Transcript Data communication networks

INTRODUCTION TO DATA COMMUNICATION NETWORKS
1.1 INTRODUCTION
In data communications world
•data is defined as information that is stored in digital
form. The word data is plural. Singular unit is datum.
•Information is defined as knowledge or intelligence.
The information that has been processed, organized and
stored is called data.
The process of data communication involves
Transmission, Processing and Reception of data
The source information may be either in analog or digital form. If the
information is in analog form then it is converted into digital form by using
an Analog to digital converter, then transmitted.
Receiver is again converted the signal from the digital form to the analog
form by using a digital to analog converter.
A Network is a set of devices (nodes or stations) interconnected by
media links.
Data communication networks are systems of interrelated computer and
computer equipment and can be as simple as a pc connected to a printer
or two pc’s connected together through the public telephone network.
On the other hand this network can also be a complex communication
system comprised of one or more mainframe computers and hundreds,
thousands or millions of remote terminals, personal computers and
workstations. There is no limit to the capacity or size of a data
communication.
Uses of Data communication networks
• To interconnect virtually all kinds of digital computing equipment from
automatic teller machines (ATMs) to bank computers
• Personal computers to information highways, such as the Internet and
workstations to mainframe computers.
•
airline
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Hotel reservation systems
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Mass media and news network
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Electronic mail delivery systems.
1.2 STANDARDS ORGANIZATIONS FOR DATA
COMMUNICATIONS:
• A group of organizations, governments, manufacturers and users meet on
a regular basis to ensure an orderly flow of information within data
communications networks and systems establishing guidelines and
standards.
• The main intention is that all the data communication equipment
manufacturers and users should fulfill these standards.
• The most prominent organizations relied on in North America to publish
standards and make recommendations for the data, telecommunications and
networking industries are shown in fig:
ISO
ITU-T
IEEE
ANSI
EIA
IAB
IETF
IRTF
TIA
International Standards Organization (ISO)
 Created in 1946, ISO is a voluntary, nontreaty organization whose
membership consists of mainly members from the standards committees of
various governments throughout the world.
 The ISO creates the sets of rules and standards for graphics and
document exchange.
 Provides models for equipment and system compatibility, quality
enhancement, improved productivity and reduced costs.
 Responsible for endorsing and coordinating the work of the other
standards organizations.
International Telecommunications UnionTelecommunications Sector (ITU-T)
 It is one of the four permanent parts of the International
telecommunications union based in Geneva and Switzerland.
 Membership consists of government authorities and representatives
from many countries.
 Standard organization for United Nations.
 Develops the recommended sets of rules and standards for telephone
and data communications.
The ITU-T is developed into 14 study groups that prepare
recommendations on the following topics:
•Network and service operation
•Tariff and accounting principles
•Telecommunications management network and network maintenance
•Protection against electromagnetic environment effects
•Data networks and open system communications
•Characteristics of telemetric systems
•Television and sound transmission
•Language and general software aspects for telecommunications systems
•Signaling requirements and protocols
•End-to-end transmission performance of networks and terminals
•General network aspects
•Transport networks, systems and equipment
•Multimedia services and systems
Institute of Electrical and Electronics Engineers
(IEEE)
 An International professional organization
 Founded in the United States
 Comprises of electronics, computer and communication engineers
 Consists of over 200,000 members
 Works closely with ANSI to develop communications and information
processing standards
 Goal is advancing theory, creativity and product quality in any field
associated with electrical engineering.
American National Standards Institute (ANSI)
 Standard organization for United States and is the U.S voting
representative for the ISO
 It is a private, non profit organization
 Consists of equipment manufacturers and users of data processing
equipment and services
 Membership consists of people from professional societies, industry
associations, government and regulatory bodies and consumer groups
Electronics Industry Association (EIA)
 It is a nonprofit U.S trade association
 Establishes and recommends industrial standards
 Develops standards in the field of telecommunication and increases
public awareness
Telecommunications Industry Association (TIA)
 It is a leading trade association in the field of communications and
information technology industry.
Develops trade promotion, trade shows, domestic and international
support.
Acts as a junction for new communication networks.
Internet Architecture Board (IAB)
 Oversees the architecture protocols and procedures used by the internet
Manages the processes used to create the internet standards
Serves as an appeal board for complaints of improper execution of the
standardization processes
Responsible for administration of various internet assigned numbers
Acts as representative for internet society in relation with other
organizations concerned with standards and other technical
organizations relevant to world wide internet
 Acts as a source of advice and guidance to the board of trustees and
officers of the internet society
Internet Engineering Task Force (IETF)
 It is a community of designers, operators, vendors and researchers
concerned with the evolution of internet architecture and the smooth
operation of internet
Internet Research Task Force (IRTF)
 It promotes the importance of research for the evolution of future
internet related to internet protocols, applications, architecture and
technology
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Briefly explain the network architecture
of data communication networks
NETWORK ARCHITECTURE
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It defines the product and services required by individual components
with in system to operate together for achieving desired results
It comprises of set of equipments, transmission media, procedures and
functions
Goal of network architecture
 To perform inter process communication among users and processors
 To provide sharing of resources
 To perform centralized control for geographically system
 To provide compatibility of dissimilar equipment and software
 To perform centralized management and allocation of network resources
 To perform distribution of processing functions
 To perform data flow control
 To provide network tools to network users for setting up network
Functional responsibilities of network architecture
 Electrical specifications
 Hardware arrangements
 Software procedures
Network protocols
 Protocol: set of rules or guidelines for communication between DTEs
Functions of protocol
 Communication startup
 Character identification and framing
 Message identification
 Line control
 Error control
 Termination
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The protocols for network architecture are of three types
Current protocols: most updated and sophisticated networks and
protocols
Legacy protocols: protocols which are used oftenly
Legendry: protocols which are wiped off on the one which gets
disappeared
Data networks are classified in to two types
1.
Broad cast networks
2.
Point – to – Point network
Broadcast networks
It share a single common communication channel
In this data is transmitted in the form of short messages called
frames, blocks or packets
All devices connected to the channel receives the message/packets
through this network. It is called broadcasting
It is also known as multipoint or multidrop connection
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When messages are intended for specific group of stations it is called as
multicasting
In this each data packet contains address of receiving station
Transmitter
Station 1
Common channel
Station 2
Station 3
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Point – to – Point networks:
It has only two stages
A dedicated communication channel between two stations
Messages transmitted from one station are received by other station
through a single channel and vice versa
Hence no address is needed on data packets
The channel capacity is shared between two stations only
Data can be transmitted at longer distance with continuous transmission
Dedicated channel
 Write
about layered network
architecture?
 Explain
protocols data unit with neat
diagram?
LAYERED NETWORK ARCHITECTURE:
Source computer
Network
Destination computer
Peer to Peer communication
LAYER N+1
LAYER N+1
LAYER N
LAYER N
LAYER N-1
LAYER N-1
To avoid complexity, the network architecture is organized as a series of
layers or levels.
It is referred as layered network architecture
It differs from network to network
The function of each layer is to provide services to the layer above by
adding value to the services provided by the lower layers
Here the layer N provides services to the layer N+1 by adding value to the
services offered by the layer N-1
Layer of Host 1 can communicate with layer N of Host 2
Advantage: It provides peer-to-peer communications protocols where a
given layer in one system (source) can logically communicate with its
corresponding layer in another system (destination). This allows different
computers to communicate at different levels
Protocol data unit (PDU)
User information
Layer N PDU
Overhead
Header
Overhead
Trailer
User information
Layer N PDU
With layered architectures, communications between two
corresponding layers requires a unit of data called a protocol data
unit (PDU). As shown in the above figure a PDU can be a header
added at the beginning of the message or a trailer appended to the
end of a message.
In layered architecture, communication occurs between two
similar layers. However data must flow through the other layers.
Data flows downward through the layers in the source system and
upwards through the layers in the destination system.
Due to the technological advances in the layered architecture, it is
easy to modify one layer’s protocol without having to modify all the
other layers. Each layer is essentially independent of the other layer.
Therefore, the functions in lower layers are removed entirely from
the software tasks and replaced in the hardware.
Disadvantage: Tremendous amount of overhead is required.
System – A
(PDU-Data)
System – A
(PDU-Data)
LAYER N+1
PDU
Network
LAYER N+1
PDU
N+1 HEADER
Decapsulation
Encapsulation
LAYER N
PDU
LAYER N
PDU
N
Header
N
Header
Decapsulation
Encapsulation
LAYER N-1
PDU
N+1 HEADER
N-1
Header
Encapsulation
LAYER N-1
PDU
N-1
Header
Decapsulation
In intermediate systems, data flows upward first and then
downward. As data passes from one layer into another, headers and
trailers are added and removed from the PDU. The process of adding or
removing PDU information is called encapsulation / decapsulation
because it appears as though the PDU from the upper layer is
encapsulated in the PDU from the lower layer during the downward
movement and decapsulated during the upward movement
(Encapsulate means to place in a protected environment and decapsulate
means to remove from a protected environment.)
In a layered protocol, layer N receive services from the layer immediately
below it (N-1). Layer N can provide service to more than one entity in
layer N+1 by using a service access point (SAP) address to define for
which entity the service is intended. Information passes from one layered
architecture to another layer through a layer-to-layer interface. This
interface defines the information and the services the lower layer must
provide to the upper layer.
 Explain
in detail about the protocols
of network architecture?
Protocols of network architecture
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A protocol is a set of rules and regulations that a computer network must follow
while communicating with others
Protocols include network capabilities
 How much data can be sent
 How it will be sent
 How it will be addressed
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The protocols that governs the exchange of data within the network or a portion
of network are known as Data Communication Protocols
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The list of protocols used by a system is called a protocol stack. Only one
protocol is generally used for one layer
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Each layer has set of responsibilities that are
data transfer
data segmentation
sequence control
notification
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flow control
re-assembly
error detection and correction
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Explain elements of protocol?
ELEMENTS OF A PROTOCOL
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SYNTAX:
it is the format of data or the structure how it is presented.
Eg: first eight bits are for sender address, next eight bits are for receiver
address and rest of the bits for message data
SEMANTICS:
It is the meaning of each section of bits
Eg: the address bit means the route of transmission or final destination of
the message
TIMING:
At what time data can be sent and how fast data can be sent
STANDARDS
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Provide guidelines to the manufacturers, venders, government agencies and
service provider.
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It ensures the interconnectivity and compatibility of the device
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Standards help in maintaining market competitiveness and guarantees
interoperability
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Data communication standards are of two categories:
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De factpr: means facts or by convention. The standards that are not approved
by any established by manufacturers
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De jure: means by law or by regulation. These are the standards that are
recognized officially by an organization
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Explain briefly about types of protocols?
or
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Write the differences between connection
oriented and connection less protocols
Types of protocols:
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Connection oriented:
In connection oriented direct path is established between source and
destination
Eg: Telephone system
It provides a substantial amount of care for user data
These are designed to provide high degree of reliability for data moving
through the network
It is achieved by using a set of procedures for establishing the connection,
transferring the data, acknowledging the data and then clearing the
connection
In this each packet of data is assigned a unique sequence number and an
associated acknowledge number to track the data as they travel through a
network
If data are lost or damaged the destination station requests they be re-sent
Characteristics of connection oriented protocols
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A connection process called a handshake occurs between two stations
before any data are actually transmitted (these connections refer to as
sessions , virtual circuits or logical connections)
It requires some means of acknowledgment for transmission of data
These acknowledgment procedures provide a high level of network
reliability
It provides some means of error control whenever data are found to be in
error, the receiving station requests a re-transmission
When a connection is no longer is needed, a specific handshake drops the
connections
NETWORK
Setup request
Setup response
Data transmitted
Data acknowledgment
Connection clear request
Clear response
Connectionless protocols:
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In this the data is exchanged in a unplanned fashion without prior coordination between end points
These protocols do not provide high degree of reliability
It provides a significant advantage in transmission speed
Eg: US postal service
Characteristics of connectionless protocols:
These protocols send data with a source and destination address without a
handshake
These protocols do not support error control or acknowledgment procedures
It makes an unreliable method of data transmission
NETWORK
data
data
data
data
data
S.No
Connection oriented protocols
Connectionless protocols
1
Circuit setup is required
Circuit setup is not required
2
Each packet contains a short virtual
circuit number
Each packet contains the full
source and destination address
3
All packets follow the same route
Each packet is routed
independently
4
Handshake and acknowledgment
signal is required for data transmission
Handshake and acknowledgment
signal is not required for data
transmission
5
In case of route failure all packets that
are passed are terminated
Only crashed packets lost
6
Error control is possible
It does not support error control
7
It is less efficient
It is more efficient
8
Speed of transmission is slow
Speed of transmission is
significantly high
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More reliable mode of transmission
Less liable mode of transmission
10
Congestion control is easy using
buffers
Difficult congestion control
11
Analogous to telephone system
Analogous to postal system
Explain briefly about OSI model?
or
Explain briefly about open system
interconnection
1.4 OPEN SYSTEMS INTERCONNECTION (OSI)

OSI is the name for the set of standards for communicating among
computers.
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The OSI standards serve as structural guide line for exchanging
information between computers, workstations and networks.
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In 1983, the ISO and the ITU-T adopted a seven- layer
communications architecture reference model. Each layer consists of
specific protocols for communicating.
The hierarchy provides intercommunication of data processing
equipment by separating network responsibilities into seven distinct
layers.
As with the layered architecture, overhead information is added
to a PDU in the form of headers and trailers. If all the seven levels of the
OSI model are addressed, less than 15% of the transmitted message
contains the source information, the rest is the overhead.
Levels 4 to 7 in the layers address the applications aspects of the
network that allow for two host computers to communicate directly. The
bottom layers are concerned with the actual mechanics of moving data
from one machine to another.
Data transmission through OSI LAYER
1. Physical layer
 Lowest level of the OSI hierarchy
 Responsible for the actual propagation of unstructured data bits (1s and 0s)
through a transmission medium
 Specifies the type of transmission medium and the transmission mode (simplex,
half duplex or full duplex) and the physical, electrical, functional and procedural
standards for accessing data communication networks
 Connections, pin assignments, interface parameters, timing, maximum and
minimum voltage levels and circuit impedances are made at the physical level
 Transmission media defined by the physical layer include metallic cable, optical
fiber cable, or wireless radio-wave propagation.
 Connectivity devices connect devices on cabled networks
 This layer includes the carrier system used to propagate the data signals
between the points in the network
 Data is carried in a communication system using either metallic or optical fiber
cables or wireless arrangements such as microwave, satellites and cellular radio
systems. The carrier uses analog or digital signals that are encoded and then
propagated through the system
2 Data-link layer
Responsible for providing error-free communication across the physical
link connecting primary and secondary stations (nodes) within a network.
packages data from the physical layer into groups called blocks, frames, or
packets
provides a means to activate, maintain and deactivate the data
communications link between nodes
provides the final framing of the information signal, synchronization,
facilitates the orderly flow of data between nodes, outline procedures for
error detection and correction and provides the physical addressing
information
3.Network layer
 Provides details that enable data to be routed between devices in an
environment using multiple networks, sub networks or both.
 Components used are routers and their software.
 Determines which network configuration is most appropriate for the
function provided by the network and addresses and routes data within
networks by establishing, maintaining and terminating connections
between them.
 Provides the upper layers of the hierarchy independence from the
data transmission and switching technologies used to interconnect
systems.
 Performs the above task by breaking the messages into smaller data
packets, routing them from a sending node to a receiving node within a
data communication network.
 Provides the source and destination network addresses, subnet
information and source and destination node addresses.
4.Transport Layer
 Controls and ensures the end-to-end reliability of the data message
propagated through the network between two devices.
 Provides the reliable, transparent transfer of data between two end
points.
 Performs message routing, segmenting, error recovery.
 Highest layer in the OSI hierarchy in terms of communications.
 Provides data tracking, connection flow control, sequencing of data,
error checking and application addressing and identification
5. Session Layer
 Responsible for network availability (data storage and processor
capacity)
 Provide the logical connection entities at the application layer
 Includes file transfer protocols and sending e-mail
 Regular tasks include network log-on and log-off procedures and user
authentication
 It is a temporary condition that exists when data are actually in the
process of being transferred
 Determines the type of channel communication available (simplex, half
duplex, duplex)
Characteristics are
Virtual connections between applications entities
Synchronization of data flow for recovery purposes
Creation of dialogue units and activity units
Partitioning services into functional groups
6. Presentation Layer
 Provides independence to the application processes by addressing any
code or syntax conversion necessary to present the data to the network in
a common communications format
 Specifies how end-user applications should format the data
 Provides for translation between local representations of data and the
representation of data that will be used for transfer between end users (ex:
encryption, data compression and virtual terminals)
 Translates b/w different data formats and protocols
 Functions include data file formatting, encoding, encryption and decryption
of data messages, communication procedures, data compression
algorithms, synchronization, interruption and termination
 Performs code and character set translation (including ASCII &EBCDIC),
formatting information
 Determines display mechanism for messages
7. Application Layer
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Highest layer in the hierarchy
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Provides access to the OSI environment
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Provides distributed information services
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Controls the sequence of activities with an application and their
sequence of events b/w the computer application and the user of
another application
Communicates directly with the user’s application program
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User application processes require application layer service elements to
access the networking environment.
There are two types of service elements:
CASE ‘s (Common application service elements): These are
useful to a variety of application processes.
Ex: association control that establishes, maintains and terminates
connections with a peer application entity and commitment,
concurrence and recovery that ensure the integrity of distributed
transactions
SASE’s( Specific application service elements): These satisfy
particular needs of application processes.
Ex: FTP (file transfer protocol), SNMP (simple network management
protocol), Telnet (virtual terminal protocol &SMTP (simple mail transfer
protocol)
DATA COMMUNICATION CIRCUITS
 Data communications circuits use the electronic communications
equipment and help to interconnect digital computer equipment.
 The communication equipment may be any type of physical
transmission media or wireless radio system in existence.
 Communication facilities are provided to the data communication
users through public telephone networks (PTN), public data networks
(PDN) and a large no. of private data communications systems.
Digital
Information
Source
Transmitter
Transmission
medium
Receiver
Digital
Information
Destination
Source:
 The information source generates data.
 The source equipment provides a means for humans to enter
data into the system.
 The source could be a mainframe computer, personal computer,
workstation, or nearly any piece of digital equipment.
Transmitter:
 The transmitter acts as an interface between source equipment
and the transmission medium.
 It receives information from the source in the digital form,
encodes it and then propagates it through a transmitter into the
transmission medium.
Transmission medium:
 The transmission medium carries these encoded signals from the
transmitter to the receiver.
There are different types of transmitting media such as free-space radio
transmission (wireless, terrestrial, microwave, satellite radio and cellular
telephone) and physical facilities such as metallic and optical fiber cables.
Receiver:
The receiver receives the encoded signals from the transmission medium, decodes
them and sends them to the destination.
The receiver acts as an interface between the transmission medium and the
destination equipment.
Destination:
 Like source, destination could also be a mainframe computer, personal computer,
workstation or virtually any piece of digital equipment.
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What are the merits and demerits of
serial and parallel data transmission?
SERIAL AND PARALLEL DATA TRANSMISSION
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In parallel Transmission of all the bits present in the data is done at a time
because each bit will be provided its own transmission line.
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This type of transmission is called parallel by bit or serial by character
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In serial transmission, there will be only one transmission line and the bits
present in the data can be transmitted one after the other only.
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This type of transmission is called serial by bit.
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The trade-off between serial and parallel transmission is speed versus
simplicity. Data transmission can be done much more rapidly using parallel
transmission.
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Parallel transmission requires more no. of transmission lines.
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Parallel transmission is used for short distance data communications
serial transmission is used for long distance data communications.
data
0
1
1
0
Serial data transmission
Parallel data transmission
0
1
1
0
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Serial data transmission:
Merits :
require only one transmission line to transmit data
Used for long distance communication
Data transmission is simple
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Demerits:
transmission is very slow i.e. only one bit can be transmitted
at a time
It requires four clock pulses to transmit four bit code
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Parallel data transmission:
Merits:
speed of data transmission is more
Require only ‘1’ clock pulse to transmit the four – bit code
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Demerits:
used for short distance transmission i.e. with in the electronic
device
Require more transmission lines to transmit the data
DATA COMMUNICATIONS CIRCUIT ARRANGEMENTS
Data communications circuits can be configured based on
The specifications of the circuit
The no. of stations on the circuit
Type of transmission facility
Distance between stations
No. of users at each station
Circuit Configurations
Data communications networks are of two types:
Two point configuration involves only two locations or stations.
A two-point circuit involves the transfer of digital information between a mainframe
computer and a personal computer, two main frame computers, two personal
computers or two data communication networks
Multipoint configuration involves three or more stations.
A multipoint network is generally used to interconnect a single mainframe computer
to many personal computers or to interconnect many personal computers.
Regardless, of the configuration each station can have one or more computers,
computer terminals, or workstations.
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Write a short notes on different modes of
transmission?
Transmission Modes
Simplex:
Data transmission is unidirectional
Simplex lines are also called receive-only or transmit- only or one-way lines
Half duplex:
Data transmission is possible in both directions but not at the same time.
HDX lines are also called two-way-alternate or either-way lines.
Full duplex:
Transmissions are possible in both the directions simultaneously, but they must
be between the two stations.
FDX lines are also called two-way simultaneous, duplex or both-way lines
Full/full duplex:
Transmission is possible in both directions at the same time but not between the
same two stations.
F/FDX is possible only on multipoint circuits.
DATA COMMUNICATIONS NETWORKS
The factors involved while designing a computer network are:
1. Network goals as defined by organizational management
2. Network security
3. Network uptime requirements
4. Network response time requirements
5. Network and resource costs
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Explain the functions and features of data
communication network components?
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Basic components of a data communication network are
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End station is
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Applications
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Networks
SERVICES
LAN
WAN
MAN
Network components, functions and features
1.
2.
3.
4.
5.
6.
7.
8.
9.
Servers
Clients
Transmission Media
Shared Data
Shared Printers And Other Peripherals
Hardware And Software Resources
Network Interface Card (NIC)
Local Operating System (LOS)
Network Operating system (NOS).
1. Servers
Servers are the computers that hold shared files, programs, and
the network operating system.
Servers provide access to network resources to all the users of
the network.
Ex: file servers, print servers, mail servers, communication
servers, database servers, directory/security servers, fax
servers and web servers etc
User
Computer
File request
File
Server
Copy of the requested file
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File servers are loaded with files, accounts and a record of the access rights
of users on the network.
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Server provides a shareable virtual disk to the users (clients)
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File mapping schemes are implemented to provide virtual ness of the files
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Security systems are installed and configured to provide the server with
the required security and protection for the files
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Redirector or shell software programs located on the user’s computers
transparently activate the client’s software on the file server
Different servers available in current days are
1. Exchange server
2. File server
3. DNS server
4. DFS server
5. Web server and many more
2. Clients
Clients are the computers that access the
Network
use the network
share the network resources
Client computers are basically the customers of the network, as they
request and receive services from the servers.
3. Transmission media
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These are the facilities to interconnect computers in a network
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Ex: twisted pair wire, optical cable, coaxial cable
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Transmission media are sometimes called channels links or lines
4. Shared Data
Shared data are data that file servers provide to clients, such as
data files
printer access programs
e-mail
5. Shared printers and other peripherals
Shared printers and peripherals are hardware resources provided to
the users of the network by servers.
Resources provided include
data files
printers
software
any other items used by clients on the network
6. Network Interface Card (NIC)
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NIC constructs, transmits, receives and processes data to and from a PC
and the connected network
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Each device connected to a network must have a NIC installed
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NIC is generally installed in a computer as a daughterboard
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Some manufacturers incorporate the NIC into the motherboard during
manufacturing
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Each NIC has a unique six-byte media access control address (MAC) which
is typically and permanently burned into the NIC when it is manufactured

The MAC address is some times called the physical, hardware, node,
Ethernet or LAN address

NIC must be compatible with the network to operate properly

NIC requires drivers to operate on the network
7. Local operating system (LOS)


A LOS allows personal computers to access files, print to a local printer and
have and use one or more disk and CD drives that are located on the
computer.
EX:
 MS-DOS, PC-DOS, UNIX, MACINTOSH,OS/2,WINDOWS 3.11,
WINDOWS 95, WINDOWS 98, WINDOWS 2000, LINUX
UNIX
MS-DOS
WINDOWS
MACINTOSH
PC
8. Network Operating System (NOS)



NOS is a program that runs on
computers and servers that allows the
computers to communicate over a
network.
Services provided are :
log-in features
password authentication
Printer access
Network administration functions
Data file sharing
NOS is a software that makes
communications over a network
manageable
Server
(NOS)
Server
(NOS)
Server
(NOS)
Characteristics of NOS

Allows users of a network to interface with the network properly

NOS commonly offers services like file service, print service, mail service,
communication service, database service, directory and security services

NOS determines whether data are intended for the user’s computer or
whether the data need to be redirected out onto the network

NOS implements clients software for the user which allows them to access
servers on the network

Popular NOS systems are UNIX, NOVELL NETWARE, APPLE SHARE,
MACINTOSH SYSTEM 7, IBM LAN SERVER, COMPAQ OPEN VMS,
MICROSOFT WINDOWS NT SERVER
PC
USER 2
PC
USER 3
PC
USER 4
PC
USER 1
PC
USER 5
HUB
COMMUNICATION
SERVER
NOS
DATA
BASE
SERVER
FILE
SERVER
MAIL
SERVER
PRINT
SERVER
DATA
BASE
SERVER
PRINTER


Discuss peer to peer client/server networks?
and
Discuss dedicated client/server networks?
or

Discuss briefly about network models?
Network models

Peer-to-peer client/server

Dedicated client/server
1. Peer-to-peer client/server network
• All computers share their resources, such as hard drives, printers and so on, with
all the other computers on the network
•Peer-to-peer operating system divides the time between servicing the
computer on which it is loaded and servicing requests from other computers
•This network is also called a work group
•There are no dedicated servers or hierarchy among the computers
CLIENT/SERVER1
(COMPUTER)
CLIENT/SERVER2
(COMPUTER)
HUB
CLIENT/SERVER3
(COMPUTER)
CLIENT/SERVER4
COMPUTER
Peer-to-peer client/server network - 2








In fig., all four clients/servers are connected through a hub
All computers are equal
Therefore the name given is peer
Each computer in the network can function as a client and/or a server
No single computer holds the network operating system or shared files
No computer is assigned network administrative tasks
Users at each computer determine which data on their computer are shared with
the other computers on the network
This network can be used only
 when there are a few users (approx 10) on the network
 when all the computers are located in the same general area
 When security is not an issue
 When there is limited growth projected for the network in the immediate future
Peer-to-peer client/server network
These networks should be small for the following reasons:
When operating in the server role, the operating system is not optimized to
efficiently handle multiple simultaneous request
 The end user’s performance as a client would be degraded
 Administrative issues such as security, data backups, and data ownership may
be compromised in a large peer-to-peer network
2. Dedicated client/server network

One computer is designated as the server and the rest as clients

As network grows additional computers can be designated servers

The designated servers function only as servers and are not used as a client or
workstation

The servers store all the network’s shared files and applications programs such
as word processor documents, compilers, database applications, spread
sheets and the network operating system

Client computers can access the servers and have shared files transferred to
them over the transmission medium
client1
Client 2
Client 3
hub
Dedicated
File
Server
Dedicated
Print
Server
PRINTER
Dedicated
Mail
Server
Dedicated client/server network -2

Each client can access the resources on any of the servers and also the
resources on other client computers

There can be a separate dedicated server for each function or one single
general purpose server responsible for all services

In some client/server networks, client computers submit jobs to one of the
servers.

The server runs the software and completes the job and then sends the
results back to the client computer

With this network, less information propagates through the network than with
the file server configuration because only data and not applications
programs are transferred between computers

Write about data communication
hardware?
DATA COMMUNICATIONS HARDWARE

COMPARISION BETWEEN HUMAN SPEECH COMMUNICATION AND DATA
COMMUNICATION
ELECTRICAL
ACOUSTICAL ENERGY
ENERGY
ELECTRICAL
ENERGY
ACOUSTICAL
ENERGY
TELEPHONE
TELEPHONE SET
NETWORK
TELEPHONE SET
HUMAN2
HUMAN1
FIG A
ANALOG
ELECTRICAL
ENERGY
FIG B
ANALOG
ELECTRICAL
ENERGY
DIGITAL DATA
DIGITAL DATA
TELEPHONE
TRANSCEIVER
TELCO
INTERFACE
NETWORK
TELCO
INTERFACE
TRANSCEIVER







FIG A shows how two humans communicate over the telephone network
using standard analog telephone sets
The telephone sets interface human speech signals to the telephone
network and vice versa
At the transmit end, the telephone set converts acoustical energy to
electrical energy
At the receive end, the telephone set converts electrical back to
acoustical energy
FIG B shows how digital data are transported over the telephone
network
At the transmit end, a telephone interface converts digital data from the
transceiver to analog electrical energy which is transported through the
telephone network
At the receiving end, the telephone interface converts the analog
electrical energy received from the telephone network back to digital
data
DATA COMMUNICATIONS HARDWARE

A data communication system can be described as connecting two endpoints
through a communication channel

It comprises of
 Transmitter (source)
 Transmission path (data channel)
 Receiver (destination)

The two end points
 may not possess the same capabilities
 must be configured with the same basic components
 equipped with special devices that perform unique functions
 Make the physical connection to the data channel
 Process the data before they are transmitted and after they have been
received

All the end points must have three fundamental components:
 DATA TERMINAL EQUIPMENT (DTE)
 DATA COMMUNICATIONS EQUIPMENT (DCE)
 SERIAL INTERFACE
DATA TERMINAL EQUIPMENT:

It is also known as information originator or information terminator

It is a binary digital device that perform different functions such as
1. generation,
2. transmission,
3.
reception or interpretation of data message

DTES are the data communication analogous to person in a telephone
conversation

It contains necessary hardware and software to establish and control
communication between endpoints in a communication system

DTES of one system directly communicates with other DTES

DTES include the concept of terminals, clients, hosts and servers

The devices that are used to input, output and display information such
as keyboard, printer and monitor respectively are termed as terminals

A terminal with enhanced computing capabilities is called a client

High capacity mainframe computers that are used to support terminals
are hosts

These hosts with lower storage capacity and less computing capability
are generally termed as servers

Servers and hosts maintain local databases and programs

They distribute information to clients and terminals

Examples of DTE are Video display terminals, personal computers,
and printers

DATA COMMUNICATION EQUIPMENT(DCE):

DCES are devices that are used to interface data terminal equipment
(DTE) and transmission channel

Examples of DCE includes T1 carrier or an analog telephone circuit

The output of DTE is based upon the type of application used i.e.,
analog application or digital application

In general DCE is transducer which converts DTE signals to a form
more suitable to be transmitted over transmission channel and reconverting these signals to original form at the receiving end

Data communication between DTES is major functions of DCES

They are independent of content of data


Depending upon the type of transmission channel used the DCES
are classified as
1.
CHANNEL SERVICE UNITS (CSUS)
2.
DIGITAL SERVICE UNITS (DSUS)
3.
DATA MODEMS
4.
DATA MODEMS are used to interface analog telephone
networks and DTES whereas CSUS and DSUS are used to
interface digital transmission channel and DTES
DCES are also termed as data circuit terminating equipment

SERIAL INTERFACE:

Serial interfaces are used for transmission of data between DTE and
DCE

It performs different functions such as coordinating the flow of data,
control signals and timing information between DTE and DCE

Different renders use different serial interfaces for connecting DTE and
DCE depending upon the type of connection, the size of connection and
voltage levels

Examples of serial interface include RS-232 family, they are RS232c,
RS232Dand rs232E

RS-232C was the third version of RS-232

It was published in 1987 whereas RS-232D and RS232E were
introduced in early 1990’s

Difference between RS-232D and RS-232E standards in their pin
designations

The RS-232D standard is sometimes referred to as EIA-232

The serial standards discussed above must provide the following
features
1.
Functional description of each signal on the interface
Standard cable and cable connectors
A specific range of voltages for transmission and reception signal
levels
Limitations for electrical parameters of the transmission line. The
electrical parameters include source and load impedance and cable
capacitance
2.
3.
4.
DATA COMMUNICATION HARDWARE CIRCUITS

There is distance limitation for connecting two devices over long
distance.
 Coaxial cable and twisted pair cable support upto few km distance.
 Signals become weak and noise is added
 The quality of the signals gets damaged

To overcome this problem, signal converting unit (SCU) is used to
amplify or regenerate the signal

Signal converting unit apply one of the following functions and bring the
signal to the original one
 SCU regenerating signal
 SCU amplify the signal
 It uses some modulation techniques
 Equalization of media characteristics





SCU which supports these functions are modem, optical transceiver, digital
service unit and line drivers
A pair of these devices always required one at each end
This pair of devices is called relay
It takes electrical signal as input from one end and deliver the same signals at
the other end
Transmission medium may be co-axial cable or fiber optical cable or twisted pair
device1
device2
Physical
layer
Physical
layer
interface
interface
SCU
Transmission
medium
SCU
Transmission
medium
Transmission
medium
INTERFACE STANDARDS

A successful and useful interface standard must define the lowest level
details of the interface, such as voltage values, the shape of the signals,
and the performance of the interface under many normal and abnormal
conditions

Specifications of physical layers are
 Mechanical specification
 Electrical specification
 Functional specification
 Procedural specification

Mechanical specification specify the connector, assignment of
interchange circuits to pins, size and dimensions etc

Electrical specification specify the voltage level and type
of signal to be transmitted in either direction between
DTE and DCE

Procedural specification specify how the control signals
are exchanged and in which sequence

Following standards work at physical layer



ETA: EITA 232 D, RS-449, RS-422A
CCITT: X.20, X.21, V.24, V.35, V.28
ISO: ISO 2110
DTE – DCE INTERFACE


DCE means data circuit terminating equipment i.e., modem
DTE means data terminal equipment i.e., computer
DTE
Station A
DCE
COMMUNICATION
NETWORK
DCE
DTE
Station B

The computing system of the DTE contains software needed to establish and
control the communication link between the primary and secondary station

An application program used by the DTE called a protocol

DCE is responsible for transmitting and receiving bits, one at a time, over a
transmission medium

Interface define mechanical, electrical functional and procedural characteristics

1. mechanical characteristics define the actual physical connection of the DTE to
the DCE
2. Electrical characteristics define the voltage level and timing of voltage
changes
3. functional characteristics define the functions that are performed by assigning
meanings to each of the interchange circuit. Functions are data, control timing,
electrical ground etc
4. procedural characteristics specify the sequence of events for transmitting
data, based on the functional characteristics of the interface



SERIAL INTERFACES



A standard serial interface is used to interconnect DTE and DCE
It ensures orderly flow of data between a DTE and DCE
It coordinates the flow of data, control signals and timing information
between the DTE and the DCE
CHARACTER SYNCHRONIZATION

Synchronize means to harmonize, coincide or agree in time

There are different types of synchronization in data communication
systems

Modem synchronization : recovering the carrier reference (both
frequency and phase). It is necessary for coherent demodulation

Clock synchronization : simply duplicating the transmit clock in the
receiver

Character synchronization : involves identifying the beginning and end of
character with in a message

Message synchronization : identifying the beginning and end of the
actual message, which embedded with in a more complex data
transmission

Modes of data transmission is divided in to two types
 Asynchronous
 Synchronous
transmission
transmission
Asynchronous transmission

Some times called start/stop transmission

In asynchronous transmission, bits are divided in to small groups and sent
independently.

The sender can send the groups at any time but the receiver never knows when
they will arrive

To alert the receiver to the arrival of a new group, there fore an extra bit is
added to the beginning of each byte which is called as start bit
The start bit is always ‘0’


To let the receiver know that the byte is finished, one or more additional bits are
added to the end of the byte. These bits are called stop bits

Asynchronous transmission is typical of byte-oriented input output

In this the data transferred is byte at a time

The start and stop bits identify the beginning and end of the character

There is a problem with asynchronous transmission i.e., the receiver
does not know when data will arrive until it gets there

Asynchronous transmission is designed for use with slow devices such as
keyboard and some printers

It also has high overhead
1 bit
or 2 bits
Transmitter
Stop
bit
1 bit
Data
8 bits
Start
bit
Receiver
Data or
parity bit
(odd/even)
(1)
(1)
Stop bits
(1,1.5,or 2)
1 or 0
Or b7
(MSB)
Start bit
b6
MSB
b5
b4
Data bits
b3
(5 to 8)
b2
b1
b0
LSB
0
Advantages :

Very inexpensive to implement

It can provide required performance at low cost

Both sides buffering is not required
Disadvantages :

Performance is poor

Efficiency is low

Considerable amount of communication time is lost between character
Synchronous transmission

With Synchronous transmission

Larger bit groups are sent

Instead of sending many characters separately, each with its own start
and stop bit, they are grouped together and then transmitted as a
whole

The group of data is called data frame or frame

In this, transmission is carried out under the control of timing source

The first part of frame contains SYN characters

SYN character is similar to start bit

Unique bit patterns are used to alert the receiver that a frame is arriving
Transmitter
Data
SYN
character
Receiver

The data bit defines the information being sent

No start bits and stop bits between the characters

The error checking bits are used to detect and correct transmission
errors

It is useful for high speed application

Synchronous transmission is much faster than asynchronous
transmission
Advantages :




Capable for high performance
Efficiency is high
Error checking and acknowledgement schemes work well
Data transfer rate is high
Disadvantages :


Expensive to implement
Both sides needs buffering
Differences between asynchronous and synchronous
transmission
S.NO
Asynchronous transmission
Synchronous transmission
1
Single character is sent
Group of character is sent
2
Very inexpensive to implement
Expensive to implement
3
Efficiency is low
Efficiency is high
4
Performance is poor
Capable for high performance
5
Low cost
Cost is high
6
Data transfer rate is low
Data transfer rate is high
7
Both sides buffering is not required Both sides need buffering
8
Error checking and
acknowledgement schemes is not
used
Error checking and
acknowledgement schemes works
well