For beginners in Computer Networking field, know about basics about what is Computer Networks, what are ways through which we can communicate, what is meant by protocols, he famous OSI its layers and TCP/IP and its layers, What makes a Networking Device, basic topologies of Computer Networks, special purpose network devices like Switch, routers, repeter, bridges and hub, and basics of networking methods, basics of ethernet, TCP its characteristics, UDP, TCP vs UDP, One would wonder what happens when information particular to each layer is read by the corresponding protocols at target machine or why is it required? 

1. Networking Basics

2. What is a Network?
• Network is a group or system of interconnected people or things.
• Like the human networks that we are all part of, computer networks
let us share information and resources.

3. Understanding Networks
• A Computer Network consists of two or more entities, sharing
information.

5. What makes a Network Device?
• A network device possesses special communications hardware to
make the necessary physical connections to other devices.
• Most modern network devices have communication electronics
integrated onto their circuit boards.

6. Network Protocols
• Assembling the physical pieces of a computer network by itself is
insufficient to make it function – connected devices also require a
method of communication.
• These communication languages are called network protocols.
• TCP/IP the most common protocol found on the internet and in home
networks.

7. How can we connect computer Networks in
organization

8. Mesh
Tree
Bus

9. Networking Basics: Understanding
• Understanding the way a network operates is defined by routing and
switching.
• The network operates by connecting computers and peripherals using
equipments like; switches and routers.
• Switches and routers, enable the devices that are connected to your
network to communicate with each other, as well as with other
networks

10. Device Roles on Computer Network
• Devices on Computer Networks function in different roles. The two
most common roles are Clients and Servers.
• Examples of network Clients include: PCs, phones.
• Client generally make a request and consume data stored in Network
Servers

11. Special Purpose Network Devices
• 1. Network Switches
• 2. Network routers
• 3. Network repeater
• 4. Network Bridge
• 5. Network Hub

12. 1. Network Hub
• A hub is a small, simple, inexpensive electronic device that joins
multiple computers together.
• A hub contains multiple ports.
• When a packet arrives at one port, it is copied to the other ports so
that all segments of the LAN can see all packets.

13. Characteristics of Hubs
• Using Hubs, all computers can communicate directly with each other.
• The number of ports an Ethernet hub supports also varies. Four-and-
Five port Ethernet Hubs are most common in home/small office
networks.
• Basic types of hubs: 1. Passive 2. Active

14. Active Hubs & Passive Hubs
• Active Hubs amplify the incoming packets.
• Passive Hubs do not amplify the electrical signal of incoming packets
before broadcasting them out to the network.

15. Working with Ethernet Hubs
• To network a group of computers using an Ethernet Hub, first connect
an Ethernet Cable into the hub unit, then connect the other end of
the cable to each computer’s network interface card (NIC).
• To expand a network to accommodate more devices, Ethernet hubs
can also be connected to each other, to switches or to routers.

16. When an Ethernet Hub is needed
• Ethernet hubs operate as Layer 1 devices in the OSI model.
• A hub can be useful for temporarily replacing a broken network
switch or when performance is not a critical factor on the network.

17. 2. Network switch
• Network switch is a small hardware device that centralizes
communications among multiple connected devices within one LAN.
• In networks, a device that filters and forwards packets between LAN
segments.
• Switches operate at the data link layer (layer 2)

18. Switches vs Hubs
• In a hub, a packet is broadcasted to every one of its ports causing lot
of traffic.
• A switch, keeps a record of the MAC addresses of all the devices
connected to it, hence it can send packet to particular port.

19. 3. Network Router
• Router forwards data packets along networks.
• It is connected to at least two networks, commonly two LANs and
its ISP network, so router acts at Network layer.
• They are located at gateways, the places where two or more networks
connect.
• It uses forwarding tables to determine the best path for forwarding
the packets.
• They use protocols such as ICMP to communicate with each other.

20. 4. Network Repeaters
• Network Repeaters regenerate incoming electrical, wireless or optical
signals.
• Repeaters attempt to preserve signal integrity and extend the
distance over which data can safely travel.

21. 5. Network Bridge
• A network bridge helps to join two otherwise separate computer
networks together to enable communication between them.
• Ex: Bridge devices are used with LANs for extending their reach to
cover larger physical areas.
• They operate in DLL (Layer 2) of the OSI model.

22. Network Adapters
• Also known as Network Cards, Network Interface Cards, NICs.
• A Network Card’s job is to physically attach a computer to a network,
so that the computer can participate in network communications.

23. Networking Methods
• The two networking methods for transferring data between two
nodes or hosts are.
1. Packet Switching
2. Circuit Switching

24. Packet Switching
• In this network data is transferred by dividing the data into packets
and passing it.
• The route is not exclusively setup, several routing algorithms are used
to route the packets.
• Ex: When we connect PC to website data is transferred in the form of
packets.

25. Circuit Switching
• In this network a static route is setup and pre-established prior to
initializing connections to the host.
• Ex: When landline phones were used, the telco provider would create
a dedicated circuit for that session.

26. Local Area Network
• LAN is a computer network that interconnects computers within a
limited area such as residence, school, laboratory, university campus
or office building.
• Ethernet and Wi-Fi are two most common transmission technologies
in use for local area networks. Few like Token ring, ARCNET where
also used.

27. What is Ethernet in Computer Networking?
• Ethernet is the most common type of connection computers use in a
local area network (LAN). This port can be used to connect your
computer to another computer, a local network, or an external DSL or
cable modem.
• The run length of individual Ethernet cables is limited, but Ethernet
networks can be easily extended using network bridge devices.

28. What is an Ethernet Port?
• An Ethernet port is an opening on computer network equipment
that Ethernet cables plug into.
• An Ethernet port looks much like a regular phone jack, but it is slightly
wider

29. Ethernet Ports on Computers
• Most computers include one built-in Ethernet port for connecting the
device to a wired network.
• A computer's Ethernet port is connected to its internal
Ethernet network adapter.

30. OSI(Open Systems Interconnection) Model
• The OSI model is a reference model for how messages should be
transmitted between any two points in a telecommunications
network. It conceptually divides computer network architecture into
7 layers.
• The lower layers deal with electrical signals, chunks of binary data,
and routing of these data across networks.
• Higher levels cover network requests and responses, representation
of data, and network protocols as seen from a user's point of view.

31. • The 7 layers of OSI Model are:
1. Physical layer
2. Data Link layer
3. Network layer
4. Transport layer
5. Session layer
6. Presentation layer
7. Application layer
Shortcut: Please Do Not Touch Sachin’s Patni Anjali.

32. 1. Physical Layer
• This layer is responsible for transmission of bits from one computer to
another. Functions of Physical Layer:
1. Representation of Bits
2. Data Rate
3. Topologies
4. Transmission Modes
5. Synchronization
6. Line Configuration
7. Interface

34. 2. Data Link Layer
• Functions of DLL: Flow Control, Error Control, Framing, Physical
addressing, Access Control.
• It is further divided into
1. Media Access Control sublayer and
2. Logical Link Control sublayer.

36. 3. Network Layer
• Functions: Logical Addressing, Host-to-Host Connectivity, Switching,
routing.
• If the data has reached the final destination, this Layer 3 formats the
data into packets delivered up to the Transport layer. Otherwise, the
Network layer updates the destination address and pushes the frame
back down to the lower layers.

38. 4. Transport Layer
• The Transport Layer delivers data across network i.e. end-to-end
connections.
• Functionalities: Flow control, Error Control, Segmentation.
• It provides services such as connection-oriented data
stream support, reliability, flow control, and multiplexing.

40. 5. Session Layer
• The Session Layer manages the sequence and flow of events that
initiate and tear down network connections.
• At Layer 5, it is built to support multiple types of connections that can
be created dynamically and run over individual networks.

41. 6. Presentation Layer
• The Presentation layer handles syntax processing of message data
such as format conversions and encryption / decryption needed to
support the Application layer above it.

42. 7. Application layer
• The application layer supplies network services to end-user
applications.
• Network services are typically protocols that work with user's data.
For example, in a Web browser application, the Application layer
protocol HTTP packages the data needed to send and receive Web
page content.
• This Layer 7 provides data to (and obtains data from) the Presentation
layer.

43. TCP/IP Protocol Suite
• Communications between computers on a network is done through
protocol suits. Most widely used protocol suite is TCP/IP.
• A protocol suit consists of a layered architecture where each layer
depicts some functionality which can be carried out by a protocol.

44. The 4 layers of TCP/IP are as follows :
• Application Layer
• Transport Layer
• Internet Layer
• Network Interface Layer.

45. Application Layer
• This layer includes applications or processes that use transport layer
protocols to deliver the data to destination computers.
• Some of the popular application layer protocols are :
HTTP (Hypertext transfer protocol)
FTP (File transfer protocol)
SMTP (Simple mail transfer protocol) etc

46. Transport Layer
• This layer provides backbone to data flow between two hosts. This
layer receives data from the application layer above it.
• There are many protocols that work at this layer but the two most
commonly used protocols at transport layer are TCP and UDP.
• TCP is used where a reliable connection is required while UDP is used
in case of unreliable connections

47. TCP
• TCP divides the data(coming from the application layer) into proper
sized chunks and then passes these chunks onto the network.
• It acknowledges received packets, waits for the acknowledgments of
the packets it sent and sets timeout to resend the packets if
acknowledgements are not received in time.

48. UDP
• UDP provides unreliable service by sending packets from one host to
another.
• For example while streaming a video, loss of few bytes of information
due to some reason is acceptable as this does not harm the user
experience much.

49. Internet Layer
• The main purpose of this layer is to organize or handle the movement
of data on network. By movement of data, we generally mean routing
of data over the network.
• The main protocol used at this layer is IP.

50. Network Interface layer
• This layer is defined by what type of physical network your computer
is connected to.
• Almost always your computer will be connected to an Ethernet
network.
• Ethernet has two main layers
1. Logical Link Control
2. Medium Access Control

52. • The LLC is in charge of adding information of which protocol on the
internet layer delivered to be transmitted, so when receiving a frame
from the network this layer on the receiving computer has to know to
which protocol from the internet layer it should deliver data.
• This layer is in charge of adding the source MAC address and the
target MAC address
• Frames that are targeted to another network will use the router MAC
address as the target address.

53. • The LLC and MAC layers add their own headers to the datagram they
receive from the Internet layer. The complete structure of the frames
generated is shown below

54. TCP/IP Concept Example
• Client requests for a service while the server processes the request
for client.
• Consider the data flow when you open a website.

56. • At Application layer, since HTTP protocol is being used, so an HTTP
request is formed and sent to the transport layer
• TCP protocol assigns some more information to the packet from
upper layer(like sequence number, source port number, destination
port number) so that the communication remains reliable
• At IP layer, it adds IP address.

57. • The data link layer makes sure that the data transfer to/from the
physical media is done properly.
• This information travels on the physical media (like Ethernet) and
reaches the target machine.

58. • Now, at the target machine (which in our case is the machine at which
the website is hosted) the same series of interactions happen, but in
reverse order.
• The packet is first received at the data link layer. The information (that
was stuffed by the data link layer protocol of the host machine) is
read and rest of the data is passed to the upper layer.

59. • Similarly at the Network layer, the information set by the Network
layer protocol of host machine is read and rest of the information is
passed on the next upper layer.
• Same happens at the transport layer and finally the HTTP request
sent by the host application(your browser) is received by the target
application(Website server).

60. One would wonder what happens when
information particular to each layer is read by the
corresponding protocols at target machine or why
is it required?• Well, lets understand this by an example of TCP protocol present at
transport layer.
• At the host machine this protocol adds information like sequence number
to each packet sent by this layer.
• At the target machine, when packet reaches at this layer, the TCP at this
layer makes note of the sequence number of the packet and sends an
acknowledgement (which is received seq number + 1).
• Now, if the host TCP does not receive the acknowledgement within some
specified time, it re sends the same packet. So this way TCP makes sure
that no packet gets lost. So we see that protocol at every layer reads the
information set by its counterpart to achieve the functionality of the layer
it represents.

61. Additional Resources: Port Numbers
• While most standard servers run on standard port numbers, clients do not
require any standard port to run on.
• Standard port numbers are generally chosen from 1 to 1023 and are
managed by Internet Assigned Numbers Authority(IANA).
• Client port numbers are known as ephemeral ports. By ephemeral we
mean short lived.
• This is because a client may connect to server, do its work and then
disconnect.
• Also, since clients need to know the port numbers of the servers to connect
to them, so most standard servers run on standard port numbers

62. Purpose of Network Protocols
• Network protocols serve these basic functions:
1. Address data to the correct recipient.
2. Physically transmit data.
3. Receive messages and send responses appropriately.
• Network protocols have similar comparison with postal service. Just
as the postal service manages letters from many sources and
destinations, so too do network protocols keep data flowing along
many paths continuously.

63. How computer Networks work
• Any functional computer network requires devices to be physically
connected in some fashion. Connections may be wired via cables or
wireless via compatible signaling hardware on each device
• Types of Network Interconnects
• Wired interconnects include:
1. Ethernet - Networking technology that joins local devices together
via Ethernet cables.
2. Fiber optic cables transmit digital data using pulses of light.
3. Copper lines

64. • Wireless interconnects include:
1. Wi-Fi is synonymous with wireless networking.

65. Types of Network Communication
• Simplex vs. duplex. With simplex connection only one device can
send data at a time. Conversely, duplex network connections both
devices can share data at a time.
• Connection-oriented or connection-less. A connection-oriented
network protocol exchanges (a process called a handshake) address
information between two devices that allows them to carry on a
conversation (called a session) with each other.

66. What is Ethernet Cable?
• An Ethernet cable is network cable used on wired networks. Ethernet
cables connect devices on LAN such as PCs, routers and switches.
• Types of Ethernet cables 1. Category 5 (CAT 5) 2. Category 6 (CAT6)

68. Limitations of Ethernet Cables
• A single Ethernet cable, like an electric power cord, can extend only
limited distances due to their electrical transmission characteristics.

69. Alternatives to Ethernet Cables for computer
Networking
• Wireless Technologies like Wi-Fi and Bluetooth have replaced
Ethernet on many home and business networks.

70. Network interface controller/card
• NIC is computer hardware component that connects a computer to a
computer network.

71. Host Bus Adapter (HBA)
• A Host Adapter connects a host system to other network and storage
devices.
• The terms are primarily used to refer to devices for connecting
SCSI, Fibre Channel and eSATA devices.

72. Transmission Control
Protocol (TCP)

73. • TCP is a standard that defines how to establish and maintain a
network conversation via which application programs can exchange
data.
• TCP is reliable, connection oriented protocol and offers end-to-end
packet delivery. It acts as back bone for connection.
• TCP works with the IP (IP defines how computers send packets of
data).

74. Features of TCP
• TCP corresponds to Transport Layer of OSI Model.
• It is a connection oriented protocol, which means a connection is
established and maintained until the application programs at each
end have finished exchanging messages.
• It determines how to break application data into packets, sends
packets to & accepts packets from network Layer.
• It manages flow control and because it is meant to provide error-free
data transmission - handles retransmission of dropped or garbled
packets as well as acknowledgement of all packets that arrive

75. Internet Protocol
• IP provides an unreliable packet delivery system– each packet is an
• It ensures no guarantee of successfully transmission of data.
• In order to make it reliable, it must be paired with reliable protocol
such as TCP at the transport layer.

76. • IP by itself is something like postal system. It allows to address a
package and drop it in the system, but there’s no direct link bw you
and the recipient.
• TCP/IP, establishes a connection between two hosts so that they can
send messages back and forth.

77. Understanding TCP/IP
• We know TCP/IP has four layers. Programs talk to the Application
layer. On the Application layer we will find Application protocols such
as SMTP (for e-mail), FTP (for file transfer) and HTTP (for web
browsing).
• Each kind of program talks to a different Application protocol,
depending on the program purpose.
• After processing the program request, the protocol on the Application
layer will talk to another protocol from the Transport layer, usually
TCP. TCP is in charge of getting data sent by the upper layer, dividing
them into packets and sending them to the layer below, Internet.

78. • Also, during data reception, Transport layer is in charge of putting the
packets received from the network in order (because they can be
received out-of-order) and also checking if the contents of the
packets are intact.
• On the Internet layer we have the IP (Internet Protocol), which gets
the packets received from the Transport layer and adds IP address of
source and destination.
• Then, the packets are sent to the Network Interface.

79. • The Network layer will send packets over the network.
• What is inside this layer will depend on the type of network your
computer is using. Nowadays, commonly Ethernet is used.
• We generally find Logic Link Control (LLC), Medium Access Control
inside Ethernet Layer.

80. Practical Scenario
• When a Web server sends an HTML file to a client, it uses the HTTP
protocol to do so.
• The HTTP program layer asks the TCP layer to set up the connection and
send the file.
• The TCP stack divides the file into packets, numbers them and then
forwards them individually to the IP layer for delivery.
• Although each packet in the transmission will have the same source and
destination IP addresses, packets may be sent along multiple routes.
• The TCP program layer in the client computer waits until all of the packets
have arrived, then acknowledges those it receives and asks for the
retransmission on any it does not (based on missing packet numbers), then
assembles them into a file and delivers the file to the receiving application.

81. • Retransmissions and the need to reorder packets after they arrive can
introduce latency in a TCP stream.
• Highly time-sensitive applications like Voice over IP (VoIP) and
streaming video generally rely on a transport like UDP (not TCP) that
reduces latency and Jitter, by not worrying about reordering or
getting missing data retransmitted.

82. TCP vs IP
• Setting up TCP connection is somewhat like setting up highway for packets to
move.
• But the actual packets are moved by IP.
• At the receiving end, since TCP is reliable, the sequence number which was
assigned by TCP in other end are compared and packets are formatted to have
seamless transfer of data.
• TCP connection is somewhat like a telephone connection; you need to know not
only the phone number (IP address), but because the phone may be shared by
many people at that location, you also need the name or extension of the user
you want to talk to at the other end (port number).
• The analogy can be taken a little further. If you don't hear what the other person
has said, a simple request ("What?") will prompt the other end to resend or
repeat the phrase, and the connection remains open until someone hangs up.

83. Types of LAN Technology

84. 1. Ethernet
• Ethernet is the most popular physical layer LAN technology in use
today. It defines the number of conductors that are required for a
connection, the performance thresholds that can be expected, and
provides the framework for data transmission.
• A standard Ethernet network can transmit data at a rate up to 10
Megabits per second (10 Mbps)

85. 2. Fast Ethernet
• The Fast Ethernet standard (IEEE 802.3u) has been established for
Ethernet networks that need higher transmission speeds.
• This standard raises the Ethernet speed limit from 10 Mbps to 100
Mbps with only minimal changes to the existing cable structure.

86. 3. Gigabit Ethernet
• Gigabit Ethernet was developed to meet the need for faster
communication networks with applications such as multimedia and
Voice over IP (VoIP)

87. 4. Token ring
• Token Ring is another form of network configuration. It differs from
Ethernet in that all messages are transferred in one direction along
the ring at all times.
• Token Ring networks sequentially pass a “token” to each connected
device.
• When the token arrives at a particular computer (or device), the
recipient is allowed to transmit data onto the network. Since only one
device may be transmitting at any given time, no data collisions occur

88. • Access to the network is guaranteed, and time-sensitive applications
can be supported.
• However, these benefits come at a price. Component costs are usually
higher, and the networks themselves are considered to be more
complex and difficult to implement

89. Collisions
• Ethernet is a shared medium, so there are rules for sending packets of
data to avoid conflicts and to protect data integrity.
• It is possible that two or more nodes at different locations will
attempt to send data at the same time because Ethernet allows each
device to send messages at any time without having to wait for
network permission. When this happens, a packet collision occurs.
• This leads to competition for network bandwidth and can slow the
performance of the network from the user’s point of view.
• Segmenting the network is one way of reducing an overcrowded
network, i.e., by dividing it into different pieces logically joined
together with a bridge or switch.

90. CSMA/CD
• Carrier Sense Multiple Access/Collision Detection (CSMA/CD) is a
type of contention protocol that defines how to respond when a
collision is detected, or when two devices attempt to transmit
packages simultaneously.
• After detecting a collision, each device that was transmitting a packet
delays a random amount of time before re-transmitting the packet. If
another collision occurs, the device waits twice as long before trying
to re-transmit.

91. • The IEEE Standard 802.3. This standard defines rules for configuring
an Ethernet network and also specifies how the elements in an
Ethernet network interact with one another.
• Ethernet is popular because it strikes a good balance between speed,
cost and ease of installation, the ability to support virtually all popular
network protocols, make Ethernet an ideal networking technology for
most computer users today.