Download Recap

Recap of Layers
Application, Data Link and Physical
Network Layers
Computer 1
Computer 2
2
Application Layer
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
3
Application Layer Characteristics
User
User
User
HTTP
SMTP
FTP
User
...
Other applications
TCP
IP
Local network
* From Business Data Communications (Manish Agrawal)
4
Application Architecture
Splitting the work across the client and the server
Basic Software Components:
•
•
•
•
Presentation Logic
Application Logic
Data Access Logic
Data
Types of Architectures:
• Host (or Server) Based
• Client Based
• Client/Server Based
5
How the web and email work:
Web:
• HTTP Request sent from a client to a server
• What is included in the request?
• Server responds back with an HTTP Response
• What is included in the response?
Email:
• SMTP Packet sent from client to server
• POP
• IMAP
6
Network Layers
Computer 1
Computer 2
7
Introduction - Transport layer
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
8
Network Layers
Computer 1
Computer 2
9
Introduction – Network Layer
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
10
Network Layers
Computer 1
Computer 2
11
Data Link Layer - Introduction
Responsible for moving messages from
one device to another
Network Layer
Controls the way messages are sent on media Data Link Layer
Organizes physical layer bit streams into
coherent messages for the network layer
Physical Layer
Major functions of a data link layer protocol
 Media Access Control
 Error Control
 Message Delineation
12
4.1 Media Access Control (MAC)
Controlling when and what computer transmit
 Important when more than one computer wants to send data at
the same time over the same, shared circuit
• Point-to-point half duplex links
• Multipoint configurations
Two possible approaches
 Controlled access
 Contention based access
13
Error Control - Sources of Errors and Prevention
Source of Error
Line Outages
What causes it
How to prevent it
Faulty equipment, Storms,
Accidents (circuit fails)
More important
mostly on analog
White Noise
Movement of electrons (thermal
energy)
Increase signal strength
(increase SNR)
Impulse Noise
Sudden increases in electricity
(e.g., lightning, power surges)
Shield or move the wires
Cross-talk
Multiplexer guard bands are too
small or wires too close together
Increase the guard bands, or
move or shield the wires
Echo
Poor connections (causing signal to
be reflected back to the source)
Fix the connections, or
tune equipment
Attenuation
Gradual decrease in signal over
distance (weakening of a signal)
Use repeaters or amplifiers
Intermodulation
Noise
Jitter
Signals from several circuits
combine
Move or shield the wires
Analog signals change (small
changes in amp., freq., and phase)
Tune equipment
Harmonic
Distortion
Amplifier changes phase (does not
correctly amplify its input signal)
Tune equipment
14
Major Functions of Error Control
• Error prevention
• Error detection
• Parity checks
• Check Sum
• Cyclic Redundancy Check (CRC)
• Error correction
• Retransmission
• Stop and Wait ARQ (A half duplex technique)
• Continuous ARQ (A full duplex technique)
• Forward Error Correction
15
Network Layers
Computer 1
Computer 2
16
Physical Layer - Overview
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.
17
Circuit Configurations & Data Flow
Configuration:
• Basic physical layout of the circuit
• Configuration types:
 Point-to-Point Configuration
 Multipoint Configuration
Data Flow (Transmission):
• Simplex
• Half-Duplex
• Full-Duplex
Multiplexing
18
Media
Physical matter that carries the transmission
• Signal transmitting properties of chosen media are important
Types:
• Guided Media
• Radiated (Unguided) Media
19
Data Transmission
Data - Representation of facts in a formalized manner suitable for
communication, interpretation, or processing by humans or by
automatic means
Signal - Detectable transmitted energy that can be used to carry
information
Bits in a message can be sent on:
 a single wire one after another (Serial transmission)
 multiple wires simultaneously (Parallel transmission)
Modes of transmission:
• Serial Mode
• Parallel Mode
20
Transmission Types
Digital Transmission (Digital Data) – Voltage Encoding
•
•
•
Unipolar
Bipolar NRZ
Bipolar RZ
Analog Transmission (Digital Data) – Modulation
•
•
•
Amplitude Modulation (AM)
Frequency Modulation (FM)
Phase Modulation (PM)
Digital Transmission (Analog Data)
 Requires a pair of special devices called Codec - Coder/decoder
• A device that converts an analog voice signal into digital form
• Converts it back to analog data at the receiving end
• Used by the phone system
21