Lecture 4a: Communication and Networking
CSCI102 - Introduction to Information Technology B
ITCS905 - Fundamentals of Information Technology
Overview
Network standards and standardization bodiesThe ISO 7-layer reference model in general and its instantiation in TCP/IPCircuit switching and packet switchingStreams and datagrams
Overview
Physical layer networking concepts Theoretical basisTransmission mediaStandards
Data link layer concepts FramingError controlFlow control
Standards and Organisations- International:
ITU-T: International Telecommunications Union - Telecommunications Standardization Sector
Telephone and data communicationsFormerly the CCITT
ITU-R: Radiocommunications SectorRadio FrequenciesFormerly the CCIR
Standards and Organisations- International:
ISO - International Standards Organisation for all communication typesIETF – Internet Engineering Task Force
Standards and Organisations - American
ANSI: American National Standards Institute for data communicationsEIA: Electrical Industries Association for interfaces, connectors, facsimile, media IEEE: Institute of Electrical and Electronic Engineers specifically for 802 LAN standardsNIST: 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 bodiesIts a layered approach to network protocols involving encapsulation of packets at each level of the stack and the sub-layers
The OSI Stack
Transport
Data Link
Physical
Network
Session
Presentation
Application7
6
5
4
3
2
1
The OSI Stack
End-to-end connectionsSegments and reassembles data in proper sequenceSetup and teardown of “virtual circuits” (connection oriented)Can ensure segment delivery with error correction, recovery and flow control
Transport
Data Link
Physical
Network
Session
Presentation
Application7
6
5
4
3
2
1
The OSI Stack
Moves information to the correct address
Assembles and disassembles packetsAddresses and routes data packetsDetermines the best path for moving data through the network
Transport
Data Link
Physical
Network
Session
Presentation
Application7
6
5
4
3
2
1
The OSI Stack
It is up to the data link layer to detect and if necessary correct errorsThis is typically done by breaking the bit stream into distinct frames
Transport
Data Link
Physical
Network
Session
Presentation
Application7
6
5
4
3
2
1
Data Link Layer Concepts
Methods of framing includeCharacter countStart/end characters – character stuffingStart/end flags – bit stuffingPhysical layer coding violations
Data Link Layer Concepts
Error controlA noise burst on the line can destroy a frame completelyIdentified by
AcknowledgementsTimeouts
Individual packets can be retransmitted
Flow controlThrottles the sender to a rate that allows the receiver to keep up and handle all traffic
The OSI Stack
The OSI physical layer is concerned with the transmission of bits on the network
The order of bitsBit level error-checkingElectrical / mechanical characteristics
Transport
Data Link
Physical
Network
Session
Presentation
Application7
6
5
4
3
2
1
Network Transmission Media
To be propagated (sent) from one location to another, a signal must travel along a physical pathThe 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 mediaUnguided media
Network Transmission Media
There 4 basic types of guided media:Open wireTwisted pairCoaxial cableOptical Fibre
Unguided mediaRF propagation Microwave Satellite
OSI Instantiation in TCP/IP
Another widely used reference model is the TCP/IP model
OSI model
Application / User
Presentation
Session Control
Physical Link Control
Data Link Control
Network Control
Transport Controls
1
2
3
4
5
6
7
Layer TCP/ IP model
Application / User
Not Used
Not Used
Data Link Control
Internet Control
Transport Controls
Principles Used to Determine Layers
Level of conceptionAccurately defined dutyInternationally standardised protocolsMinimal information flow across layer boundaries Number of layers