address into dotted decimal format:
01011110000101001100001111011100
1) Divide the IP address into four sections
01011110
00010100
11000011
11011100
2) Convert each binary section into a decimal number
01011110 = 64+16+8+4+2 = 94
00010100 = 16+4 = 20
11000011 = 128+64+2+1 = 195
11011100 = 128+64+16+8+4 = 220
3) Write out the decimal values separated by periods
94.20.195.220

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◼ We would go crazy if we would have to remember the
IP addresses of all the web sites that we wanted to
visit
◼ The Domain Name System translates between
domain names and IP addresses of devices
connected to the Internet
– A domain name (a part of the URL) is a unique
alphanumeric name such as gmu.edu

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• Generic top level domains
• .com
• .gov
• .info
• .edu
• .org
• .net, etc.
• Country codes (2 characters code)
• .eg, .jp, .sw, .us, etc.

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Each page of information on the web has a unique
address called the URL at which it can be found
faculty.uscupstate.edu/atzacheva/lecture1.html
Host Name -
The Name of
Web Server
Path to the Web
Page
File Name

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• The postman in the Internet
• On arrival of an IP packet, it makes a routing
decision based on the packet’s destination IP
address.
• Routing decision: to choose the next router to
forward the packet

CSE031.Lecture_05.Networks.pdf

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CSE031.Lecture_05.Networks.pdf