Midterm 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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Computer 1 Computer 2

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Transport layer (Chapter 5)

Responsible for end-to-end delivery of messages

Responsible for segmentation and reassembly Breaking the message into several smaller

pieces at the sending end Reconstructing the original message into a single whole

at the receiving end

Interacts with Application Layer

Transport Layer

Application Layer

Network Layer

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Transmission Control Protocol (TCP)

• Links the application layer to the network layer• Performs packetization and reassembly • Ensures reliable delivery of packets

TCP Header

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How many bytes does the TCP header add to a message?

24 bytes (if option used) or 20 bytes w/out option

Packetization and Reassembly

receiver

TCP

IP

FTP

TCP

IP

FTP

sender

Application layer sees message as a single block of data

TCP packetization

Delivers incoming packets as they arrive (e.g., Web pages) or to wait until entire message arrives (e.g., e-mail)

TCP reassembly

What size packet to use?

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Done through negotiations

5.2.2 Linking to Application Layer

TCP may serve several Application Layer protocols at the same time Problem Solution

How do we know what number the server uses?

What would be the other type of number used and why?

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TCP

HTTP FTP SMTP …

80 21 25

Standards

Non- Standard Port requiring further configuration (provides greater security

5.2.3 Session Management

A session can be thought of as a conversation between two computers.

Types of Session Management

• Connection Oriented• What is connection oriented? How does it work?• What protocols use connection oriented?• Why?

• Connectionless Routing• What protocols use connectionless?• Why?

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Computer 1 Computer 2

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Network Layer (Chapter 5)

Responsible for addressing and routing of messages Selects best path from computer to computer

until the message reaches destination

Performs encapsulation on sending end Adds network layer header to

message segments

Performs decapsulation on receiving end Removes the network layer header at receiving end and

passes them up to the transport layer

Network Layer

Transport Layer

Data Link Layer

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IP Packet Formats: IPv4 (24 bytes) vs. IPv6 (40 bytes)

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IPv4

IPv6

5.1 Types of Addresses

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• Application Layer Address• Assignment

• How do we get the URL’s IP address?• How do this work?

• Address Resolution

• Network Layer Address• Assignment (Subnets)

• What is sent out to assign IP Address?

• Data Link Layer Address• Assignment

• What is sent out if MAC Address is unknown?

Network Layer

Data Link Layer

Application Layer

Transport Layer

5.2 Routing

Process of identifying what path to have a packet take through a network from sender to receiver

Routing Tables Used to make routing decisions Shows which path to send packets on

to reach a given destination Kept by computers making routing decisions

Routers Special purpose devices used to handle routing decisions

on the Internet Maintain their own routing tables

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Dest.

B

C

D

E

F

G

Next

B

B

D

D

D

B

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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Overall Efficiency of Transmissions

You want to transmit a 500 byte email message. What would be the efficiency in transmitting this message?

Overhead:• SMTP:• TCP:• IP: • Ethernet:

What about an HTTP file of 4000 bytes?

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24 bytes

24 bytes

34 bytes

100 bytes (could be variable)

EFF = 500/(500+100+24+24+34) = 73%

EFF = [# of data bytes]/ [#data bytes + # of overhead]