1. NETWORKING
COMMUNICATION
Exchanging message among several parties is known as COMMUNICATION.
DATA COMMUNICATION
COMPONENTS OF COMMUNICATION.
Typically data communication consists of three components.
1. Sender or source of data
2. Receiver
3. Medium
MODE OF DATA COMMUNICATION
According to transmission of data it can be derived as,
SIMPLEX DATA COMMUNICATION.
In which mode direction of flow of data is always in one direction, it means a terminal always
act as sender and the other one as receiver.
Eg: radio, TV
DUPLEX DATA COMMUNICATION.
In which mode direction of flow of data is in both directions, it can be further divided as,
1. Half duplex
2. Full duplex.
1. Half duplex.
Data flow does not take place in both directions at simultaneous time.
Eg: walkie-talkie
2. Full duplex.
In which mode of flow of data take place in both directions at simultaneous time.
Eg: telephone, mobile
MODE OF COMMUNICATION
Simplex Duplex
S R S R

2. TRANSMITTER &RECEIVER
TRANSMITTER
In telecommunication, transmitter is an electronic device which produces radio waves and
through these waves data is transmitted.
Transmitter and receiver combined in one unit is called TRANSCEIVER.
The information is provided to the transmitter in the form of an electronic signal.
RECEIVER
Is an electronic device that receives information (data) carried by the network.
COMMUNICATION MEDIUM.
The path through which the data communication takes place. (Channel or medium)
DATA COMMUNICATION.
Communication of binary encoded data from one place to another.
Transmission media is what actually carries signals from one point to another. This may include
copper wiring in the case of twisted pair cable or coaxial cable or electronic waves in the case of
micro waves or satellite transmission.
Communication media can be classified as; 01.Guided or Bounded or Wired media
02. Unguided or Unbounded or Wireless media.
01.Guided media.
Confine the data to specific physical pathways.
Eg: wire, optical fibers
1. Twisted Pair (TP).
Two wires twisted around one another, two insulated copper wire in a regular spiral
pattern as a single communication link. Used in- LAN network, PC to PC network.

3. 2. Coaxial Cable.
Two conductors share a common axis, outer conductor act as shield, signal is transmitted on
the inner core. The inner core and the outer core are separated by an insulator.
Used in- TV antenna, cable TV
4. Fiber Optics.
Fiber optic cables utilize light waves to transmit data through a thin glass or plastic fiber
which consists of hundreds of thin glass or plastic wires that transmit pulsation beams of
light.
Advantages of using fiber optics.
 Long distance
 With high rate
 Without data loss
 Through interference of magnetic flux.
02.Unguided media
The media allows the data transmission without physical wiring. WAN make use of
wireless technology. Radio transmission and infrared (IR ) are popular technology.
Eg: radio transmission
Infrared transmission
Microwave transmission
Satellite transmission
Wi-Fi
Bluetooth
PROTOCOLS
Is a system of digital rules for data exchange within or between networks.
A protocol can therefore be implemented as hardware, software, or both. Communications
protocols have to be agreed upon by the parties involved.

4. SYNCHRONIZATION AND ACKNOWLEDGEMENT
SYNCHRONIZATION
Synchronization also occurs between network nodes to ensure that data streams are received
and transmitted correctly to prevent data collision. It usually uses a clock signal, transmitted in
sequence with a data stream to maintain proper signal timing.
ACKNOWLEDGEMENT
Is a signal passed between communicating processes or computers to signify acknowledgement
or receipt of response as a part of communication protocol. The acknowledgement function is
used in the Automatic Repeat Request (ARQ) function. Acknowledgement frames are
numbered in co-ordination with the frames that have been received and then sent to the
transmitter. This allows the transmitter to remain within the window size of the receivers
buffers and to become aware about some missed frames.
SIGNALS
A signal is an electrical or electromagnetic current that is used for carrying data from one
device or network to another.
It is the key component behind virtually all; communication
Networking
Computing
Electronic device
SIGNAL CLASSIFICATION
Signal can be classified as, 01.Digital signal
02. Analog signal.
01. Digital Signal.
A digital signal is a physical signal that is a representation of a sequence of discrete
values.

5. 02. Analog signal
Is any continues signal for which the time varying feature (variable) of the signal is a
representation of some other time varying quantity.
Eg: voice, sound
REPRESENTATION OF DATA IN SIGNAL FORM
Signal is the transmission of data. Both data and signal can be either analog or digital form.
There are four combinations transmitted data using signal.
Digital data Analog signal
Digital signal Transmitting digital data using
digital signal.
Transmitting analog data
using digital signal.
Analog signal Transmitting digital data using
analog signal.
Transmitting analog data
using analog signal.
DATA AND SIGNAL
Data are entities that convey meaning within a computer or computer system. If you want to
transfer this data from one point to another, either by using a physical wire or by using radio
waves, the data has to be converted into a signal. Signals are the electric or electromagnetic
encoding of data and are used to transmit data.
CONVERTING DATA INTO SIGNALS
Normally, digital signals convey digital data and analog signal convey analog data. However,
opposite action also can be done. The choice of using either analog or digital signals often
depends on the transmission equipment that is used and the environment in which the signals
must travel.

6. MANUAL METHODS
MANUAL COMMUNICATION METHODS
The manual communication system use articulation of hands, signals, gestures to mediate
message between persons. They are received visually and some time factually. When it is a
primary form of communication may be enhanced by body language and facial expression.
ELECTRONIC AND COMPUTER BASED OF COMMUNICATION
Any form of communication between two or more individual people who interact and or
influence each other via computers or electronic media.
 Telephone
 Radio or television
 Satellite
 ISDN
 ADSL or DSL
 CDMA
 GPRS
 GSM
 3G or 4G
 HSDPA or W-CDMA
Telephone
A telephone or phone is a telecommunications device that permits two or more users to
conduct a conversation when they are not in the same vicinity of each other to be heard
directly. A telephone converts sound, typically and most efficiently the human voice, into
electronic signal suitable for transmission via cables or other transmission media over long
distances.
Telephone is invented by Alexander Graham-Bell.
Radio and television
Broadcasting, radio and television, primary means by which information and entertainment are
delivered to the public in virtually every nation around the world. The term broadcasting refers
to the airborne transmission of electromagnetic audio signals (radio) or audiovisual signals
(television) that are readily accessible to a wide population via standard receivers.
Satellite
a communication satellite or Camsat is an artificial satellite sent to space for the purpose of
telecommunications, modern communications satellites use a variety of orbits including
geostationary orbits, Molniya orbits, elliptical orbits, elliptical orbits and low (polar and non-
polar) earth orbits. Satellites provide a microwave radio relay technology.

7. ISDN(Integrated Services DigitalNetwork)
Is a set of CCITT/ITU standards for digital transmission over ordinary telephone copper wire as
well as over other media. ISDN in concept is the integration of both analog or voice data
together with digital data over the same network.
ADSL or DSL
ADSL- Asymmetric Digital Subscriber Line
DSL- Digital Subscriber Line
Is a family of technologies that provide internet access by transmitting digital data using a local
telephone network which uses the public switched telephone network.
CDMA (Code Division Multiple Access)
Is an example of multiple accesses, which is where several transmitters can send information
simultaneously over a single communication channel. This allows several users to share a band
of frequencies to permit this without undue interference between the users.
W-CDMA (Wideband Code Division Multiple Access)
UMTS (UniversalMobile Telecommunication System)
HSPDA (High-Speed Downlink PacketAccess)
Is an enhanced 3G mobile telephone communication protocol having higher data speed and
capacity.
GPRS (General Packet Radio Service)
Is a packet oriented mobile data service on the 2G and 3G cellular communication systems
Global System for Mobile communications. (GSM)
Data transmissionandreception
Transmission is the process of sending and propagating an analog or digital information signal
over a physical point-to-point or point-to-multipoint transmission medium either wired optical
fiber or wireless.
Transmitted data via signal in a communication systemshould be received in receiver’s terminal
According to the specific protocol. This process is known as data reception.

8. Carrier signal
Is a transmitted electromagnetic pulse or wave at a steady base frequency of alteration on
which information can be imposed by increasing signal strength. This may be laser generated
light beam.
Transmitted
Basic modulationtechniques
Modulation
Is the process of varying one or more properties of a periodic wave (carrier signal) with
modulating signal that contains information to be transmitted.
Modulation of a sine wave form transforms a base band message signal into a pass band signal.
Analog modulation
Modulator is the device that performs modulation. The inverse of modulation is
demodulation.
The device that performs demodulation is demodulator.
MODEM (Modulator-Demodulator) can perform both operations.
Digital modulation
Transferring a digital bit stream over an analog band pass channel.
Eg: PSTN (Public Switched Telephone Network)
Analog modulation techniques.
AM (Amplitude Modulation)
FM (Frequency Modulation)
PM (Phase Modulation)
AM (Amplitude Modulation)
Amplitude of the carrier signal is varied in accordance to the instantaneous amplitude of the
modulating signal.
There are three basic ways to modulate a sine wave radio carrier modifying the amplitude,
frequency and phase.
carrier
Signal

9. ASK (Amplitude Shift Keying)
Is a form of amplitude modulation that represents digital data as variations in the amplitude of
carrier wave.
FSK (Frequency ShiftKeying)
Is a frequency modulation scheme in which digital information is transmitted through discrete
frequency changes of a carrier wave. The simplest FSK is binary FSK. (B-FSK)

10. PSK (PhaseShift Keying)
Is a digital modulation scheme that conveys data by changing phase of reference signal.
ANALOG TO DIGITAL CONVERSATION
An analog to digital converter is a device that converts a continuous physical quantity (voltage)
to a digital number that converts amplitude of quantity.

11. DIGITAL TO ANALOG CONVERSION
Is a function that converts digital data (binary) into an analog signal (electric current or voltage
or electric charge).
MODEM (Modulator-Demodulator)
Is a device that modulates signals to encode digital information and demodulates signals to
decode the transmitted information.

12. Multiplexing
Is a technique by which different analog and digital streams of transmissions can be
simultaneously processed over a shared link.
It divides the high capacity medium into low capacity logical medium to be shared by different
stream; through guided or unguided media multiplexing is possible.
A device that performs multiplexing is called Multiplexer (Mux) and a device that performs the
reverse process is Demultiplexer (Demux).
Application areas:
 Telegraphy
 Telephony
 Video processing
 Digital broadcasting
 Analog broadcasting.
More than one sender tries to send over a single medium multiplexer divides the physical
channel and allocates one to each. On the other end of communication a Demultiplexer
receives the data from a single medium and identifies each and send to different receivers.

13. Types of Multiplexing
Frequency Division Multiplexing (FDM)
Time Division Multiplexing (TDM)
Code Division Multiplexing (CDM)
Frequency Division Multiplexing (FDM)
Is an analog technology.
Divides the spectrum or carrier bandwidth in logical channels and allocate one user to each
channel.
Each user can use the channel independently without overlapping each to other.
Channels are separated by guard bands (guard bands- is a frequency which is not used by any
channel).
Time Division Multiplexing (TDM)
Commonly used in digital signal, but can be used in analog too.
Shared channel is divided among it’s used by means of time slot. Each user can transmit data
within the provided time slot only.
Digital signals are divided in frames equivalent to time slot. (Frame of an optimum size which
can be transmitted in given time slot).
A TDM works in synchronized mode (Multiplexer and Demultiplexer are timely synchronized)
Code Division Multiplexing (CDM)
Multiple data signal can be transmitted over a single frequency in this method.
Allows its user to full bandwidth and transmit signals all the time using a unique code
(orthogonal code).
Signals travels with these unique code (chips) independently.
Receiver should know the code.

14. TRANSMISSION IMPAIRMENTS
In any communication system it must be recognized that the received signal will differ from the
transmitted signal. This is known as Transmission impairments.
Due to transmission impairments random modifications in the received signal that degrade the
signal quality.
O1. Attenuation.
Loss of energy, the strength of a signal falls off with distance over any transmission
medium. This can be expressed as constant number of decibels per unit distance in guided
media.
02. Distortion.
Various frequency components of a signal will arrive at the receiver at different times.
The distortion is caused by the fact that the velocity of propagation of a signal through a
guided medium varies with frequency. For a band limited signal, the velocity tends to be
highest near the center frequency and lower toward the two edges of the band.
Impairment causes
Attenuation Distortion Noise

15. 03. Noise.
In data transmission event additional unwanted signals that are inserted somewhere
between transmission and reception. The latter, undesired signals are referred to as noise.

16. Noise can be divided into four categories:
 Thermal noise
 Intermediation noise
 Crosstalk
 Impulse noise
Thermal noise
Is due to thermal agitation (heat) of electrons in a conductor. It is present in all electronic
devices and transmission media and is a function of temperature.
Intermediation noise
Is produced when there is some non linearity in the transmitter, receiver or intervening
transmission system.
Cross talk
Has been experienced by anyone who, while using the telephone has been able to hear another
conversation, it is an unwanted coupling between signal paths.
Impulsenoise
Voice transmission may be corrupted by short clicks and crackles with no loss of intelligibility.
Computer network
Is a network the allows computer to exchange data.
In computer network devices pass data to each other along data connections.
Data is transferred in the form of packets.
The connections between nodes are established using either cable media or wireless media.
Network nodes
A network computer device that originates, routes, and terminates the data.
Host networking hardware.
Devices are said to be networked together when one device is able to exchange information
with the other device, whether or not they have a direct connection to each other.
Internet is best known computer network. (Network of networks)

17. Advantages of computer network
1. File sharing
it allows remote file access.
Anyone on that network can access a file or update it.
Clients share the storage capacity.
2. Resource sharing
all the computers can be interconnected using a network, and just one modem and
printer can efficiently provide the services to all.
3. Inexpensive set-up
Saves the expense of buying and installing the same software (hardware) as many times
for as many users.
4. Flexible handling
a user can log on to a computer anywhere on the network and access his files.
5. Increasedstorage capacity
Disadvantages of computer network
1. Security concerns
a hacker can get unauthorized access by using different tools.
2. Virus and malware
Viruses can spread on network easily, because of the inter-connectivity of workstations.
3. Lack of robustness
if the main file server of a computer network breaks down, the entire system becomes
useless.
4. Needs efficiency
5. Lack of independence.

18. NETWORK TYPES
PAN (PersonalArea Network)
Smallest network
Restricted to a user
Connectivity range up to 10meters
Technologies- Bluetooth
Infra-red (IR)
Wi-Fi
PC-PC (Peer-Peer)
Hotspot
Tethering
It may include wireless keyboard, mouse, printers, TV remotes and headphones.
LAN (Local Area Network)
This type of network is spanned inside a building and operated under single administrative
system.
It covers an organization, school.
It enables sharing of resources among end-users.
Consists of inexpensive networking and routing equipment.
Mostly operates on private IP address.
Controlled centrally.
Ethernet or Token-ring technology is used.
Wired or wireless or both.

19. MAN (Metropolitan Area Network )
Larger than LAN and smaller than WAN. Normally expands throughout a city. (Cable TV
network).
Used to connect all branches of an organization in the city.
It may use high capacity and high speed fiber optics. This provides uplink for LANs to WANs
internet.
WAN (Wide Area Network)
It spans beyond the geographical region. Across a province or country.
Equipped with very high speed back-bone and very expensive network equipment.
DAN (Desk Area Network)
Is an interconnection of computer device around the ATM (Asynchronous Transfer Mode)
Exchanging of information between various peripherals and CPU.

20. CAN (Controller Area Network)
It allows the micro controllers and devices to communicate with each other without a host
computer.
COMPUTER NETWORK TOPOLOGIES
The way of (the physical layout) connection of the devices physically in a network.
Sometimes, logical topology also considered.
 Bus topology
 Star topology
 Ring topology
 Mesh topology
 Tree topology
 Hybrid topology

21. COMPUTER NETWORKMODELS
1. Peer topeer model
is an approach to computer networking where all computers share equivalent resource
sharing for processing data. (peer networking)
Characteristics of peer to peer
common on small Local Area Networks (LANs), particularly home networks (wired or
wireless) can be configured as peer to peer environment.
Using same networking protocols.
Using peer to peer network sharing of files, printers and other resources easily shared
among workgroup.
2. Client-server model
Is a network computing model that partisan’s task or workloads between the providers
of a resource or service (server), and service requesters (client).
Server and Client communicate over a computer network on separate hardware. But
may reside in the same system.
a server host runs one or more server programs which share their resources with
clients.
A client does not share any of its resources. But, requests a server’s content or service
function.
Clients therefore initiate communication sessions with servers which await incoming
requests.
eg: web server- providing web pages.
Client-server configuration
in the client server architecture, a server provided with service and resources
(applications and hardware).
Those services and resources can be accessed from many clients.
Web servers
The function is to store, process and deliver WebPages to clients.
The communication between Client and Server takes place HTTP (Hyper Text Transfer Protocol).
Pages delivered as mostly HTML, which may include text, images, video, audio, style sheets and
scripts.
Client makes a request (by initiating a communication using HTTP) through a web browser.
Server provides a service if it is available. Else, error message is displayed.
Popular server sight scripting are, ASP, PHP.

22. Mail server
An email server is a computer within the network works as virtual host office.
Consists of a storage area where email is stored for the user.
It maintains a database about its user.
The person who is responsible for maintaining mail server referred to as post master.
eg: SMTP
POP/IMAP
Proxy servers
Is a server that acts as an inter-mediatory for request from clients seeking resources from other
servers.
Web proxies, facilitating access to content on the World Wide Web (WWW) and providing
anonymity.
Uses of Proxy Servers
monitoring and filtering
Content-control software
filtering of encrypted data
Bypassing filters and censorship
Logging and eavesdropping
Improving performance
Translation
Accessing services anonymously
Security
Applicationservers
This is known as App server.
Is a program that handles all applications operations between users and back-end business or
database.
Used for complex based transmission application.
DNS (Domain Name System)
DNS server is any computer registered to join domain name system. A DNS server runs special
purpose networking software.
it features a public IP address and contains a database of network name and address for
internet hosts.
DHCP (Dynamic HostConfiguration Protocol)
DHCP server manages a pool of IP addresses and information about client configuration
parameter such as domain name, name servers, time servers and default gateway.

23. Leasedlines
Is a service contact between a provider and customer.
Provider agrees to deliver a symmetric telecommunication for monthly rent or term sometimes
this is known as “private circuit”or “data link”.
Does not have a telephone number.
Terminals are permanently connected.
Used for TP, data or internet services.
ISP (InternetServiceProvider)
Is an organization that provides services for accessing and using the internet.
Typical services provided by ISP,
Internet access
Internet transit
Domain name registration
Web hosting.
Types of ISP
Access providers- providing connection. Eg: telecom
Edge providers- creating internet content.
Mailbox providers- providing hosting electronic mail domains which access to storage
for mail boxes. Eg: Gmail, ymail
Hosting ISP- providing email, web hosting and online storage.
Transit ISP
Virtual ISP
Free ISP
Wireless ISP
DEVICES USED IN NETWORK
Modem
NIC
Network cables
Repeaters and Regenerators
Hubs, Bridges and Switches
Routers and Gateways
MODEM
Is a device that modulates (modify) signals to encode digital information and demodulate
signals to decode the transmitted information.
Data transfer of a MODEM measure- bps (bits per second)
NIC (Network InterfaceCard)
Is an interface that connects a computer to a network.
Using Ethernet technology.

24. Network Cable
Repeaters andRegenerators
Repeater is an electronic device that receives a signal and transmits it at a high level or power
or on to the other side of an obstruction.
Signal that can cover long distance.
Regenerator is used to determine when the output signal switches its state. (Recovering the
clock timing information)
Hub
Is a small box, power is supplied externally used in a network (star or hierarchical topology) to
share or connect different computers.
Once hub gets a data without considering the destination address, it forward the data to all
devices connected in the network (in the hub).
The relevant node picks it up, others discarded.
Switches
Switches are most intelligent than Hub.
They forward the data to original destination only.
Bridges
Is a device that connects a LAN that uses the same protocol.
Gateways and Routers
Gateways and Routers are used to regulate network traffics between two or more separate
networks.
Gateways regulates traffic between two dissimilar networks, while Routers regulate traffic
between similar networks.
Protocols
A systemof digital rules for data exchange within or between computers. (Network)
It can be implemented as hardware or software or both.
A communication protocol have to be agreed by the parties involve to reach agreement should
be developed into a standard.

25. BASIC REQUIREMENTS OF A PROTOCOL
In a communicating systemto establish a communication messages must be sent and received.
The following factors should be addressed in the protocol
01. Bit strings
Data packets consists of two parts; Header and Data Area.
Data area consists of actual message and header area consists of protocol
information.
If the Bit string longer than transmission unit (MTU-Maximum Transmission Unit)
divided piece of appropriate size.
02. Address unit
Sender and receiver are identified by receiver which is stored under header area of
bit string.
The rules describing meaning of address value are collectively known as addressing
scheme.
03. Address mapping
protocols need to map address from one scheme to another.
04. Routing
if the systems are not directly connected an inter-mediatory systemroutes the
intended receivers on the internet is known as internetworking.
05. Detection of transmission error
it is very important on networks which cannot guarantee error free operation.
06. Acknowledgement
07. Loss of information
Some basic protocols usedinnetworking
Ethernet , IEEE 802.3 (CSMA/CD)
Token ring- IEEE 802.5
IP , TCP , UDP , ICMP
FTP , SMTP , POP , PPP , Telnet
Ethernet
IEEE (Institute of Electronic Electrical Engineering)
Is a family of computer networking technology.
Used in – LAN, MAN, WAN
commercially introduced in 1980 and standardized in 1983 as IEEE 802.3.
It supports higher bit-rates and longer link distance.
Replaced by competing wired LAN technologies as Token Ring, FDDI and ARCNET.
Wireless LAN standardized IEEE 802.11 is known as Wi-Fi.

26. Token Ring
LAN technology resides at the Data Link Layer (DLL) of the OSI model.
Uses a special three-byte frame called a token that travels around the ring.
Initially used in IBM computers and eventually standardized with protocol IEEE 802.5
The process of Token ring
Empty information frames are continuously circulated on the ring.
When the computer has message, seize the frame and assign the message.
Frame is examined by each successive work station.
Workstation copies the data and destination from the frame and changes the token status as
zero.
IP (Internet Protocol)
Principal communication protocol in the internet protocol suite for relaying datagram across
network boundaries.
Delivers the packets from source host to destination host based on the IP address in the packet
headers.
IP defines packet structures that encapsulate the data to be delivered and defines addressing
methods that are used to label the diagram with source and destination.
Introduced by Vint Cerf and Bob Kahn. Versions are, IPV4 and IPV6.
TCP (Transmission ControlProtocol)
Mostly used in major internet applications such as WWW, email, remote administration and file
transfer.
Is a core protocol of internet suite.
Complemented the IP protocol. Therefore the entire suite referred to as TCP/IP.
TCP provides reliable, ordered and error-checked delivery of a stream of octets between
applications running on hosts communicating over an IP networks.
UDP (User Datagram Protocol)
Core member of IP suite.
Designed by David P.Reed in 1980.
Formally defined in RFC 768.
Uses simple connectionless transmission model with a minimum of protocol mechanism.
Has no handshaking dialogue.
No guarantees of delivery, ordering, duplicate protecting.
Provides checksums for data integrity to p[ort numbers to functions of the source and
destination of the datagram.
It is suitable for error checking and correction are either not necessary or is performed the
application.
Time sensitive applications often use UDP.
Because dropping packets is preferable to waiting for delayed packets. But not be an option in a
real time system.

27. Handshaking
Is an automated process of negotiation that dynamically sets parameters of a communications
channel established between two entities before normal communication over the channel
begins.
Checksums or Hash sum
Is a small size datum from a block of digital data (calculated by a function) for the purpose of
detecting errors which may have introduced during the transmission or storage.
Check put
The actual procedure which produces the checksum for a given data input.
Datagram
Is a basic transfer unit associated with a packet switched network.
The delivery, arrival time and order of arrival are not to be guaranteed.
According to RFC 1594,
A self contained independent entity of data carrying sufficient information to be routed from
the source to the destination computer without reliance on earlier exchange between this
source and destination computer and the transporting network.
ICMP (Internet ControlMessageProtocol)
One of the main protocols of the internet protocol suite.
Used by network devices (router)to send error message indication.
Eg: - “requested service is not available”
“Host or router could not be reached”
Can be used to relay query messages.
Not typically used to exchange data between systems.
ICMP for IPV4 and IPV6 is for ICMPV6.
FTP (File Transfer Protocol)
A standard network protocol is used to transfer computer files from one host to another host
over a TCP based network. (Internet)
Built on client server architecture.
Uses separate control and data connection between client and server.
It is secured with SSL/TLS (FTPs)
FTP has been incorporated web page editors.

28. SMTP (Simple Mail Transfer Protocol)
An internet standard for e-mail transmission by default uses TCP port 25.
Protocol for mail submission is same but uses port 587.
Secured by SSL (SMTPs port no.465)
Mail servers and transfer agents used to send and receive mail message. But client level mail
application SMTP for sending message and POP3 or IMAP for receiving message.
POP (PostOffice Protocol)
Application layer internet standard protocol used by local email clients to retrieve email from a
remote server over a TCP/IP connection.
Current standard version is POP3.
PPP (Point to Point Protocol)
Data link protocol used to establish a direct connection between two nodes. It can provide
connection authentication, transmission encryption (using ECP, RFC 1968) and compression.
Used in serial cable, cable, phone line, trunk line, cellular telephone, specialised radio links and
fiber optic links such as SONET.
ISP uses PPP for customers for dial-up access to the internet.
Derivaties of PPP are,
PPPoE, PPPoA are used to subscribe DSL internet service connection to customers by ISP.
Used as a data link layer protocol for connection for synchronous and asynchronous circuits.
Telnet
Is an application protocol used on the interent or LAN to provide a bi-dierctionsal interactive
text oriented communication facilty using a virtual terminal connection.
Developed in 1968. Beginning with RFC 15 and extended in RFC 854.
Standerdised as Internet Engineering Task Force (IETF) Interent Standard STD8.

29. Layered Architecture
Most network are organised as a series of layers or levels to reduce therir design complexity.
Number of layers, name , content, functions differ from network to network.
Designissues for layers
 Mechanism for identifying senders and receivers
 Rules for data transfer
 Error control
 Possible loss of sequencing
 Transmission rate
 Length of messages
 Multiplexing
 Route
(Route- when there are multiple paths between source and destination a Route must be
chosen.)
Interfaces andservices.
Service is a set of primitive (basic) operations that a layer provides to the layer above it.
A service to an interface between two layers with the lower layer being the service provider
and the upper layer being the user.
Types of services
1. Connectionorientedservices
2. Connectionlessservices
1.Connectionorientedservices
Service user first establish the connection.
Uses the connection and then releases the connection.

30. Six different types of services
 In networks, OSI reference model, TCP/IP reference model are the most important
network architectures.
OSI reference model
 Developed by International Standard Organization.
 ISO OSI (Open System Interconnection)

32. Comparisonof TCP/IP layers
The principles that were appliedtoarrive OSI model
 A layer should be created where a different level of abstraction is needed.
 Each layer should perform a well defined function.
 The function of each layer should be chosen with an eye toward defining internationally
standardized protocols.
Three concepts central to OSI
1. Services
2. Interfaces
3. Protocols
1. Services
The service definition tells that,
 What the layer does,
Not
 How entities above it access it
Or
 How the layer works.
2. Interfaces
 A layer’s interface tells that the process above it how to access it
 It specifies what the parameters (values) are and what results to expect. It too
says nothing about how the layer works inside (encapsulation).

33. OSI reference model

34. OSI reference model-summary
Applicationlayer Provides electronic mail, file transfers and
other user services.
Presentationlayer Translates data formats, encrypts and
decrypts data.
Sessionlayer Synchronizes communicating users, re4covers
from errors, bracket operations.
Transport layer Determines network, may assemble and
resemble packets.
Network layer Determines, routes, manages billing
information.
Data link layer Detects or corrects errors, defines frames.
Physical layer Transmits physical data.
Physical layer (designissues)
 Make sure that when one side sends a 1 bit, it is received by the other side as 1 bit, not
as 0 bit.
 How many volts should be used to represent a 1 and how many for 0.
 How many seconds a bit lasts.
 Whether transmission may proceed simultaneously in both directions.
 How many initial connection is established and how it is torn down when both sides are
finished.
 How many pins the network connector has and what each pin is used for.
PHYSICAL LAYER
It transmits bits of information across a link.
Deals with the problem such as:
o Size and shape of connectors
o Assignment of functions to pins
o Conversion of bits to electrical signals
o Bit level synchronization.
It is usual for several different types of physical layers to exist within a network and even for
multiple different types of physical layers to exist within a node. Because, each technology
requires its own physical layer.

35. DATA LINKLAYER
Transmits chunks (groups) of information across a link creates and recognizes frame
boundaries.
Solves the problems caused by damaged lost and duplicate frames.
Traffic flow regulation and error handling.
Control access to the shared channel in broadcast networks.
NETWORKLAYER
Enables any pair of systems in the network to communicate each other.
Controls the operation of the subnet.
 How packets are routed from source to destination
 How to control traffic congestion
Maintains accounting information.
Manages network interconnection.
 Addressing
 Packet size
TRANSPORTLAYER
Establishes a reliable communication stream between pair of system.
Deals with errors that can be introduced by the network layer.
 Lost of packets
 Duplicated packets
 Packet reordering
 Fragmentation and reassembly
Accepts data from the session layer, split it up into small units. If necessary pass them to the
network layer and ensure that all pieces arrive correctly at the other end.
Creates and maintains network connection required by session layer.
May multiplex several network connections.
True end to end layer from source to destination.
SESSION LAYER
Allows user on different machines to establish sessions between them.
Provides session services:
 Token management
 Synchronization

36. PRESENTATION LAYER
Concerned with the syntax (rules) and semantics (forms) of the information transmitted.
Does encoding and decoding.
APPLICATION LAYER
Contains variety of protocols that are commonly needed.
It is common for multiple applications to be running concurrently in a node.
 Application
 File transfer
 Virtual terminal
 Web browsing
PDU (Protocol Data Unit)
Each layer communicates with its peer layer through its PDU (Protocol Data Unit).
SDU (Service Data Unit)
When n+1 gives information to layer n for transmission the information is known as SDU
(Service Data Unit).

37. TCP/IP reference model
This consists of 04 layers.
1. Application layer
2. Transport layer
3. Internet layer
4. Host-to-network layer
1. Application layer
Application layer consists of all high level protocols.
 Virtual terminal TELNET
 File transfer FTP
 Electronic mail SMTP
 Domain name server (DNS)
 HTTP

2. Transport layer
Transport layer same as in OSI transport layer, it allows peer entities on the source and
destination host to carry on a conversation.
Protocols: - TCP & UDP
3. Internet layer
Connectionless
Packet switching
Defines official packet format.
Deliver IP packets where they are supposed to go.
Vulnerabilities of network
This can be categorized as,
1. Threats
2. Attacks
3. Malware
1. Threats
 Spoofing
 Tampering
 Repudiation
 Information disclosure
 Denial of service
 Elevation of privilege
 Phishing
 Port scan

38.  Spoofing
Is a situation in which one person or program successfully masquerades as
another by falsifying data and thereby gaining an illegitimate advantage.
 Tampering
A person commits the offense of tampering with computer data if he or she
knowingly and without authorization or without reasonable grounds to believe
that he has such authorization.
 Repudiation
this attack can be used to change the authoring information of actions executed
by a malicious user in order to log wrong data to log files.
 Informationdisclosure
information disclosure enables an attacker to gain valuable information about a
system.
 Denial of service
Is an attempt to make a machine or network resource unavailable to its intended
users.
A DoS attack generally consists of efforts to temporarily or indefinitely interrupt
or suspend services of a host connected to the internet.
DDoS attacks are send by two or more people.
DoS attacks are send by one person or system.
 Elevationof privilege
Actions of privileges- view, edit, modify system files.
Privilege escalation means a user receives privileges they are not entitled.
VERTICAL PRIVILEGE ESCALATION
also known as privilege escalation, where a lower privilege user or application
accesses functions or content reserved for higher privilege users or applications.
(eg;- internet banking users can access site administrative functions or the
passwords for a Smartphone can be bypassed. )
 Phishing

39.  Port scan