DCET CCn 3 Internetworking

8/6/2019 DCET CCn 3 Internetworking

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Why have Computer Networks?

Resource sharing

Communication

Information sharing


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Different Types of Computer

Networks Switched Networks and Broadcast

Networks

Local Area Networks - LANs Metropolitan Area Networks - MANs

Wide Area Networks - WANs


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Switched Networks and

Broadcast Networks In switched networks the message travels

from one node to another on its path from

source to destination. The message onlytravels through the nodes that are

necessary to pass from a given source to

a destination. Example Telephone

Network.

In Broadcast networks the message is

sent to all the nodes on the network.

Example Ethernet Local Area Network.


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Local Area Networks

Small geographical area. Less than 1 km.

A floor or a building.

Owned by a department or anorganization.

Very high speeds and low latency.


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Metropolitan Area Networks

Medium size geographical area. 10 km.

A campus or a city.

Owned by a large organization or a groupof organizations.

High speeds and medium latency.


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Wide Area Networks

Long distances. 100 km.

Owned by very large organizations,

governments, telcos. Low to high speed and high latency.

Two Types Of WAN

Circuit Switching Packet Switching


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Circuit-Switching

Definition: Communication in which a dedicatedcommunications path is established between two

devices through one or more intermediate switching

nodes Oldest Networking Technology - more than a

hundred years old

Dominant in both voice and data communications

today

e.g. PSTN is a circuit-switched network

Relatively inefficient (100% dedication even without

100% utilization)


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Circuit Switching

In circuit switching network any two

stations wishing to communicate first

establish a connection by requesting to the

network.

The network responds by arranging a

connection in such a way that a

dedicated/physical path is establishedbetween the two parties


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Circuit Switching Networks


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Packet Switching

Packet Switching refers to protocols in which

messages are divided into packets before they

are sent. Each packet is then transmitted

individually and can even follow different routesto its destination. Once all the packets forming a

message arrive at the destination, they are

recompiled into the original message.

Examples X.25, and Frame Relay, are based on

packet-switching technologies


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Packet Switching Networks


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What is the Internet?

A world-wide network of networks.

The whole thing started in the late 1960s when the

US Government through its Advanced Research

Project Agency (ARPA) decided to set up contractwork with universities and corporate research

community representatives to interconnect world-

wide computers in a single network.

In 1969 the first internetwork (ARPANET) occurredwith 4 nodes using routing devices that allowed data

packet deliveries between otherwise incompatible

computers.


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OSI Reference Model

Application

Presentation

Session

Transport

Network

Datalink

Physical


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Open Systems Interconnection

(OSI) Reference Model

y The Open Systems Interconnection ( OSI ) reference

model describes how information from a software

application in one computer moves through a network

medium to a software application in another computer.

y The OSI reference model is a conceptual model

composed of seven layers, each specifying particular

network functions.

y The model was developed by the International

Organization for Standardization (ISO) in 1984, and it is

now considered the primary architectural model for

intercomputer communications.


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Protocols

y The OSI model provides a conceptual framework

for communication between computers, but the

model itself is not a method of communication.

Actual communication is made possible by using

communication protocols.

yA protocol is a formal set of rules and conventions

that governs how computers exchange information

over a network medium.

y A protocol implements the functions of one or

more of the OSI layers.


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Headers and data can be

encapsulated during information

exchange.


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Physical Layer

The Physical Layerdescribes the physical

properties of the various communications media,

as well as the electrical properties and

interpretation of the exchanged signals. Ex: thislayer defines the size of Ethernet coaxial cable,

the type of BNC connector used, and the

termination method.

Electrical - Signals specifications and properties,

Electrical Properties (impedance)

Mechanical - Physical Media dimensions,

Connectors


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Datalink Layer

y The data link layer provides

y physical addressing

Physical addressing as opposed to network addressing defines how

devices are addressed at the data link layer.,

y network topology,

Network topology consists of the data-link layer specifications that

often define how devices are to be physically connected, such as in

a bus or a ring topology

y error notification, Error notification alerts upper-layer protocols that a transmission

error has occurred


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sequencing of frames

The sequencing of data frames reorders frames that are

transmitted out of sequence

flow control.

flow control moderates the transmission of data so that the

receiving device is not overwhelmed with more traffic than it can

handle at one time.

The Institute of Electrical and Electronics Engineers (IEEE) hassubdivided the data-link layer into two sublayers: Logical Link

Control (LLC) and Media Access Control (MAC)


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Network Layer

y The network layer provides routing and related

functions that enable multiple data links to be

combined into an internetwork. This is

accomplished by the logical addressing as

opposed to the physical addressing of devices.

y The network layer supports both connection-

oriented and connectionless service from higher-

layer protocols.

y Some Examples include Border Gateway Protocol(BGP); Open Shortest Path First (OSPF); and

Routing Information Protocol (RIP),


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Transport Layer

y The transport layer implements reliable

internetwork data transport services that are

transparent to upper layers.

y

Transport-layer functions typically includey flow control

Flow control manages data transmission between

devices so that the transmitting device does not send

more data than the receiving device can process.


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ymultiplexing,

Multiplexing enables data from several applications tobe transmitted onto a single physical link.

y virtual circuit management,

Virtual circuits are established, maintained, and

terminated by the transport layer.

y error checking and recovery.

Error checking involves creating various mechanisms

for detecting transmission errors, while error recovery

involves taking an action, such as requesting thatdata be retransmitted, to resolve any errors that

occur.


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Basic difference between this layer and lower

layers is that it provides an end-to-end reliable

transfer of data packet

Some examples are Transmission Control

Protocol,(TCP) is the protocol in the TCP/IP suite

that provides reliable transmission of data.

UDP Connectionless protocol


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Session Layer

Establishes, manages, and terminatesconnections (sessions) between applicationprocesses

Gives a session service by tokenmanagement

Responsible for check pointing recovery bysynchronization

The Session Layer provides the means fortwo application layer entities to synchronizeand manage their data exchange.


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y Some examples of session-layer implementations

include Zone Information Protocol (ZIP), the

AppleTalk protocol; and Session Control Protocol

(SCP),


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Presentation Layer

y The presentation layer provides a variety of coding

and conversion functions that are applied to

application layer data.

y . Some examples of presentation-layer coding andconversion schemes include

y common data representation formats,

y conversion of character representation

formats ,such as EBCDIC and ASCII


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y common data compression schemes, ,such as Some well-known standards for video

include QuickTime and Motion (MPEG). For the

graphic image formatsar

e Graphics InterchangeFormat (GIF), Joint Photographic Experts Group

(JPEG), and Tagged Image File Format (TIFF).

y common data encryption schemes.


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Application Layer

y The application layer is the OSI layer closest to the

end user, which means that both the OSI

application layer and the user interact directly with

the software application.

Two key types of application-layer implementations are

y TCP/IP applications

TCP/IP applications are protocols, such as Telnet, File

Transfer Protocol (FTP), and Simple Mail TransferProtocol (SMTP)


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Networking Devices

Hubs, Repeaters, Concentrators

Switches, Bridges

Routers


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Repeaters ,Bridges, Switches

and Routers


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Repeaters

Operate at the Physical Layer

Attempt to forward all Frames

Error Frames will be forwarded

Collision domains are not isolated Broadcast domains are not isolated

A repeater receives and then immediatelyretransmits each bit.

A repeater has no memory and does not dependon any particular protocol. It duplicateseverything, including the collisions.


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Bridges

A bridge is a device which has two or more

ports which can be connected to a variety of

media types, and provides a mechanism for

the filtering and forwarding of data framesamong the ports while building one large

logical network.

Operate at the Data Link Layer

Selectively forwards frames Error Frames will not be forwarded

Collision domains are isolated

Broadcast domains are not isolated


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Routers

Operate at the Network Layer

Selectively forwards frames

Error Frames will not be forwarded Collision domains are isolated

Broadcast domains are isolated

Protocols can be Filtered Has an effect on MAC Addresses but no

effect on Network Addresses

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DCET CCn 3 Internetworking