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