Transcript Lecture 4a: Communication and Networking

Lecture 4a: Communication
and Networking
CSCI102 - Introduction to Information Technology B
ITCS905 - Fundamentals of Information Technology
Overview
Network standards and
standardization bodies
The ISO 7-layer reference model in
general and its instantiation in
TCP/IP
Circuit switching and packet switching
Streams and datagrams
Overview
Physical layer networking concepts
Theoretical basis
Transmission media
Standards
Data link layer concepts
Framing
Error control
Flow control
Standards and OrganisationsInternational:
ITU-T: International Telecommunications
Union - Telecommunications
Standardization Sector
Telephone and data communications
Formerly the CCITT
ITU-R: Radiocommunications Sector
Radio Frequencies
Formerly the CCIR
Standards and OrganisationsInternational:
ISO - International Standards
Organisation for all communication
types
IETF – Internet Engineering Task
Force
Standards and Organisations American
ANSI: American National Standards
Institute for data communications
EIA: Electrical Industries Association for
interfaces, connectors, facsimile, media
IEEE: Institute of Electrical and
Electronic Engineers specifically for 802
LAN standards
NIST: National Institute of Standards and
Technology the all American equivalent to
the ISO (of course!!)
The OSI Stack
Proposed by the International
Standards Organisation (ISO) and
other standards bodies
Its a layered approach to network
protocols involving encapsulation of
packets at each level of the stack and
the sub-layers
The OSI Stack
7
Application
6
Presentation
5
Session
4
Transport
3
Network
2
Data Link
1
Physical
The OSI Stack
7
Application
6
Presentation
5
Session
4
Transport
3
Network
2
Data Link
1
Physical
End-to-end connections
Segments and reassembles
data in proper sequence
Setup and teardown of
“virtual circuits”
(connection oriented)
Can ensure segment
delivery with error
correction, recovery and
flow control
The OSI Stack
7
Application
6
Presentation
5
Session
4
Transport
3
Network
2
Data Link
1
Physical
Moves information to the
correct address
Assembles and disassembles
packets
Addresses and routes data
packets
Determines the best path
for moving data through the
network
The OSI Stack
7
Application
6
Presentation
5
Session
4
Transport
3
Network
2
Data Link
1
Physical
It is up to the data link
layer to detect and if
necessary correct errors
This is typically done by
breaking the bit stream
into distinct frames
Data Link Layer Concepts
Methods of framing include
Character count
Start/end characters – character
stuffing
Start/end flags – bit stuffing
Physical layer coding violations
Data Link Layer Concepts
Error control
A noise burst on the line can destroy a frame
completely
Identified by
Acknowledgements
Timeouts
Individual packets can be retransmitted
Flow control
Throttles the sender to a rate that allows the
receiver to keep up and handle all traffic
The OSI Stack
7
Application
6
Presentation
5
Session
4
Transport
3
Network
2
Data Link
1
Physical
The OSI physical layer is
concerned with the
transmission of bits on the
network
The order of bits
Bit level error-checking
Electrical / mechanical
characteristics
Network Transmission Media
To be propagated (sent) from one
location to another, a signal must
travel along a physical path
The physical path that is used to
carry a signal between a signal
transmitter and a signal receiver is
called the "transmission medium"
Network Transmission Media
There are two types of transmission
media
Guided media
Unguided media
Network Transmission Media
There 4 basic types of guided media:
Open wire
Twisted pair
Coaxial cable
Optical Fibre
Unguided media
RF propagation
Microwave
Satellite
OSI Instantiation in TCP/IP
Another widely used
reference model is the
TCP/IP model
Layer
OSI model
1
Application /User
Application /User
2
Presentation
Not Used
3
Session Control
Not Used
4
Transport Controls
Transport Controls
5
Network Control
Internet Control
6
Data Link Control
Data Link Control
7
Physical Link Control
TCP/IP model
Principles Used to Determine
Layers
Level of conception
Accurately defined duty
Internationally standardised
protocols
Minimal information flow across layer
boundaries
Number of layers