Distributed Information Systems Lecture 4 - Networking, Lecture notes of Computers and Information technologies

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Networking &

Internetworking

Dr Simon Blake

Topics for this lecture

This lecture first introduces some fundamentalknowledge and concepts:

Types of networks

Underlying principles

•^

Packet transmission

-^

Data streaming

-^

Switching Schemes

-^

Protocols

-^

Routing

-^

Congestion

-^

Internetworking

• Internet Protocol (TCP/IP)– UDP and TCP– Firewalls

Networking fundamentals

– There are many networks composed of many

medias

(fibre, wireless, wire, etc.),

many

hardware devices

(routers, hubs, etc.)

, many

software

(protocols, stacks, drivers, etc.)

– These all affect the functionality of a DIS

Types of networks

• There are many different types of networks – We are focusing on:

•^

LANs (Local Area Networks)

-^

WANs (Wide Area Networks)

-^

MANs (Metropolitan Area Networks)

-^

Wireless

-^

Internetworks

100-

0.010-

Global

Internet

100-

0.010-

Global

Wireless WAN

5-

2-

0.15-1.5 kms

Wireless LAN

10

1-

2-50 kms

MAN

100-

0.010-

Global

WAN

1-

10-

1-2kms

LAN

Latency (ms)

Bandwidth (Mbps)

Range

Taken from Coulouris et al, 2003

WANs

Wide Area Networks

• Large range (satellites, optic fibres, microwaves)–

Lower bandwidth

,^

increased latency

• Networks that are distributed over greater distances– They employ routers to direct signals between networks– Routing causes delays (latency)– Travelling potentially large distances also takes time– Example of the fundamental limitations of communication over

large distances

•^

Assume the speed of light, assume UK to Australia ~ 10000 miles

-^

Europe to Australia will take at least 0.13 seconds

-^

Europe to Australia via global satellite will take at least 0.2 seconds

MANs & WANs

-^

Metropolitan networks

Networks installed in cities, typically copper or optic fibre

DIS can use these networks

Many different technologies, Ethernet, ATM, etc.

-^

Wireless networks

Local area (150 metres or less)

-^

Many types (IEEE 802.11, Bluetooth)

-^

Generally connect local devices, printers, computers, laptops to othernetworks

-^

Bluetooth is a personal LAN

Wide area (global)

-^

Cellular networks

-^

Slower than local area wireless networks

-^

In the process of being upgraded

Networking key concepts

• Topics we are going to consider

Packet transmission

Data streaming

Switching Schemes

Protocols

Routing

Congestion

Internetworking

Packets

Packet transmission

• Messages are passed from computer to computer over networks

via networks

• Messages come in various sizes– Its impractical to send long messages as this would block the

medium for others

• Thus messages are sliced into small sections, known as packets– A packet is a sequence of data with a defined size– Each packet contains information about its addresses (source

and destination)

Switching Schemes

-^

Transmitting information involves sending information betweennodes

-^

This involves switching between networks

-^

This requires a switching scheme

Switching schemes

• Broadcast– Circuit switching– Packet switching– Frame relay

Switching Schemes (cont..)

• Switching schemes
  • Broadcasting
    • No switching is required as everything transmitted

to everything

• i.e. Ethernet, Wireless, etc.
  • Circuit switching
    • Physical connections (circuits) are made• Involves physically connecting wires
      • Old telephone network technology

Protocols

• Networks rely on the use of protocols• A protocol is ‘

a

set of rules and formats

that are used in communication

’

• Protocol contains:
  • A specification of the sequence of messages• A specification of the format of the data

Protocols

Why use protocols??

• What happens if you expect a message in English and it arrives

in French? Can you read it?

• Computers too have to worry about the format of the messages

and sequence of messages!

• Protocols promote openness as they standardise development.

Some real world example

• Telephone conversation protocol

•^

Simple protocol ‘hello’ ‘goodbye’

• Telephone banking

•^

‘Hello’, ‘bank details’, ‘security check’, ‘transactions’

Protocols and layers

Network protocols are layered

• Layering promotes openness– Layering separates responsibilities

How does it work?

• Messages descend layers from sender– Before ascending layers at the receiver

message

sender

message Communicationmedium

receiver

Layer nLayer …Layer 2Layer 1

Layer nLayer ..Layer 2Layer 1

Protocol suites (OSI)

• Protocol suites
  • A protocol suite or protocol stack is complete

set of protocol layers

• The OSI model (Open Systems

Interconnection) is a commonly used exampleof a protocol suite

• The OSI model is a reference model