DCCN Unit 1.pdf

DATA COMMUNICATION
AND
Course Instructor: Dr. C. Sreedhar
AND
COMPUTER NETWORKS
Some contents are copied from Internet sources
Unit - I

Unit 1
Introduction:
 Data Communication, Components,
 Data Representations, Dataflow,
 Network Topologies, categories of networks,
 Internet, protocols and standards.
 Internet, protocols and standards.
Network Models:
 Layered tasks, OSI Reference model, layers in OSI model,
 TCP/IP Protocol suite,
Addressing –
Physical address, Logical address, port

Unit 1
 Data Communications
 Definition
 Components of DC
 Data representation
Data flow
 Protocols and
Standards
 Definition
Standards
 Data flow
 Networks
 Network criteria
 Types of connections
 Categories of topology
 Network Models
 Standards

Data Communication: Definition
 Data communications
are the exchange of
data between two
data between two
devices via some
form of transmission
medium such as a
wire cable.

Data Communication
 The effectiveness of a data communications system depends
on four fundamental characteristics:
 Delivery: deliver data to the correct destination
 Accuracy: system must deliver the data accurately
 Timeliness: system must deliver data in a timely manner
 Jitter: refers to the variation in the packet arrival time

Data Communication: Components
 Five components
1. Sender
2. Message
3. Transmission
3. Transmission
medium
4. Protocol
5. Receiver

Protocol & its elements
 Definition: Set of rules that governs data communications.
 Syntax
 Structure or format of the data
 Indicates how to read the bits - field delineation
 Indicates how to read the bits - field delineation
 Semantics
 Interprets the meaning of the bits
 Knows which fields define what action
 Timing
 When data should be sent and what
 Speed at which data should be sent or speed at which it is being received.

Data communication components
 Sender
 Receiver
Message
 Message
 Transmission medium
 Protocol

Data Representation
 Text:
 Text is represented as a bit pattern.
 Unicode uses 32 bits to represent a symbol or character
 Numbers
 Numbers are also represented by bit patterns.
 Numbers are also represented by bit patterns.
 number is directly converted to a binary number
 Images
 Images are also represented by bit patterns.
 image is composed of a matrix of pixels
 each pixel is assigned a bit pattern.
 Audio and Video:

Data Flow
 Communication between two devices can be simplex or
half-duplex, or full-duplex

Networks
 A network is a set of devices (nodes) connected by
communication links.
 Node:
 Node:
 computer, printer, or any other device capable of
sending and/or receiving data.
 Link:
 can be a cable, air, optical fiber, or any medium which
can transport a signal carrying information.

Network Criteria
 Performance:
 Measured: transit time and response time
 Transit time: time required for a message to travel from AB
 Transit time: time required for a message to travel from AB
 Response time: elapsed time between inquiry and response
 Evaluated using two metrics:
 throughput and delay (more throughput and less delay).
 Reliability: measured by the frequency of failure
 Security: Network security issues include protecting data from
unauthorized access

Network Topology
 Physical Topology
 The way a network is laid out physically
 Two or more links form a topology
 Two or more links form a topology
 The topology of a network is the geometric
representation of the relationship of all the links
and linking devices (nodes) to one another.

Topology
 Physical topology
 Is how the wires are run
 The way in which a network is laid out physically
 Logical topology is how the signal travels.
 A device can be wired to implement any logical topology.
 A device can be wired to implement any logical topology.
 LANs are logical busses or rings, depending on how the hub is wired
 4 basic types: mesh, star, bus, ring
 The most common physical topology is the star.
 All the wires come back to a central point
 May often hybrid

Mesh Topology
 Every link is dedicated point-to-point link
 The term dedicated means that the link
carries traffic only between the two
carries traffic only between the two
devices it connects
 To link n devices fully connected mesh has:
n ( n - 1) / 2 physical channels (Full-Duplex)
 Every Device on the network must have
n - 1 ports

 Advantages
Each connection carry
its own data load (no
traffic problems)
 Disadvantages
Big amount of cabling
Big number of I/O ports
Installation and
Mesh Topology
traffic problems)
A mesh topology is
robust
Privacy or security
Fault identification
and fault isolation
Installation and
reconnection are difficult
Sheer bulk of the wiring
can be greater than the
available space
Hardware connect to each
I/O could be expensive

A star topology
each device needs only one link and one
I/O port to connect it to any number of
others
Advantages
less expensive than a mesh topology.
robust: If one link fails, only that link is
robust: If one link fails, only that link is
affected
Disadvantages
If the hub goes down, the whole system goes
down.
The star topology is used in local-area
networks (LANs)

bus topology
Nodes are connected to the bus cable by drop lines and taps
A drop line is a connection running between device and main cable.
A tap is a connector
A tap is a connector
One long cable acts as a backbone to link all the devices in a network
Advantages
bus uses less cabling than mesh or star topologies
Disadvantages
difficult reconnection and fault isolation
Signal reflection at the taps can cause degradation
a fault or break in the bus cable stops all transmission

Ring Topology
Each device has a dedicated point to point connection with only two devices on either
side of it.
Signal is passed along the ring in one direction till it reaches destination
Each device has a repeater
When a device receives signal to be passed, its repeater regenerates bits and
passes along.
Advantages
Easy to install and reconfigure
Fault isolation is simple
Disadvantages
Unidirectional traffic
Break in the ring disables entire network; solved by dual ring

A hybrid topology: a star backbone with three bus networks
Main Star topology with each branch connecting several stations in a
bus topology

Networks Categories
 Network category is determined by its size, ownership, the
distance it cover and its physical architecture

LAN: Local Area Network
 Privately owned and links the devices in a single office, building or campus
 LANs designed to allow resources to be shared between PCs or workstations. The
resources may be hardware or software.
 In LANs one of the computers has a large capacity drive and becomes a server to other
clients.
 Software stored on server and used as needed by the whole group.
23
 Software stored on server and used as needed by the whole group.
 LAN use only one type of transmission medium.
 The most common LAN topologies are bus, ring and star.
 LAN speed can be 100Mbps or 1000MBps(1G)

MAN: Metropolitan Area Network
 Owned by private company or it may be a service provided by public company (
such as local tel.-company)
 Extended over an entire city.
 May be single network such as a cable television network, or it may be connected
number of LANs into a large network so that resources may be shared LAN-TO-LAN.
 Examples:
24
 Examples:
 Company can use MAN to connect the LANs in all its offices throughout the city.
 A part of the telephone line network that can provide DSL line to the customer

WAN: Wide Area Networks
 Provides long distance transmission of data, voice , image and video
information over large areas ( country or whole world)
 In contrast to LAN, WAN may utilize public or private communication
equipment's or combination
25

LAN MAN WAN
LAN is a wired network, i.e., all the
computers and printers are connected
through wires.
The connections in MAN are connected
through modem or cables/ wires.
The network of WAN is
connected through broadband
services, 3G or 4G internet
services, etc.
The ownership of LAN is private.
Ownership of MAN might be public or
private.
private or public.
The internet speed of LAN is very high,
i.e., 1000 Mbps.
The sped of MAN is moderate, i.e., 44-155
Mbps.
The speed of WAN is relatively
less than MAN and LAN, i.e.,
150 Mbps.
26
The maintenance cost of LAN is easy. The maintenance cost of MAN is difficult.
The maintenance cost of WAN is
difficult.
The bandwidth of LAN is high. The bandwidth of MAN is less.
The bandwidth of WAN is
relatively low.
Examples:
 College
 School
 University
 Hospital
Examples:
 City
 Building
Examples:
 Broadband and internet
throughout the country or
continent.

Elements of Protocol
 Elements of a protocol:
 Syntax
 Semantics
 Timing
 Timing
Syntax: structure or format of data

Elements of protocol
 Semantics: meaning of each section of bits
Timing: when data should be sent and how fast they can be sent

Standards
 Two categories
 De facto: not approved by an organized body but adopted
 De jure: Legislated by an officially recognized body
Standards Creation Committees
a) International Standards Organization (ISO): product: quality, safety
b) International Telecommunications Union (ITU): comm’ spectrum
b) International Telecommunications Union (ITU): comm’ spectrum
c) American National Standards Institute (ANSI): standards
d) Institute of Electrical and Electronics Engineers (IEEE): promote
technology, education, innovation
e) Electronic Industries Association (EIA): protection to envronment, health
f) Internet Engineering Task Force (IETF): standards for TCP/IP

OSI Model
 OSI: Open Systems Interconnection
 Established in 1947, International Standards
Organization (ISO) is a multinational body
Organization (ISO) is a multinational body
dedicated to worldwide agreement on international
standards.
 An ISO standard that covers all aspects of network
communications is the OSI model. It was first
introduced in the late 1970s.

OSI Model: Layers
 Application Layer
 Presentation Layer
 Session Layer
 Transport Layer
 Network Layer
 Data Link Layer
 Physical Layer

The interaction between layers in the OSI model

7 Application
6 Presentation
5 Session
4 Transport
OSI REFERENCE MODEL
1. Physical Layer
1. Movements of individual bits
2. Physical characteristics of interface, medium
3. Representation of bits
4. Data rate
5. Synchronization of bits
4 Transport
1 Physical
2 Data Link
3 Network
6. Line configuration
7. Topology
8. Transmission mode

Physical Layer
Responsibilities
1. Movements of individual
bits
2. Physical characteristics of
interface, medium
4. Data rate
6. Line configuration
7. Topology
8. Transmission mode

Duties of the Physical layer
 Responsible for movements of individual bits from one hop
(node) to the next
 Physical characteristics of interfaces and media
 It defines the characteristic of the interface between devices and media. It also define
the type of transmission media
 Representation of bits
 Representation of bits
 The bit stream must be encoded into signals. It defines the type of representation ( how
0, 1 are changed to signal).
 Data rate
 It defines the number of bits sent per second and also the duration of bits
 Synchronization of bits
 The sender and receiver must be use the same bit rate also the receiver clock must be synchronized

Duties of the Physical layer
 Line configuration
 Physical layer is concerned with the connection of devices to the media (
point-to point or multipoint)
 Physical topology
How devices connected to make a network
 How devices connected to make a network
 Devices can connected by using Star, mesh , bus, ring or hybrid topology
 Transmission mode
 It defines the direction of transmission between two devices (simplex,
half-duplex, or full duplex)

7 Application
6 Presentation
5 Session
4 Transport
OSI REFERENCE MODEL
2. Data Link Layer
a) Frames
b) Physical addressing (MAC)
c) Flow control
d) Error control
e) Access control
•Error detection and correction methods
4 Transport
1 Physical
2 Data Link
3 Network
•Error detection and correction methods
•IEEE LAN standards
• Bridges
• Switches

Data Link Layer
 Flow control

DLL: Flow Control : Stop and Wait

7 Application
6 Presentation
5 Session
4 Transport
OSI REFERENCE MODEL
3. Network Layer
a)Logical Addressing
b)Routing packets from source to destination.
• Internetworking
• Routing algorithms
• Internet Protocol (IP) addressing
• Routers
4 Transport
1 Physical
2 Data Link
3 Network

Source-to-Destination delivery

7 Application
6 Presentation
5 Session
4 Transport
OSI REFERENCE MODEL
4.Transport Layer
a)Port Address
b)Segmentation and Reassembly
c)Connection control
d)Flow control
e)Error control
• Provides additional Quality of Service.
4 Transport
1 Physical
2 Data Link
3 Network
• Provides additional Quality of Service.
•TCP, UDP

Connection Oriented Service
Connectionless Service

7 Application
6 Presentation
5 Session
4 Transport
OSI REFERENCE MODEL
5.Session Layer
a)Allows users on different machines to establish sessions between them.
b)dialogue control.
c) Token management.
d) Synchronization.
4 Transport
1 Physical
2 Data Link
3 Network

7 Application
6 Presentation
5 Session
4 Transport
OSI REFERENCE MODEL
6. Presentation Layer
a) Concerned with the syntax and semantics of the
information (Translation)
b) Data compression.
c) Data encryption.
4 Transport
1 Physical
2 Data Link
3 Network
c) Data encryption.

7 Application
6 Presentation
5 Session
4 Transport
OSI REFERENCE MODEL
7. Application Layer
a) Provides protocols that are commonly needed.
Main topics:
• File Transfer Protocol (FTP)
• HyperText Transfer Protocol (HTTP)
• Simple Mail Transfer Protocol (SMTP)
• Simple Network Management Protocol (SNMP)
4 Transport
1 Physical
2 Data Link
3 Network
• Simple Network Management Protocol (SNMP)
• Network File System (NFS)
• Telnet

OSI Model: Summary
Image is copied from Forouzan

TCP / IP Protocol Suite
 TCP: Transmission Control Protocol
 IP : Internet Protocol

HTTP

ARP
Address Resolution Protocol (ARP) is a communication
protocol used for discovering MAC address, associated
with a given IP address.
Map a logical Address to a physical Address
An ARP request is broadcast; an ARP reply is unicast.

RARP
Reverse Address Resolution Protocol:
Map a Physical Address to a logical Address
RARP request packets are broadcast;RARP reply packets are unicast.

IP Protocol
IP Protocol
•
•IP provides unreliable and connectionless
IP provides unreliable and connectionless
datagram delivery.
datagram delivery.
•
•IP protocol has no error
IP protocol has no error-
-reporting or error
reporting or error-
-
correcting mechanism.
•
•Logical Address in TCP/IP are called IP Address
Logical Address in TCP/IP are called IP Address

 ICMP: Internet Control Message Protocol
 used by network devices (routers etc.,) to send error messages.
 IGMP: Internet Group Management Protocol
 is a communications protocol used by hosts and adjacent routers
on IPv4 networks to establish multicast group memberships
 provides Connection oriented service such as reliable, ordered,
and error-checked delivery of data.
 UDP: User Datagram Protocol
 uses a connectionless communication where error checking and
correction are not necessary. Used for time-sensitive applications.

 SMTP: Simple mail transfer protocol
 is an Internet standard for electronic mail (email)
transmission
 HTTP: Hyper Text Transfer Protocol
 is an application protocol and forms foundation for
 is an application protocol and forms foundation for
data communication using World Wide Web(www)
 FTP: File Transfer Protocol
 is a standard network protocol used for transfer of
computer files between a client and server on a
computer network

 DNS: Domain Name System
 hierarchical decentralized naming system, responsible for assigning
domain names and mapping those names to Internet resources
(Phonebook of Internet)
 SNMP: Simple Network Management Protocol
 used for collecting and organizing information about managed devices
on IP networks. Monitor and manage network devices over an IP.
on IP networks. Monitor and manage network devices over an IP.
 RPC: remote procedure call
 Computer program can execute a procedure in a different address
space. Used to communicate bw processes on different workstations.
 POP: Post Office Protocol
 used by e-mail clients to retrieve e-mail from a server in an IP network

Example : physical addresses
Data
87 10
1
packet
discarded
2
packet
discarded
3
packet
accepted
Data
87 10
4

logical addresses
Data
A P
20 10 Data
A P
20 10
Physical
addresses
changed
Data
A P
33 99
69
changed
Data
A P
33 99
Physical
addresses
changed
Data
A P
95 66 Data
A P
95 66

A Sender Receiver P
port numbers
Data Data
Internet
a Data
j
A P
H2
a Data
j
A P
a Data
j
Data
a Data
j
A P
H2
a Data
j
A P
a Data
j
Data

DCCN Unit 1.pdf

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