Computer Network Complete Introduction

Computer Networks 06.01.2016- 1
Computer Engineering and Applications
CSE4003: CN
Computer Networks:
Introduction
Dr. Manas Kumar Mishra
manas.mishra@gla.ac.in

CSE4003 Computer Networks: Course Overview
UNIT I
Introduction Concepts: Goals and Applications of Networks, Network structure and
architecture, The OSI reference model, services, Network Topology Design, connecting
devices,
Physical Layer: Transmission Media, Line coding scheme, Basic idea of modulation and
multiplexing, Switching methods.
Medium Access sub layer: Medium Access sub layer - Channel Allocations, LAN protocols -
ALOHA protocols, CSMA, CSMA/CD, Overview of IEEE standards
UNIT II
Data Link Layer: HDLC and point to point protocol, Error detection and correction, Flow
control (sliding window protocol)
Network Layer: Network Layer –IP addressing, Internetworking, Address mapping,
introduction to IPv6, transition from IPv4 to IPv6, routing.
UNIT III
Transport Layer: Transport Layer - Design issues, connection management, Flow control, TCP
window management, congestion control-slow start algorithm
Session Layer: Design issues, remote procedure call.
Presentation Layer: Design issues, Data compression techniques, cryptography
Application Layer: Application Layer: File Transfer, Access and Management, Electronic mail,
Virtual Terminals

Literature I
This is a good textbook for
introductory courses to
networking.
The chapters include
detailed yet easy to grasp
explanations of the topics
covered, often with figures
and demonstrations.

Literature II
This is a good book both as
an introduction to networking
and as a reference for
graduate coursework.
Good end-of-chapter
questions, with text depth
appropriate for a smart child
or an average 2nd year CS
undergrad.

Literature III
This is a book with an early
emphasis on application-layer
paradigms and application
programming interfaces (the
top layer), encouraging a
hands-on experience with
protocols and networking
concepts, before working
down the protocol stack to
more abstract layers.

Literature IV
The book takes a structured
approach to explaining how
networks work from the inside out.
It starts with an explanation of the
physical layer of networking,
computer hardware and
transmission systems; then works its
way up to network applications.
It presents key principles, then
illustrates them utilizing real-world
example networks that run through
the entire book.

Literature V
This new networking text
follows a top-down approach.
The presentation begins with
an explanation of the
application layer, which makes
it easier for students to
understand how network
devices work, and then, with
the students fully engaged, the
authors move on to discuss
the other layers, ending with
the physical layer.

Computer Networks
A network consists of two or more computers that are linked in order to share
resources (such as printers and CDs), exchange files, or allow electronic
communications.
The computers on a network may be linked through cables, telephone lines, radio
waves, satellites etc.
A popular example of a computer network is the Internet, which allows millions of
users to share information.

1st goal: Resource Sharing
The goal is to make all programs, equipment, and especially data available to anyone
on the network without regard to the physical location of the resource and the user.
Equipment:
Printers, Scanner, CD-Burners…
Information:
Customer records, Product information ,inventories, financial statements, tax
information

2nd goal: A Computer network to do
with people
A second goal of setting up a computer network has to do with people rather than
information or even computers. A computer network can provide a powerful
communication medium among employees.
Email
Cooperate with other to work
VoIP
Videoconferencing

3rd goal: e-Commerce
A third goal for many companies is doing business electronically with other
companies, especially suppliers and customers.
e-Commerce
B2B: Manufacturers and its suppliers.
B2C: companies and its customers.

Advantages of Computer Networks
File Sharing: Networks offer a quick and easy way to share files directly.
Resource Sharing: All computers in the network can share resources such as printers,
fax machines, modems and scanners.
Communication: Those on the network can communicate with each other via e-mail,
instant messages etc.
Flexible Access: Networks allow their users to access files from computers
throughout the network.
Sharing of Information: Computer networks enable us to share data and information
with the computers that are located geographically large distance apart.

Evolution of computer networks

Network Technologies
Classification Based on Transmission Technology
Broadcast networks
Broadcast network have a single
communication channel that is shared by
all the machines on the network
Point-to-point networks
There may exist multiple paths between a
source-destination pair and the switching nodes are
to provide a switching facility that will move data from
node to node until they reach the destination.

Network Technologies
Classification Based on Scale
Local Area Network (LAN)
Metropolitan Area Network (MAN)
Wide Area Networks (WAN)

LAN is usually privately owned and links the devices in a single office, building or
campus of up to few kilometers in size.
LANs are distinguished from other kinds of networks by three categories: their size,
transmission technology and topology.
LANs are restricted in size
which means that their worst-case transmission time is bounded and known in
advance. Hence is more reliable as compared to MAN and WAN. Knowing this
bound makes it possible to use certain kinds of design that would not otherwise be
possible. It also simplifies network management.
LAN typically uses transmission technology consisting of single cable to which all
machines are connected.
Traditional LANs run at speeds of 10 to 100 Mbps (but now much higher speeds
can be achieved).
The most common LAN topologies are bus, ring and star.

Metropolitan Area Networks (MAN)
MAN is designed to extend over the entire city.
It may be a single network as a cable TV network or it may be means of connecting a
number of LANs into a larger network so that resources may be shared.
MAN is wholly owned and operated by a private company or may be a service
provided by a public company.
The main reason for distinguishing MANs as a special category is that a standard has
been adopted for them. It is DQDB (Distributed Queue Dual Bus) or IEEE 802.6.

Metropolitan Area Networks (MAN)

Wide Area Network (WAN)
WAN provides long-distance transmission of data, voice, image and information over
large geographical areas that may comprise a country, continent or even the whole
world.
WANs may utilize public, leased or private communication devices, usually in
combinations, and can therefore span an unlimited number of miles.
A WAN that is wholly owned and used by a single company is often referred to as
enterprise network.

Wide Area Network (WAN)

Internet – network of networks
Internet is a collection of networks or network of networks.
The basic difference between WAN and Internet is that WAN is owned by a single
organization while internet is not so.

Personal Area Network (PAN)
PAN is a computer network used for communication among computer
devices, including telephones and personal digital assistants, in proximity to
an individual's body.
 The devices may or may not belong to the person in question.
The reach of a PAN is typically a few meters.

Personal Area Network (PAN)

Classification by scale

Network Computing Models
Centralized Computing
(Client-Server Network)
A client-server network is where every client is connected to the server .
Server or mainframe computer has huge storage and processing capabilities.

Network Computing Models
Distributed Computing
(Peer-to-Peer Network)
All devices have same power.
It interconnects one or more computers.
Centralized backup is not possible.

Simultaneous Access
 Shared Peripheral Devices
 Personal Communication
 Easier Backup
Uses of Computer Network

Home Applications
Access to remote information
Web
Person-to-person communication
Email, VoIP
e-commerce
Interactive entertainment
IPTV, Gaming E-mail
P2P - Peer to Peer
Other applications
Ubiquitous computing
IoT ( Internet of Things)
Sensor Networks
RFID (Radio Frequency IDentification)
Mobile Users
SoLoMo
Applications of networks

Every Network Includes:
1.At least two computers that have something to share.
1.A cable or wireless pathway, called Transmission Media, for computers to signal each
other.
1.Rules, called Protocols, so that computers can use the unified principle of data
communication.
1.Networking Interface Cards (NIC)

Protocol Stack
Why Layered architecture?
1.To make the design process easy by breaking unmanageable tasks into several
smaller and manageable tasks (by divide-and-conquer approach).
1.Modularity and clear interfaces, so as to provide comparability between the
different providers' components.
1.Ensure independence of layers, so that implementation of each layer can be changed
or modified without affecting other layers.
1.Each layer can be analyzed and tested independently of all other layers.

Open System Interconnection (OSI)
Reference Model
Developed by International Organization for Standardization (ISO) in 1984

Terminologies
A protocol
is a formal set of rules and conventions that governs how computers exchange
information over a network medium.
the service user, the service provider, and the service access point (SAP)

Interaction between OSI Model Layers

Analogy of Protocol Hierarchies:
The philosopher-translator-secretary architecture

Virtual Communication: Sino-US Talk

OSI Layers

Terminologies
Header:
Upper layer puts a header in front of the message to identify the message and
passes the result to lower layer
The header includes control information such as sequence numbers to keep the
right order.
Size of messages
There is always a limit to the size of messages imposed by certain layer protocol.
So incoming messages must be broken into smaller units (packets) in this layer.

Information Flow

Example: Path of a Web page request &
Encapsulation

An Exchange Using the OSI Model

Physical Layer

Physical Layer
Purpose
Transmits raw bits across a medium.
Concerns are
Voltage: how many volts for 1 / 0
Timing: how many ns a bit lasts
Duplexing: transmission in both directions?
Connectors: how many pins? What is each pin?
etc.

Data Link Layer

Data Link Layer
Purpose:
Transform a raw transmission line into a line that appears free of undetected
transmission errors to the networks layer
Concerns:
Framing - Breaks apart input data into frames and transmit the frames
sequentially.
Error handling – if the service is reliable, the receiver confirms correct receipt of
each frame by sending back an acknowledgement frame.
Flow control - keeps a fast transmitter from drowning a slow receiver in data.
Medium Access Control – how to control access to the shared channel for
broadcast networks.

Data Link Layer Example

Network Layer

Network Layer
Purpose
Route packets from source to destination
Concerns
Routing - What path is followed by packets from source to destination. Can be
based on a static table, can be determined when the connection is created, or can
be highly dynamic, being determined anew for each packet, to reflect the current
network load.
Congestion - Controls the number packets in the subnet.
QoS – Quality of Service provided (delay, transit time, jitter…)
Heterogeneity - Interfacing so that one type of network can talk to another.
Addressing, packet size, protocols…

12 Jan

Transport Layer

Transport Layer
Purpose
Accept data from above it, split it up into smaller units if need be, pass them to
network layer, and ensure that the pieces all arrive correctly at the other end.
Concerns
Service Decisions - What type of service to provide; error-free point to point,
datagram, etc.
End-to-end: it carries data all the way from the source to the destination.
Reliability - Ensures that packets arrive at their destination. Reassembles out of
order messages.
Hides network - Allows details of the network to be hidden from higher level
layers.
Mapping - Determines which messages belong to which connections.
Flow control - keeps a fast transmitter from flooding a slow receiver.

Session Layer

Session Layer
Purpose
Allow users on different machines to establish sessions between them
Concerns
Dialog control - keep track of whose turn it is to transmit
Token Management – prevent two parties from attempting the same critical
operation at the same time
Synchronization – checkpointing long transmissions to allow them to pick up
from where they left off in the event of a crash and subsequent recovery.

Presentation Layer

Presentation Layer
Purpose
Make it possible for computers with different data representations to
communicate
Concerns
Syntax and semantics of information transmitted.
Understands the nature of the data being transmitted. Converts ASCII/EBCDIC,
big endian/little endian

Application Layer

Application Layer
contains a variety of protocols that are commonly needed by users.
HTTP
FTP
SMTP

The TCP/IP Reference Models
Link layer
Internet layer
Transport layer
Application layer
the key
a packet-switching network based on a connectionless layer that runs across different networks.

The TCP/IP Reference Models

Comparing OSI and TCP/IP Models
Concepts central to the OSI model
Services
Interfaces
Protocols
OSI has good definition of service, interface, and protocol as discussed before. Fits
well with object oriented programming concepts. Protocols are better hidden.
The TCP/IP model did not originally distinguish between service, interface, and
protocol.
With TCP/IP, the protocols came first; model was just a description of the protocols.
But then the model isn't good for any other protocols.

Different philosophy
Which is first?
Reference Model
vs
Corresponding
protocols
Specific differences
Number of layers: 7 vs. 4
Connectionless vs. connection-oriented
OSI supports both in the network layer, but only Connection-oriented
communication in the transport layer
TCP/IP supports only connectionless mode in the network layer but supports
both in the transport layer, giving the users a choice.

What is a Topology?
Network topologies describe the ways in which the elements of a network are
mapped. They describe the physical and logical arrangement of the network nodes.
The physical topology of a network refers to the configuration of cables, computers,
and other peripherals

Different Types of Topologies
Bus Topology
Star Topology
Ring Topology
Mesh Topology
Tree Topology
Hybrid Topology

Bus Topology
All the nodes (file server, workstations, and peripherals) on a bus topology are
connected by one single cable.
A bus topology consists of a main run of cable with a terminator at each end. All
nodes (file server, workstations, and peripherals) are connected to the linear cable.
Popular on LANs because they are inexpensive and easy to install.

Bus Topology

Bus Topology
Advantages of Bus Topology
It is Cheap, easy to handle and implement.
Require less cable
It is best suited for small networks.
Disadvantages of Bus Topology
The cable length is limited. This limits the number of stations that can be connected.
This network topology can perform well only for a limited number of nodes.


Ring Topology
In a ring network, every device has exactly two neighbours for communication
purposes.
All messages travel through a ring in the same direction.
A failure in any cable or device breaks the loop and can take down the entire
network.
 To implement a ring network we use the Token Ring technology
A token, or small data packet, is continuously passed around the network. When a
device needs to transmit, it reserves the token for the next trip around, then attaches
its data packet to it.

Ring Topology

Ring Topology
Advantage of Ring Topology
Very orderly network where every device has access to the token and the
opportunity to transmit.
Easier to Manage than a Bus Network
Good Communication over long distances
Handles high volume of traffic
Disadvantages of Ring Topology
The failure of a single node of the network can cause the entire network to fail.
The movement or changes made to network nodes affects the performance of the
entire network.

Star Topology
In a star network, each node (file server, workstations, and peripherals) is connected
to a central device called a hub.
The hub takes a signal that comes from any node and passes it along to all the other
nodes in the network.
Data on a star network passes through the hub, switch, or concentrator before
continuing to its destination.
The hub, switch, or concentrator manages and controls all functions of the network.
The star topology reduces the chance of network failure by connecting all of the
systems to a central node.

Star Topology

Star Topology
Advantages of Star Topology
Easy to manage
Easy to locate problems (cable/workstations)
Easier to expand than a bus or ring topology.
Easy to install and wire.
Easy to detect faults and to remove parts.
Disadvantages of Star Topology
Requires more cable length than a linear topology.
If the hub or concentrator fails, nodes attached are disabled.
More expensive because of the cost of the concentrators.

Tree Topology
A tree topology (hierarchical topology) can be viewed as a collection of star
networks arranged in a hierarchy.
 This tree has individual peripheral nodes which are required to transmit to and
receive from one other only and are not required to act as repeaters or regenerators.
The tree topology arranges links and nodes into distinct hierarchies in order to allow
greater control and easier troubleshooting.
This is particularly helpful for colleges, universities and schools so that each of the
connect to the big network in some way.

Tree Topology

Tree Topology
Advantages of a Tree Topology
Point-to-point wiring for individual segments.
Supported by several hardware and software vendors.
All the computers have access to the larger and their immediate networks.
Disadvantages of a Tree Topology
Overall length of each segment is limited by the type of cabling used.
If the backbone line breaks, the entire segment goes down.
More difficult to configure and wire than other topologies.

Mesh Topology
In this topology, each node is connected to every other node in the network.
Implementing the mesh topology is expensive and difficult.
In this type of network, each node may send message to destination through
multiple paths.
While the data is travelling on the Mesh Network it is automatically configured to
reach the destination by taking the shortest route which means the least number of
hops.

Mesh Topology

Mesh Topology
Advantage of Mesh Topology
No traffic problem as there are dedicated links.
It has multiple links, so if one route is blocked then other routes can be used for data
communication.
Points to point links make fault identification easy.

Disadvantage of Mesh Topology
There is mesh of wiring which can be difficult to manage.
Installation is complex as each node is connected to every node.
Cabling cost is high.

Hybrid Topology
A combination of any two or more network topologies.
A hybrid topology always accrues when two different basic network topologies are
connected.
It is a mixture of above mentioned topologies. Usually, a central computer is
attached with sub-controllers which in turn participate in a variety of topologies

Hybrid Topology

Hybrid Topology
Advantages of a Hybrid Topology
It is extremely flexible.
It is very reliable.
Disadvantages of a Hybrid Topology
Expensive

Networking hardware includes all computers, peripherals, interface
cards and other equipment needed to perform data-processing and
communications within the network.
What is Networking Hardware?

Networking Hardware
Network Interface Card
Hub
Repeater
Bridge
Switch
Gateway

Network Interface Cards
Network interface cards, commonly referred to as NICs, are used to connect a PC to
a network.
 The NIC provides a physical connection between the networking cable and the
computer's internal bus.
Different computers have different bus architectures; PCI bus master slots are most
commonly found on 486/Pentium PCs and ISA expansion slots are commonly found
on 386 and older PCs.
NICs come in three basic varieties: 8-bit, 16-bit, and 32-bit. The larger the number
of bits that can be transferred to the NIC, the faster the NIC can transfer data to the
network cable.

Network Interface Cards

Hubs
A hub joins multiple computers (or other network devices) together to form a
single network.
On this network, all computers can communicate directly with each other.
The networking hub is a junction box with several ports in the back for receiving
the Ethernet cables that are plugged into each computer on the LAN.

Types of Hubs
A passive hub serves simply as a passage for the data, enabling it to go from one
device to another.
Intelligent hub include additional features that enables an administrator to
monitor the traffic passing through the hub and to configure each port in the hub.
Switching hub, actually reads the destination address of each packet and then
forwards the packet to the correct port.

Hubs

Repeater
Since a signal loses strength as it passes along a cable, it is often necessary to boost
the signal with a device called a repeater.
A repeater is an electronic device that receives a signal, cleans it of unnecessary
noise, regenerates it, and retransmits it at a higher power level so that the signal can
cover longer distances without degradation.
A good example of the use of repeaters would be in a local area network using a
star topology with unshielded twisted-pair cabling.

Repeaters

Switch
A network switch is a small hardware device that joins multiple computers
together within one local area network (LAN).
Network switches appear nearly identical to network hubs, but a switch generally
contains more intelligence than a hub.
Unlike hubs, network switches are capable of inspecting data packets as they are
received, determining the source and destination device of each packet, and
forwarding them appropriately.
Allow several users to send information over a network at the same time without
slowing each other down.

Switch

Router
A device to interconnect SIMILAR networks, e.g. similar protocols and workstations
and servers.
A router is an electronic device that interconnects two or more computer
networks, and selectively interchanges packets of data between them.
Each data packet contains address information that a router can use to determine
if the source and destination are on the same network, or if the data packet must be
transferred from one network to another.

Router

Bridge
A bridge is a device that connects a local area network (LAN) to another local area
network that uses the same protocol (for example, Ethernet or token ring).
The function of a bridge is to connect separate networks together. Bridges connect
different networks types (such as Ethernet and Fast Ethernet) or networks of the
same type.
Bridges map the Ethernet addresses of the nodes residing on each network
segment and allow only necessary traffic to pass through the bridge. When a packet
is received by the bridge, the bridge determines the destination and source
segments.

Types of Bridges
Bridges come in three basic types:
Local bridges: Directly connect local area networks (LANs)
Remote bridges: Can be used to create a wide area network (WAN) link between
LANs. Remote bridges have been replaced with routers.
Wireless bridges: Can be used to join LANs or connect remote stations to LANs.

Bridges

Gateway
Gateways are used to interconnect two different networks having different
protocols.
Networks using different protocols use different addressing formats.
A gateway is a network point that acts as an entrance to another network.
Gateways are also called protocol converters.

Gateway

What is the difference?
Bridge: device to interconnect two LANs that use the SAME logical link control
protocol but may use different medium access control protocols.
Router: device to interconnect SIMILAR networks, e.g. similar protocols and
workstations and servers.
Gateway: device to interconnect DISSIMILAR protocols and servers, and Macintosh
and IBM LANs and equipment

Computer Engineering and Applications
Thank you.
Computer Networks
Dr. Manas Kumar Mishra
manas.mishra@gla.ac.in
06.01.2016

Computer Network Complete Introduction

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