Download Midterm Review - Network Layers

Midterm Review - Network
Layers
Computer 1
Computer 2
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Application Layer (Chapter 2)
Applications
Application Layer
(e.g., email, web,
word processing)
Transport Layer
Network Layer
•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
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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
Application Layer
Responsible for segmentation and
reassembly
Transport Layer
 Breaking the message into several smaller
Network Layer
pieces at the sending end
 Reconstructing the original message into a single whole at the
receiving end
Interacts with Application 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
How many bytes does the TCP header add to a message?
24 bytes (if option used) or
20 bytes w/out option
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Packetization and Reassembly
Application
layer sees
message as a
single block
of data
TCP
packetization
FTP
FTP
TCP
TCP
IP
IP
receiver
sender
TCP reassembly
What size packet to use?
Done through
negotiations
Delivers incoming packets
as they arrive (e.g., Web pages) or
to wait until entire message arrives
(e.g., e-mail)
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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?
HTTP FTP SMTP
80
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TCP
Standards
What would be the other type of number used and why?
Non- Standard Port requiring further
configuration (provides greater security
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…
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
Transport Layer
Performs encapsulation on sending end
 Adds network layer header to
message segments
Network Layer
Data Link Layer
Performs decapsulation on receiving end
 Removes the network layer header at receiving end and passes
them up to the transport layer
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IP Packet Formats: IPv4 (24 bytes) vs. IPv6 (40 bytes)
IPv4
IPv6
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5.1 Types of Addresses
• Application Layer Address
• Assignment
• How do we get the URL’s IP address?
• How do this work?
• Address Resolution
Application Layer
Transport Layer
Network Layer
• Network Layer Address
• Assignment (Subnets)
• What is sent out to assign IP Address?
Data Link Layer
• Data Link Layer Address
• Assignment
• What is sent out if MAC Address is unknown?
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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
a given destination
 Kept by computers making routing decisions
Dest. Next
B
B
C
B
D
D
E
D
F
D
G
B
to reach
Routers
 Special purpose devices used to handle routing decisions on the
Internet
 Maintain their own routing tables
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Network Layers
Computer 1
Computer 2
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Data Link Layer (Chapter 4)
Responsible for moving messages from
one device to another
Network Layer
Controls the way messages are sent on media Data Link Layer
Physical Layer
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
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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
frame k-1
frame k
frame k+1
 Message delineation
 Frame length
 Frame field structure
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Network Layers
Computer 1
Computer 2
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Physical Layer (Chapter 3)
Includes network hardware and circuits
Network Layer
Data Link Layer
Physical Layer
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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3.1 Circuits
Physical connection (wire)
Configuration types (physical layout of the circuit):
 Point-to-Point Configuration
 Multipoint Configuration
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3.1.2 Data Flow (Transmission)
How does data flow through the circuit (circuits can be
designed to permit data flow)
Configuration types:
 Simplex
 Half-Duplex
 Full-Duplex
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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
Physical matter that carries the transmission
Types:
• Guided Media
• Radiated (Unguided) Media
http://whatis.techtarget.com/definition/0,,sid9_gci214198,00.html
http://www.iupui.edu/~ilight/index.html
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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: 100 bytes (could be variable)
• TCP: 24 bytes
• IP: 24 bytes
• Ethernet: 34 bytes
EFF = [# of data bytes]/ [#data bytes + # of overhead]
EFF = 500/(500+100+24+24+34) = 73%
What about an HTTP file of 4000 bytes?
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