Assessment 1 Review Network Layers

Computer 1 Computer 2

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Application Layer (Chapter 2)

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Application Layer

Network Layer

Transport Layer

Applications(e.g., email, web, word processing)

• The software that enables the user to perform useful work

• Application architecture• The way in which the functions of the application layer software are

spread among the clients and servers on the network

• Functions of Application Layer

2.1 Application Architecture

Splitting the work across the client and the server

Basic Software Components:• Presentation Logic

• Application Logic

• Data Access Logic

• Data

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2.2 Various Architectures

Host-Based

Client-Based

Client-Server Based• Thin Client/Thick Client

Multi-Tier Architectures

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2.3 Sending HTTP Request & Email

Web Transmission• 2-Tier network – Client/Server• Thin Client• HTTP Request, HTTP Response

Email Transmission• 2-Tier network – Client Server• Thick and Thin Clients• SMTP, POP, IMAP

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Network Layers

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Computer 1 Computer 2

Data Link Layer (Chapter 4)

Responsible for moving messages from one device to another

Controls the way messages are sent on media

Organizes physical layer bit streams into coherent messages for the network layer

Major functions of a data link layer protocol Media Access Control

Error Control

Message Delineation

Data Link Layer

Physical Layer

Network Layer

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4.1 Media Access Control (MAC)

Controlling when and what computer transmit Why used When to use

Two possible approaches Controlled access Contention based access

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4.2 Major Functions of Error Control

• Error prevention

• Error detection (how do these work, which is better?)• Parity checks (Even and Odd)• Cyclic Redundancy Check (CRC)

• Error correction• Retransmission

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4.3 Automatic Repeat reQuest (ARQ)

Process of requesting a data transmission be resent

Main ARQ protocols

Stop and Wait ARQ (A half duplex technique) Continuous ARQ (A full duplex technique) Flow Control

• Window

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4.4 Data Link Protocols

Classification Asynchronous transmission Synchronous transmission

Differ by Message delineation Frame length Frame field structure

frame k frame k+1frame k-1

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Network Layers

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Computer 1 Computer 2

Physical Layer (Chapter 3)

Includes network hardware and circuits

Types of Circuits Physical circuits connect devices & include actual

wires

Logical circuits refer to the transmission characteristics of the circuit

Physical and logical circuits may be the same or different. For example, in multiplexing, one physical wire may carry several logical circuits.

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Physical Layer

Network Layer

Data Link Layer

3.1 Circuits

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Physical connection (wire)

Configuration types (physical layout of the circuit):

Point-to-Point Configuration

Multipoint Configuration

3.1.2 Data Flow (Transmission)

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How does data flow through the circuit (circuits can be designed to permit data flow)

Configuration types:

Simplex

Half-Duplex

Full-Duplex

3.1.3 Multiplexing

Breaking up a higher speed circuit into several slower (logical) circuits Several devices can use it at the same time Requires two multiplexer: one to combine;

one to separate

Main advantage: cost Fewer network circuits needed

Categories of multiplexing: Frequency division multiplexing (FDM) Time division multiplexing (TDM) Inverse Multiplexing

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3.2 Media – Guided Media

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Physical matter that carries the transmission

Types:

• Guided Media• Radiated (Unguided) Media

http://whatis.techtarget.com/definition/0,,sid9_gci214198,00.htmlhttp://www.iupui.edu/~ilight/index.html

3.2 Media Summary

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3.3 Transmission of Data

Computers produce binary data (0 or 1) (i.e. discrete, predictable values)

Standards needed to ensure both sender and receiver understands this data Codes Signals

Digital• Bipolar, Unipolar

Analog• Frequency, Amplitude, Phase

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3.3 Transmission Modes

Bits in a message can be sent on: a single wire one after another (Serial transmission) multiple wires simultaneously (Parallel transmission)

Two Modes of transmission:

• Serial Mode

• Parallel Mode

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