midterm review - network layers. computer 1computer 2 2
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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]