This document provides information about a computer networks course including details about the lecturer, course content, objectives, and prerequisites. The course covers 12 weeks of material on topics ranging from the history of computer networks and the TCP/IP protocol stack to IP routing, data link layer services, and wireless networking principles. Assessment includes two term exams, a final exam, and a lab component. The goal is for students to gain an understanding of major computer network components, how the Internet works, and networking protocols at each layer of the TCP/IP model.

1. Course code: COE351
Course title : Computer Networks
PART: 1
Prof. Taymoor Mohamed Nazmy
Dept. of computer science, faculty of computer science, Ain Shams uni.
Ex-vice dean of post graduate studies and research Cairo, Egypt
1

2. About the lecturer
- Prof. of computer science since 2006,
- Director of Ain Shams information network,
- Vice dean of post graduate studies and research,
- Vice dean of environmental and social affairs,
- Member in editorial board of many Int. journals,
- Member in Scientific committee of many int. conferences
- Executive chair of int. conf. on information and intelligent systems,
- Published more than 60 scientific papers in int. journals and
conference,
Supervised more than 20 master and Ph. D thesis.
2

3. ntaymoor19600@gmail.com
3

4. About the course
• The materials of this course were collected from many resources, include the
reference book, other books, online courses, presentations, and web sites.
• There are many details will be given to simplify topics in this course, however at
the end of the course the most important topics will be highlighted.
• The delivered materials through this presentation is your main resource,
• This presentation will be delivered to you.
• There will be 2 term exams 60%
• The final exam 40%
• Lab 100 mark
• The exam will include subjective and objective questions,
4

5. Course Description
•
Week 1 : Introduction to Computer Networks – History, Circuit Switching and Packet
Switching
• Week 2 : TCP/IP Protocol Stack – Basic Overview
• Week 3 : Application Layer Services (HTTP, FTP, Email, DNS)
• Week 4 : Transport Layer Primitives – Connection Establishment and Closure
• Week 5 : Flow Control and Congestion Control at the Transport Layer
• Week 6 : Transmission Control Protocol – Basic Features, TCP Congestion Control
• Week 7 : Network Layer Primitives – IP Addressing
• Week 8 : IP Routing – Intra Domain Routing Protocols, Inter Domain Routing Protocols
Week 9 : IP Services – SNMP, ARP
• Week 10 : Data Link Layer Service Primitives – Forwarding, Flow Control, Error Control
• Week 11 : Media Access Control - Channel Access Protocols, Framing
• Week 12 : End Principles of Computer Networks
• Textbook:
• Computer network: Atop down approach featuring the internet. By James F. Kurose. Et. Al.,
6th edition, Addison Wesley, 2012.
5

6. Course Objectives
• Upon successful completion of this course, students should be able
to:
• Describe the major computer networks components
• Describe how Internet works
• Understand the TCP/IP layers
• Understand the application layer
• Understand how HTTP, FTP, Email, Web, and DNS work
• Understand the transport layer
• Understand TCP, and UDP
• Describe the network layer
• Describe IPv4
• Understand routing and routing algorithms
• Understand data link layer protocols
6

7. Preface

8. Computer network course
• Is one of the most important courses that is
delivered to all departments in faculties of
computer science and engineering, it is also, one
of the courses that related directly to the job
market.
• In generals it consists of:
• A set of terminologies, and concepts,
• Software,
• Technologies.

9. The Computer Networks &
Communications as a Department
• The Computer Networks & Communications
Department, provides education in Computer
Technology/Information Technology that
pertains to local and wide area networks,
Network administration, IT Help
Desk/Technical Support, and Cisco Systems
Networking.

10. The most powerful company in
enterprise networking
• Cisco:
• Cisco remains the biggest single player in enterprise
networking. The company offers one-stop shopping for almost
anything you could need for your network and ensures that its
products play nicely with each other. Its revenue in 2017 was
$ 48.0 billion

11. Some of cisco products
• Networking
• Switches
• Routers
• Wireless
• Network Management
• Interfaces & Modules
• Optical Networking
• Software-Defined Networking
• Software
• IOS & NX-OS
• Cisco ONE for Access
• Cisco ONE for WAN
• Cisco ONE for Data Center
Networking
• Cisco ONE for Data Center Compute
and Cloud
• Wireless and Mobility
• Access Points
• Outdoor and Industrial Access Points
• Controllers
• Data Center
• Servers - Unified Computing
• Data Center Management and
Automation
• Data Center Security
• Data Center Switches
• Hyperconverged Infrastructure
• Storage Networking
• Virtual Networking

12. Best Computer Networking Certifications 2018
• Those who are serious about their careers should consider one or more of these best-of-
breed networking certifications to set themselves apart from the competition. Cisco
Certifications are the list of the Certifications offered by Cisco Systems, examples of those
certificates are:
• -CCNP: Cisco Certified Network Professional
• The Cisco Certified Network Professional (CCNP) takes aim at platforms and products
from a leading networking equipment vendor found at most communications and internet
service providers
• CCNP: Cloud
• CCNP: Collaboration
• CCNP: Data Center
• CCNP: Routing and Switching
• CCNP: Security
• CCNP: Service Provider
• CCNP: Wireless
• CCIE: Cisco Certified Internetwork Expert:
• JNCIE-ENT: Juniper Networks Certified Enterprise Routing and Switching Expert
• WCNA: Wireshark Certified Network Analyst

13. Certification Paths
Level Architect
Routing
and
Switching
Design Cloud
Collabora
tion
Cybersec
urity
Operation
s
Data
Center
Industrial
/ IoT
Security
Service
Provider
Wireless
Expert
CCAr
Architect
(CCDE
previous)
CCIE
Routing
and
Switching
CCDE -
CCIE
Collaborati
on
-
CCIE Data
Center
-
CCIE
Security
CCIE
Service
Provider
CCIE
Wireless
Professiona
l
-
CCNP
Routing
and
Switching
CCDP
CCNP
Cloud
CCNP
Collaborati
on
-
CCNP
Data
Center
-
CCNP
Security
CCNP
Service
Provider
CCNP
Wireless
Associate -
CCNA
Routing
and
Switching
CCDA
CCNA
Cloud
CCNA
Collaborati
on
CCNA
CyberOps
CCNA
Data
Center
CCNA
Industrial
CCNA
Security
CCNA
Service
Provider
CCNA
Wireless
Entry CCENT, CCT

14. Free ccna course
• https://study-ccna.com/
• Cisco training courses
• https://www.cisco.com/c/en/us/training-
events/training-certifications/training-
catalog/course-selector.html

15. The networking jobs in, wired, wireless, or mobile
network, might include:
• Network Security Specialist
• Cloud Networking Architect
• Networking Research and Development Specialist
• Wireless Networking Engineer
• Wireless Infrastructure and Mobility Specialist
• Mobility Solutions Architect
• VoIP Engineer
• Telecom Project Manager
• Data Center Networking Specialist
• Networking Sales Specialist
• Networking Account Manager
• Networking Consultant
• Networking Program Manager

16. The Future of Networking
• So many changes in the next few decades will happened. Here
are a few examples:
• IPv6 finally takes over: Experts predicted the demise of IPv4
• Domain Name System (DNS), to eventually disappear as Web
browsers become capable of navigating to Web sites purely
through voice recognition, eye movements and/or touch
interfaces.
• As people owning hundreds of wearable and mobile devices
that need to communicate both inside in the home and away,
devices will all communicate with each other and the Internet
directly, without fixed router.

18. Supported materials
• https://www.geeksforgeeks.org/computer-
network-tutorials/

19. Lets start our Course:
Computer Networks, brief history of
internet & internet architecture
19

20. • A computer network, or data network, is a digital
telecommunications network which allows nodes to share
resources.
• In computer networks, computing devices exchange data with
each other using connections (data links) between nodes.
These data links are established over cable media such as
wires or optic cables, or wireless media such as WiFi.
Computer Networks
20

21. • Network devices including switches and routers use a
variety of protocols and algorithms to exchange
information and to transport data to its intended
endpoint.
• Every endpoint (sometimes called a host) in a network
has a unique identifier, often an IP address or a Media
Access Control address ( MAC address), that is used to
indicate the source or destination of the transmission.
• Endpoints can include servers, personal computers,
phones and many types of network hardware.
21

22. • Networks may use a mix of wired and wireless
technologies. Network devices communicate
through a wired or wireless transmission
medium.
• In wired networks, this may consist of optical
fiber, coaxial cable or copper wires in the form
of a twisted pair.
22

23. A closer look at network structure:
 network edge:
 hosts: clients and servers
 servers often in data centers
 access networks,
physical media: wired,
wireless communication
links
 network core:
interconnected routers
network of networks
mobile network
global ISP
regional ISP
home
network
institutional
network
1-2323

24. 24
The network edge:
• end systems (hosts):
– run application programs
– e.g., WWW, email
– at “edge of network”
• client/server model
– client host requests, receives
service from server
– e.g., WWW client (browser)/
server; email client/server
• peer-peer model:
– host interaction symmetric
– e.g.: teleconferencing

25. Typical example of computer network
25

26. Basic computer network components
• Servers - Servers are computers that hold shared files, programs, and the
network operating system. Servers provide access to network resources to
all the users of the network. There are many different kinds of servers, and
one server can provide several functions. For example, there are file
servers, print servers, mail servers, communication servers, database
servers, fax servers and web servers.
• Clients - Clients are computers that access and use the network and shared
network resources. Client computers are basically the customers(users) of
the network, as they request and receive services from the servers.
• Transmission Media - Transmission media are the facilities used to
interconnect computers in a network, such as twisted-pair wire, coaxial
cable, and optical fiber cable. Transmission media are sometimes called
channels, links or lines
26

27. • Shared data - Shared data are data that file servers provide to
clients.
• Shared printers and other peripherals - Shared printers and
peripherals are hardware resources provided to the users of the
network by servers.
• Network Interface Card - Each computer in a network has a
special expansion card called a network interface card (NIC).
• The NIC prepares(formats) and sends data, receives data, and
controls data flow between the computer and the network.
27

28. • Local Operating System - A local operating system allows
personal computers to access files, print to a local printer.
Examples are MS-DOS, Unix, Linux, Windows 2000,
Windows 10.
• Network Operating System - The network operating system
is a program that runs on computers and servers, and allows
the computers to communicate over the network.
• Hub - Hub is a device that splits a network connection into
multiple computers. It is like a distribution center.
28

29. • Switch - Switch is like a Hub but built in with advanced
features. It uses physical device addresses in each incoming
messages so that it can deliver the message to the right
destination or port.
• Router - When you have two distinct networks or want to
share a single internet connection to multiple computers, we
use a Router. In most cases, recent routers also include a
switch which in other words can be used as a switch. There are
two types of Router: wired and wireless.
29

30. 30
The internet
An internet is two or more networks that can
communicate with each other. The most notable internet is
called the internet, composed of hundreds of thousands of
interconnected networks.
Private individuals as well as various organizations such
as government agencies, schools, research facilities,
corporations, and libraries in all the world countries use
the Internet.

31. Web or Internet?
 They are not the same things.
 The Internet is a collection of computers or
networking devices connected together.
– They have communication between each other.
– Decentralized design that there is no centralized body
controls how the Internet functions.
 The Web is a collection of documents that are
interconnected by hyper-links.
– These documents are accessed by web browsers and
provided by web servers. 31

32. What is the Intranet
 Intranet: An intranet is a private network that is
contained within an enterprise.
 It may consist of many interlinked local area
networks and also use leased lines in the wide area
network.
32

33. Brief history of the internet
There have been 3 main phases in the funding
of the Internet in the US
 ARPA phase 1969-1990
 NSF phase 1990-1995
 Commercial phase 1995-present
33

34. ARPA Phase
• Starting in 1969, the DoD (department of Defense)
funded the early growth of the Internet by supporting
the ARPANet.
• ARPANet traffic was supposed to be limited to
defense and research purposes only
• By the middle of the 1980’s other players started to
build around the ARPAnet
34

35. ARPA Phase
• 1984: NSF (National scientific foundation) starts
contracting for the building of a national backbone
(56kbps) that connects research universities.
• At this time, other government agencies, and some
commercial agencies and academic institutions begin
building regional networks
35

36. ARPA Phase
• By the end of the 1980’s, the ARPANet was no
longer the core of the Internet in the US
• In 1990, ARPA decommissioned the ARPANet
36

37. NSF Phase
• By 1990, the NSF is the dominant backbone
internet provider
• In 1990, the acceptable use policy is relaxed,
allowing more commercial use.
• November, 1990 – first WWW page
37

38. NSF Phase
• In 1994, NSF awarded contracts to replace and
manage its backbone network
• Part of the replacement includes 4 Network
Access Points (NAP) to be built by
• San Francisco, Chicago, New York, DC
38

39. Commercial Phase
• Starting in 1995, the funding for the physical
Internet has become a mostly commercial
venture
• However, in 1997 NSF approved funding for a
new high-speed research network – Internet 2
39

40. ‘Network of networks’
• Every computer connected to the Internet is part of a network,
even the one in your home
• For example, when you connect to your ISP (Internet service
provider), you become part of their local network
• The ISP will then connect to a larger network and become part
of their national network
• Next comes the global network that lets you connect to
computers across the planet
• That’s why the Net is ‘a network of networks’
40

41. Internet’s Hierarchical Structure
• The whole internet connections of the network can
be considered to be consists of 3 tiers (levels):
• Tier 1 Internet Service Providers (ISPs)
– Provide services to their customers and sell access to tier 2 and 3 ISPs
• Tier 2 ISPs
– Connect with tier 1 ISPs
– Provide services to their customers and sell access to local ISPs
• Tier 3 ISPs
– Connected to tier 1 or 2 ISPs
– Sell access to individuals
41

42. 42
Internet’s Hierarchical Structure
backbone
ISPs, T1
regional
ISPs, T2
local ISPs,
T3
•enterprise
•campus, ...
end systems
•hosts, servers
•pdas, mobiles

43. Internet Backbones
• Backbone circuits for national ISPs
– OC-48 and OC-192 (10 Gbps) becoming more common.
– OC-768 (40 Gbps) and use OC-3072 (160 Gbps) is in experiment
stage.
• Aggregate Internet traffic
– Growing rapidly
– Internet traffic was about 80 Terabits per second (Tbps) in 2011.
• Requiring larger and larger switches
43

44. • A PoP just means an access point to the Internet, where an ISP has
hardware
• So your ISP will have a POP in your local area since your ISP uses
hardware in the street cabinets and local exchanges or data centres
• In fact, an ISP will have several POPs in an urban area to give good
access
Point of Presence (PoP)

45. • A NAP is where different networks interconnect or
join
• Such as your home network onto your ISP’s
network
• Then the ISP’s network onto the Internet backbone
• A NAP is a bit like an airport for data, where
different carries connect
Network Access Point (NAP)

46. Sample Diagrams
POP
NAP
Internet
A place
where your
ISP puts its
hardware to
get you
connected
Where
networks
join, so you
go from local
to national to
global access

47. Basic Internet Architecture
47

48. 48

49. 49
Network core
Switching
The passage of a message that may send from a source to a destination involves
many decisions.
When a message reaches a connecting device, a decision needs to be made to
select one of the output ports through which the packet needs to be send out.
In other words, the connecting device acts as a switch that connects one port to
another port.

50. Switched network
 Switched network: consists of a series of interlinked
nodes called switches
 Switching devices: devices capable of creating a
temporary connections between two or more devices
linked to the switch and can forward the packet to the
next link along the path to its destination.
router
End system
50

51. Switching
• Networks have interconnecting devices, which receives data
from directly connected sources, stores data, analyze it and
then forwards to the next interconnecting device closest to the
destination. Switching can be categorized as:
51

52. 52
PACKET SWITHING
The network layer is designed as a packet-switched network.
This means that the packet at the source is divided into
manageable packets, normally called datagrams. Individual
datagrams are then transferred from the source to the
destination.
The received datagrams are assembled at the destination
before recreating the original message. The packet-switched
network layer of the Internet was originally designed as a
connectionless service, but recently there is a tendency to
change this to a connection-oriented service.

53. Packet Switching
• The entire message from a source is broken down into smaller
chunks called packets.
• The switching information is added in the header of each
packet and transmitted independently.
• There are two types of packet-switched network, A
connectionless, and a connection-oriented packet switched
network.
• packet transmitted in a connectionless mode is frequently
called a datagram
•
53

54. 54
Packet Switching
Original Message
Computer X
Packet
Switch
A
Packet
Switching
Decision
B
C
Computer Y
F
ED
1. Break message into
Smaller packets
(also known as frames)
2. Route packets individually;
Packet switches along the way
Make decisions about the packet

55. 55
A connection-oriented packet switched network
4 3 2 1
4
3
2
1
4 3 2 1 4 3 2 1
55

56. 56
Sender Network
Network
ReceiverOut of orderR3
R4
R5
R1 R2
Aconnectionless
packet-swtiched network
A connectionless packet-switched network
4 3 2 1
1
2
3
4
2
3 3
1
4 43 21
56

57. Circuit Switching
• When two nodes communicate with each other over a dedicated
communication path, it is called circuit switching.
• There 'is a need of pre-specified route from which data will travels and no
other data is permitted. In circuit switching, to transfer the data, circuit
must be established so that the data transfer can take place.
• Circuits can be permanent or temporary. Applications which use circuit
switching may have to go through three phases:
• Establish a circuit
• Transfer the data
• Disconnect the circuit
• Circuit switching was designed for voice applications. Telephone is the best
suitable example of circuit switching.
57

58. Circuit Switching
58

59. Message Switching
• This technique was somewhere in middle of circuit
switching and packet switching. In message switching,
the whole message is treated as a data unit and is
switching / transferred in its entirety.
• A switch working on message switching, first receives
the whole message and buffers it until there are
resources available to transfer it to the next hop.
• If the next hop is not having enough resource to
accommodate large size message, the message is stored
and switch waits.
59

60. • Message switching has the following drawbacks:
• Every switch in transit path needs enough storage to
accommodate entire message.
• Because of store-and-forward technique and waits
included until resources are available, message
switching is very slow.
• Message switching was not a solution for streaming
media and real-time applications. 60

61. Packet Transmission Modes
 Broadcast: One sender, all the others as receivers.
 Unicast: One sender and one receiver.
 Multicast: One sender (potentially many senders),
many receivers.
61

62. 62

63. Multicast Applications
ConferenceXP: An Example of Multicast
application
Video Conference
Distance Learning
63

64. Physical media
 bit: propagates between transmitter/receiver pairs
 physical link: what lies between transmitter & receiver
 guided media:
 signals propagate in solid media: copper, fiber, coax
 unguided media:
 signals propagate freely, e.g., radio
1-6464

65. Physical Media
Copper
Coaxial Cable - Thick or Thin
Unshielded Twisted Pair - CAT 3,4,5,5e &6
Optical Fiber
Multimode
Singlemode
Wireless
Short Range
Medium Range
Satellite

66. Satellite Communication

67. 4-Pair Unshielded Twisted
Pair Cable with RJ-45 Connector
RJ-45
Connector
UTP Cord
67

68. Optical Fibers
• Applications:
– Long distance telecommunication
– Greater capacity; 2 Gb/s over 10’s of Km
– Smaller size and lighter weight
– Lower attenuation (reduction in strength of
signal)
– Electromagnetic isolation – not effected by
external electromagnetic environment. Aka
more privacy
– Greater repeater spacing – fewer repeaters,
reduces line regeneration cost
68

69. The modern way to study Networks
• The main issues of networks can be studied by
modeling it in layers. The OSI, And TCP/IP
models are the most known way.
• We will concentrate on the details of the
TCP/IP model layers, as we will see later in
this course.
69

70. 70
Complexity of networks
Networks are complex !!!
 The main Parts of a network:
– Hosts
– Routers
– Media
– Applications
– Hardware
– Software
– Different OS
Is there a Solution?
 Organize all the elements
under a same agreement
 Better yet, use a divide and
conquer approach
 Result: the concept of a
communications protocol
70

71. Example of modeling a process using layer concept
71

72. Computer components as a layers

73. 73
Conceptual Layers of Protocol Software
Sender Receiver
Links of network
The modules of
Protocol SW are
on each machine
stacked vertically
into layers
73

74. 74
Why layering?
 Dealing with complex systems:
– Explicit structure allows identification of complex
system’s pieces
– Modularization eases developing, maintenance, updating
of system
 Change of implementation of layer’s service transparent to rest of
system
74

75. Computer network and Data
Communications
• The main objective of any computer network
is data communication.
• Data communications are the exchange of data
between two devices via some form of
transmission medium such as a wire cable.

76. Five Components of Data
Communication
• Message:
– text, number, images, audio, and video.
• Sender and Receiver
– devices that send/receive data message
– Computer, workstation, telephone, etc.
• Transmission medium
– Physical path through which the message travels
• Protocol
– Set of rules governing data communications

77. Five Components of Data
Communication

78. 1-78
TCP/IP and the Internet
 Doubling in size every year since 1983, 100 million host,
2000 million+ users.
 One thing remained constant:
 Internet is build on the TCP/IP layered model and its protocol.

79. Types of computer network
79

80. 80
Types of Networks
• Networks by components
– P2P (peer to peer) - Client Server-Based
• Networks by Size
– PAN -LAN - MAN - WAN
• Networks by Topology
– Star - Bus - Ring - Hierarchy -Mesh
• Networks by Media
– Guided - Unguided

81. Client/Server Model
• Client –
– device requesting information (initiates the data
exchange)
– Can also UPLOAD data to the servers
• Server – device responding to the request
– How does it handle multiple request from multiple users
and keep everything in order?
–
• Examples:
– E-mail Client on an employee computer issues a request
to the e-mail server for any unread e-mail. The server
responds by sending the e-mail to the client.

82. Peer-to-Peer (P2P) Network Model
• Two or more computers are connected and are able to
share resources without having a dedicated server
• Every end device can function as a client or server on
a ‘per request’ basis
• Resources are decentralized (information can be
located anywhere)
• Difficult to enforce security and policies
• User accounts and access rights have to be set
individually on each peer device

83. How data requests occur
• Client/server model
– Advantages:
– Centralized administration
– Security is easier to enforce
• Peer-to-peer networking and applications

84. Networks by Size

86. Classification of the networks based
Geographical Span
NETWORK
PAN LAN WAN MAN CAN
86

87. PANs (Personal Area Networks)
• PANs (Personal Area Networks) let devices communicate
over the range of a person. A common example is a wireless
network that connects a computer with its peripherals.
• Almost every computer has an attached monitor, keyboard,
mouse, and printer. Without using wireless, this connection
must be done with cables.
• To help these users, some companies got together to design a
short-range wireless network called Bluetooth to connect these
components without wires.
87

88. LAN (Local Area Network)
• The next step up is the LAN (Local Area Network). A
LAN is a privately owned network that operates within
and nearby a single building like a home, office or
factory.
• LANs are widely used to connect personal computers
an consumer electronics to let them share resources
(e.g., printers) and exchange information.
• When LANs are used by companies, they are called
enterprise networks.
88

89. • Wireless LANs are very popular these days. In most
cases, each computer talks to a device, this device,
called an AP (Access Point), wireless router, or base
station, relays packets between the wireless computers
and also between them and the Internet.
• There is a standard for wireless LANs called IEEE
802.11, popularly known as WiFi.
• It runs at speeds anywhere from 11 to hundreds of
Mbps.
89

90. 90

91. CAMPUS AREA NETWORK(CAN)
• The campus area network is made up of an
interconnection of LAN with limited
geographical area.
• Network equipments such as switches, routers
and the transmission media i.e. optical fibre etc
are almost entirely owned by the campus
owner.
91

92. WIDE AREA NETWORK(WAN)
• When network spans over a large distance. A wide area
network(WAN) is installed.
• The communication between different users of WAN is
established using leased telephone lines, satellite links,
mobile towers, or fibre cables.
• It is cheaper and more efficient to use the phone network for
the link.
• Most WAN networks are used to transfer large blocks of
data between its users.
92

93. METROPOLITAN AREA NETWORK(MAN)
• It is in between LAN & WAN technology that
covers the entire city.
• It uses similar technology as LAN.
• It can be a single network such as cable TV
network, or a measure of connecting a number of
LAN’s o a large network so that resources can be
shared LAN to LAN as well as device to device.
93

94. WAN
MAN
CAN
PAN
LAN
94

95. Network topologies
95

96. Network topology
 A topology is a way of “laying out” the
network. Topologies can be either physical
or logical.
 Physical topologies describe how the cables
are run.
 Logical topologies describe how the network
messages travel 96

97. Network topology (cont.)
 Mesh Topology
 To find the number of physical links in a fully connected mesh network
with n nodes, we first consider that each node must be connected to
every other node.
 Node 1 must be connected to n - I nodes, node 2 must be connected to n
– 1 nodes, and finally node n must be connected to n - 1 nodes. We need
n(n - 1) physical links. However, if each physical link allows
communication in both directions (duplex mode), we can divide the
number of links by 2. In other words, we can say that in a mesh
topology, we need
 duplex-mode links.
 For network with 5 nodes, there are 10
 physical links
n(n -1) /2
97

98.  Star Topology
In a star topology, each device has a dedicated point-to-point link
only to a central controller, usually called a hub. The devices are
not directly linked to one another. Unlike a mesh topology, a star
topology does not allow direct traffic between devices.
The controller acts as an exchange: If one device wants to send
data to another, it sends the data to the controller, which then
relays the data to the other connected device .
If one link fails, only that link is affected. All other links remain
active, but If the hub goes down, the whole system is dead. The
star topology is used in local-area networks (LANs),
98

99. Network topology (cont.)
 Ring Topology
In a ring topology, each device has a dedicated point-to-point
connection with only the two devices on either side of it.
A signal is passed along the ring in one direction, from device
to device, until it reaches its destination. Each device in the
ring may incorporates a repeater
99

100. Network topology (cont.)
 Bus topology
The preceding examples all describe point-to-point connections. A
bus topology, on the other hand, is multipoint.
One long cable acts as a backbone to link all the devices in a
network.
A bus technology called Ethernet has become the industry standard
for local-area networks
100

101. Network topology (cont.)
 Advantages and Disadvantages of Network Topologies
101

102. Tree Topology
• also known as Hierarchical Topology, this is the most common form
of network topology in use presently. This topology imitates as
extended Star topology and inherits properties of bus topology.
• This topology divides the network in to multiple levels/layers of
network.
• The lowermost is access-layer where computers are attached. The
middle layer is known as distribution layer, which works as
mediator between upper layer and lower layer.
• The highest layer is known as core layer, and is central point of the
network, i.e. root of the tree from which all nodes fork.
102

103. Tree Topology
103

104. Hybrid Topology
• Hybrid Topology A network can be hybrid. For
example, we can have a main star topology
• with each branch connecting several stations in
a bus topology
104

105. Hybrid Topology
105

106. Question
• Physical or logical arrangement of network is
a) Topology
b) Routing
c) Networking
d) None of the mentioned.
• In this topology there is a central controller or hub
a) Star
b) Mesh
c) Ring
d) Bus
106

107. Question
• Which of the following is/ are the drawbacks of Ring Topology?
A) Failure of one computer, can affect the whole network
B) Adding or removing the computers disturbs the network activity.
C) If the central hub fails, the whole network fails to operate.
D) Both of A and B
• Name of the topology in which there are bidirectional links between each possible
nodes
• A) Ring
• B) Mesh
• C) Star
• D) Tree
107

108. Data transmission
108

109. Data Transmission
• Successful transmission of data depends on:
– The quality of the signal being transmitted
– Characteristics of the transmission medium
• Data rate – bits per second in data
communications
• Noise – Average level of noise over the
communication path.
• Error rate – rate at which errors occur where
error in 1 or 0 bit occurs 109

110. Basic Signal Terminologies
• Bit: binary digit, either 0 or 1
• Bit rate – a method for measuring data
transmission speed – bits per second
• Mbps – millions of bits per second (data
speed; measure of bandwidth = total
information flow over a given time) on a
telecommunication medium
• 8 bits = 1 byte
• Mb – million bits (quantity of data)
• MB – million bytes (quantity of data)
• Gbps – Billion bits per second (data speed)
Kilo K 2^10
Mega M 2^20
Giga G 2^30
Tera T 2^40
Peta P 2^50
Exa E 2^60
Zetta Z 2^70
Yotta Y 2^80
110

111. Importance of bandwidth
Bandwidth is defined as the amount of
information that can flow through a network
connection in a given period of time .
Bandwidth is limited by the laws of physics and by the
technologies used to place information on the media .
111

112. 112
Latency
• Latency, or propagation delay
– The length of time that is required to forward, send, or
otherwise propagate a data frame
– Latency differs depending on the resistance offered by the
transmission medium, the number of nodes
• And in the case of a connectivity device, the amount of
processing that must be done on the packet
• Transmisión time
– The amount of time it takes for a packet to be sent from one
device to another
112

113. 113

114. 114

115. 115
Some kind of network troubles
1- What if the Data gets Corrupted?
Internet
GET windex.htmlGET index.html
Solution: Add a checksum
Problem: Data Corruption
0,9 9 6,7,8 21 4,5 7 1,2,3 6
X

116. 2- What if Network is Overloaded?
Problem: Network Overload
• Short bursts: buffer
• What if buffer overflows?
– Packets dropped
– Sender adjusts rate until load = resources
• Called “congestion control”
Solution: Buffering and Congestion Control
116

117. 3- What if the Data gets Lost?
Internet
GET index.html
Problem: Lost Data
Internet
GET index.html
Solution: Timeout and Retransmit
GET index.html
GET index.html
117

118. Problem: Packet size
Solution: Fragment data across packets
4- What if the Data Doesn’t Fit?
• On Ethernet, max IP packet is 1.5kbytes
• Typical web page is 10kbytes
GETindex.html
GET index.html
118

119. Solution: Add Sequence Numbers
Problem: Out of Order
5- What if the Data is Out of Order?
GETx.htindeml
GET x.htindeml
GET index.html
ml 4 inde 2 x.ht 3 GET 1
119

120. End of part 1