01-computer networks

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Computer Networks


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Introduction Computer Network 2

A History Lesson of Networking

1969 ARPANET, first packet switchednetwork consist of UCLA, Stanford, UC Santa

Barbara and Utah University 1971 first email program

1974 TCP/IP

1980s Local Area Networks (LANs)

1984 OSI Layer

1990s WWW / Internetworking


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Why Networking?

Efficiency and Productivity

Reliability Distributed Systems


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What Applications?

Client/Server Business Applications

Electronic Messaging Information Retrieval


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Network Classification by Area

Wide Area Network

Metropolitan Area Network Local Area Network

Personal Area Network

Ad Hoc Network


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Protocols

Driving Force: need for different proprietarynetworking system to communicate

Protocol: set of rules for acceptable behaviour (howcommunication should take place in)

Specifically: the set of rules used by communicating parties for that

communication to be successful

Suite of protocols cover all required behaviour

Mostly implemented in Software

Complexity demands that protocols are layered


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Advantages of Layering Protocols

Dividing complex network operation into more

manageable layers

Defining the standard interface for the plug-

and-play multi-vendor integration

Facilitate Modular Engineering

Simplifies Teaching and Learning


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ISO/OSI Reference Model

ISO in1984

Open Systems Interconnect (OSI)

A designguideline fornetwork layering

Abstract layers provide different services

Defines 7 layers of service

Each layer provides service to adjacent layers Each layer communicates with same layer in

remote machine


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OSI Reference Model

Physical LayerLink Layer

Network Layer

Transport Layer

Session Layer

Presentation Layer

Application Layer

Physical LayerLink Layer

Network Layer

Transport Layer

Session Layer

Presentation Layer

Application Layer


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Layer1- Physical

Physical Layer:

Move bits between devices

Specifies voltage, wire speed, and pin out cables

Passes data up to data link layer (and receives

from data link layer)


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Layer 2 Data Link

Data Link Layer:

Performs framing of bits, flow and error control but

not correction

Responsible for transmission of frames across the

physical link

Provide access to media using MAC address

Passes data between physical and network layers


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The Institute of Electrical and Electronics Engineers (IEEE)

has subdivided the data link layer into two sublayers: Logical

Link Control (LLC) and Media Access Control (MAC).


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The Logical Link Control (LLC) 802.2 sublayer is responsiblefor identifying Network Layer protocols and thenencapsulating them. An LLC header tell the Data Link Layer

what to do with the packet if a frame is coming. Also provideflow control and sequencing of control bits

The Media Access Control (MAC) sublayer of the data linklayer manages protocol access (logical topologies) to thephysical network medium. The IEEE MAC specification

defines MAC addresses, which enable multiple devices touniquely identify one another at the data link layer. IEEE802.3 dan802.5


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Layer 3 - Network Network Layer:

Passes data between data link and transport

layers Responsible for routing data across a network,

from source to destination usingnetwork-wide

addressing

Pass data between (separate) subnetworks Hides network topology from higher layers


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Layer4- Transport

Transport Layer:

Passes data betweennetwork and session layers

Provides reliable end-to-end delivery of data,

including flow and error control of packets

Fragmentation of large messages

Quality of Service (QoS), usually with layer 3 Last of the pure network layers


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Layer 5 - Session

Session Layer:

Passes data between presentation and transport

layers

Responsible for managingnetwork sessions

(series of related data streams)

Provides synchronization and scheduling


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Layer6- Presentation

Presentation Layer:

Passes data between application and session

layers

Provides translation services for data to ensure

applications are using compatible formats

E.g. converting from ASCII to EBCDIC text

representations


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Layer7-Application

Application Layer:

Passes data to presentation layer (and receives

from presentation layer)

to and from the user!

Communicates with remote applications

Determines the user capability within the network


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Data Encapsulation


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Data Encapsulation


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OSI Layer vs. TCP/IP Layer


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IP

TCP UDP

FTP File Transfer Protocol

HTTP Hypertext Transfer Protocol

WAP Wireless Application ProtocolSMTP Simple Mail Transfer Protocol

e.g. IEEE 802.x1-2

4

5-7

3


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Some Protocols in TCP/IP Suite


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Quiz

Protocols

What are they?

Why do we layer protocols?

ISO/OSI 7 layer reference model

How does the OSI abstract services?

How does data pass between layers(local/remote)?

How does Internet stack relate to OSI?

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