Lecture 1: Introduction & Overview

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INF4/MSc

Computer Networking

Lecture 1: Introduction & Overview

D K Arvind

dka AT inf.ed.ac.uk

IF 2.18

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We will look at:

– Network architecture principles

» From signals and wires to protocols

– Architecture of the Internet

– Wireless networks

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Reading

• Much of the course is based on the textbook:

Computer Networking: A top-down approach featuring the Internet,

(3/e) J. Kurose & K. Ross, Addison-Wesley, 2005

• Many other good books:

1.Communication Networks (2e), Leon-Garcia & Widjaja. McGraw Hill,

2004

– Last year’s book. Still OK, if you got it second hand, or from the library

2.Computer Networks (4e), Andrew S. Tanenbaum. Prentice Hall,

2003

3.Data and Computer Communications (7e), William Stallings.

Prentice Hall, 2003

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Learning Outcomes

• Knowledge of key concepts, protocols and algorithms in networking

• An understanding of the complexity of networks, their structure and

utility

• The ability to apply knowledge to networking applications, to network

infrastructure and to network management

• The ability to write and present clear and concise description of

complex issues

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Assessment

• 75% of course mark

– Final exam

– Past papers available from the School archive

• 25% of course mark

– Two coursework assignments, equally weighted

• Coursework (look web page for dates, etc)

1.Essay on convergence in telecommunication networks 2.Technical report based on a survey of papers

• Plagiarism: don’t do it!

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Course admin

• Lecturers: DK Arvind & Mahesh Marina

• Two lectures / week

– 10am Mon, WRB G.04 – 10am Thu, WRB G.04

• Course web page:

www.inf.ed.ac.uk/teaching/courses/cn

• Newsgroup:

eduni.inf.ug4

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Networked Critical Infrastructure

• A modern state has a network of

control systems for the measurement and change of the infrastructure state for safe,

uninterrupted, and efficient delivery of utilities (electricity, water), of services (telecommunication, health,

transportation, banking), and of essential commodity (gas, oil)

• A network of distributed sensors for collecting data and software for extracting and interpreting information to raise the

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Interdependencies, Interdependencies,…

Switches, control systems Storage, pumps, control systems, compressors e-commerce, IT Pumps, lifts, control systems Signalization, switches, control systems e-government, IT Medical equipment

Transportation

Oil & Natural Gas

E

L

E

C

T

R

I

C

I

T

Y

Potable & Waste Water

Emergency Response

Government

T

E

L

E

C

O

M

Banking & Finance

Water for cooling, emissions control

Water for production, cooling, emissions control Fire suppression Cooling C o m m u n ic a tio n s SCADA SCADA Trading, transfers SCADA C o m m u n ic a tio n s Location, EM contact Currency (US Treasury;

Currency (US Treasury;

Federal Reserve ) Federal Reserve ) DOE; DOE; DOT DOT

Regulations & enforcement

FERC; DOE FERC; DOE Personnel/Equipment Personnel/Equipment (Military) (Military) F in a n c in g, regu lati o n s, & en fo rc em ent Fi na nci n g, r e gul a tio n s , & enforcem ent FASB; IRC FASB; IRC FEMA; DOT FEMA; DOT DOT DOT EPA EPA Detection, 1st_responders, repair

Switches, control systems Storage, pumps, control systems, compressors e-commerce, IT Pumps, lifts, control systems Signalization, switches, control systems e-government, IT Medical equipment

Switches, control systems Switches, control systems Storage, pumps, control systems, compressors e-commerce, IT Pumps, lifts, control systems Signalization, switches, control systems e-government, IT Medical equipment Storage, pumps, control systems, compressors Storage, pumps, control systems, compressors e-commerce, IT e-commerce, IT Pumps, lifts, control systems Pumps, lifts, control systems Signalization, switches, control systems Signalization, switches, control systems e-government, IT e-government, IT Medical equipment Medical equipment

Transportation

Oil & Natural Gas

E

L

E

C

T

R

I

C

I

T

Y

Potable & Waste Water

Emergency Response

Government

T

E

L

E

C

O

M

Banking & Finance

Water for production, cooling, emissions control Fire suppression Cooling Co m mun ic ati o n s SCADA SCADA Trading, transfers SCADA Com mun ication s Location, EM contact Currency (US Treasury;

FERC; DOE FERC; DOE Personnel/Equipment Personnel/Equipment (Military) (Military) F in a n c in g, regu lati o n s, & en fo rc em ent Fi na nci n g, r e gul a tio n s , & enforcem ent FASB; IRC FASB; IRC FEMA; DOT FEMA; DOT DOT DOT EPA EPA Detection, 1st_responders, repair

Transportation

Oil & Natural Gas

E

L

E

C

T

R

I

C

I

T

Y

Potable & Waste Water

Emergency Response

Government

T

E

L

E

C

O

M

Banking & Finance

Transportation

Oil & Natural Gas

E

L

E

C

T

R

I

C

I

T

Y

E

L

E

C

T

R

I

C

I

T

Y

Potable & Waste Water

Emergency Response

Government

T

E

L

E

C

O

M

T

E

L

E

C

O

M

Banking & Finance

Water for production, cooling, emissions control

Fire

suppression

Cooling Water for cooling,

emissions control Water for cooling, emissions control

Water for production, cooling, emissions control

Water for production, cooling, emissions control Fire suppression Fire suppression Cooling Cooling Co m mun ic ati o n s SCADA SCADA Trading, transfers SCADA Com mun ication s Location, EM contact Co m mun ic ati o n s SCADA SCADA Trading, transfers SCADA Com mun ication s Location, EM contact Co m mun ic ati o n s SCADA SCADA Trading, transfers SCADA Com mun ication s Location, EM contact SCADA SCADA Trading, transfers SCADA Com mun ication s Location, EM contact Currency (US Treasury;

FERC; DOE FERC; DOE Personnel/Equipment Personnel/Equipment (Military) (Military) F in a n c in g, regu lati o n s, & en fo rc em ent Fi na nci n g, r e gul a tio n s , & enforcem ent FASB; IRC FASB; IRC FEMA; DOT FEMA; DOT DOT DOT EPA EPA

FERC; DOE FERC; DOE Personnel/Equipment Personnel/Equipment (Military) (Military) F in a n c in g, regu lati o n s, & en fo rc em ent Fi na nci n g, r e gul a tio n s , & enforcem ent FASB; IRC FASB; IRC FEMA; DOT FEMA; DOT DOT DOT EPA EPA DOE; DOE; DOT DOT

FERC; DOE FERC; DOE Personnel/Equipment Personnel/Equipment (Military) (Military) F in a n c in g, regu lati o n s, & en fo rc em ent Fi na nci n g, r e gul a tio n s , & enforcem ent FASB; IRC FASB; IRC FEMA; DOT FEMA; DOT DOT DOT EPA EPA Detection, 1st_responders, repair Detection, 1st_responders, repair Detection, 1st_responders, repair

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The Plant: A Complex Environment

μ sec

msec

1 sec

secs

min

hours

Plant Servers Other Computing Devices Business Management Area ServersPlant Network Modules Network Gateway Network Gateway Process Management Subnetwork Gateway Application Module History Module Personal Computer Network Manager Control Stations Archive Replay Module Additional CN Modules Fiber Optics Network Interface Module Other Data Hiway Boxes Multifunction Controller Extended Controller Basic Controller Advanced Multifunction Controller LocalProcessors Su bn etw ork C O N T R O L N E T W O R K Smartine Transmitters PLC Gateway Other Subsystems PLC Logic ManagerProcess Manager Advanced Process Manager Transmitters Control Networ Extenders Field Management

Source: TRUST

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Service-oriented view of computer networks

• A computer network provides a communication service, i.e. enables the

exchange of information between computers (and their users) that are

located at various geographical locations

• Communication service is ubiquitous and an essential infrastructure of

modern society

• Comparable in value with transportation, water, electricity,…

• Because there are no limits to information, networking enables further

services

– For example the telephone network enables fax, voicemail, electronic banking, ,…

– Computer networks enable email, information search, electronic commerce, …

• Value of the network depends on its size: the larger, the better

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Characteristics of the communicated information

• Non-interactive

:

– Text, pictures, music, video

– Two sub-categories: streaming or not

» jitter is most important for streaming multimedia

• Interactive

:

– Teleconferencing, videoconferencing, instant msg/chating

Size is an important factor

– Compression (lossy/lossless) can help, opens up a computation vs

communication trade-off

Worst case: Musicians playing instruments together through the

network

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Characteristics of the communication services

• Connection-oriented

(think telephone)

– Receiver is active while information is transmitted

– Must establish connection, before any data is transmitted

• Connectionless

(think [e]mail)

– Data transmission can start earlier

• Other service characteristics:

– Confirmed – unconfirmed delivery

– Quality of service characteristics:

» Performance (delay, throughput, delay-variation…) » Error rate, security,…

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Approaches to Network Design

• Networks provide connectivity between users at the network edge

through a transmission system, the network core

– Using various types of physical media (wires, radio, optical fibre, etc.)

and devices (switches, routers, multiplexers, etc.)

– Network core equipment is fundamentally different to equipment at

the network edge

t₀ _t

1

Network

• Cost-effective design necessary to meet user requirements

– Networks usually designed to carry specific types of information

– Voice, TV, bits, characters etc.

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• Pairwise interconnections would require N*(N-1) links

– or a central switching access network, and just N access links

• Networks consist of point-to-point links interconnected by switches

– for a multi-hop path, routing decides which path to take at a switch – forwarding actually moves the data in the direction decided

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• Connections between local communities use trunks between local

switches

– Multiplexers concentrate the traffic over the more expensive line

– Demultiplexers separate out the individual parts of the traffic for distribution

A A a c b d γ α β

• Networks are hierarchical:

– Metropolitan networks interconnect access networks – Regional networks connect metropolitan networks

– National networks, international networks etc. using backbone networks

Larger Networks

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– Networks of networks

– The Internet Protocol (IP) was developed to provide connectionless transfer of packets across an internet

– The component networks are interconnected by packets switches called

gateways or routers, which direct the transfer of packets

– IP provides a best-effort service i.e. it does its best to deliver a packet, but it does not guarantee successful delivery

G G G G G net 1 net 2 net 3 net 4 net 5 G G = gateway

Internetworks

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Addressing required to identify source and destination

end-points

– Hierarchical addressing uses common prefixes for end-points in the

same geographical areas

» Facilitates routing

» As in a postal address: country, county, town, district, street, number; the Post Office batches mail for countries and for towns, districts,

streets etc.

– Hierarchical addressing in Wide Area Networks e.g. the Internet

» Also facilitates routing

– Flat addressing in Local Area Networks e.g. ethernets

» Adequate for the typically small number of local area end-points

Addressing

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• Circuit-switching

– In early communication networks, switching was performed at the electrical signal level, creating a real circuit end to end

– In modern digital transmission media, circuit-switching means allocation of dedicated resources (e.g. a share of a link’s transmission capacity) end to end – Switches forward information one bit at a time (in theory)

• Packet/message switching

– Switches store whole packet and then forward it using the full link transmission capacity

– Connectionless or datagram

» Each packet/message routed independently of all other packets

– Virtual circuit

» A route set up through switches and links in the network » All subsequent packets forwarded along the same path

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Technology, Regulation, Markets, Standards

– Availability of a technology does not mean it will sell

– Never very clear beforehand whether a market exists for a product or service – The move away from monopoly telecomms suppliers makes standards

essential Technology Regulation Market Standards Can it be built? Will it sell? Is it allowed? Will it inter-operate?

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Computer network uses

• Resource sharing

– Printers, disks, specialised hardware, …

• Information sharing

– Database access

• Human communication

– Email, Voice-over-IP, file-sharing (pictures, music,…)

• Commerce

– Shopping on-line, banking, …

• Entertainment

– Movies, games

• Remote access/monitoring/working

“Users” of the network

– Computers

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• Limited by fundamental physical laws

– In most cases substantial opportunities for improvement remain

• Key technologies

– Transmission systems

– Computer processing capacity (Moore’s Law)

Time Cumulative Experience Technical Expert Entrepreneur Professional Manager

Technology

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– Telecomms services have always been government regulated

» until very recently as state monopolies

– Deregulation and privatisation of monopolies

» more competition in long distance telecomms

» cable television and satellite broadcasting competition to terrestrial

– Radio spectrum allocation

» has always been closely controlled nationally and internationally » cellular telephone frequencies, 900MHz and 1800 MHz allocations » 3G spectrum auctions

– Office of Communications (Ofcom) in the UK

» promoting consumer interest » maintaining effective competition

» ensuring services to meet all reasonable demands e.g. emergency services, directory information, rural services etc.

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– Usefulness of a service often depends on there being a critical mass of subscribers e.g. email, SMS

– Economies of scale often vital to sustain services and develop new ones

» cable and satellite TV » mobile phones

– Entrepreneurs always searching for the next “Killer App”

» SMS messaging on mobile phones a success » WAP a failure

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– Agreements, industry-wide, with national and international scope – Ensure interoperability of equipment made by different vendors

» competition reduces prices

– Physical standards such as plugs and sockets e.g. USB – Usage standards such as communications protocols

» whether implemented by software or hardware

– Can arise initially as de facto standards from a successful product

» e.g. ethernet

» internationally standardised later

– or developed by subcommittees of standards bodies

» Internet Engineering Task Force (IETF)

» Institute for Electrical and Electronics Engineers (IEEE) » International Telecommunications Union (ITU)

» International Standards Organisation (ISO)

Lecture 1: Introduction & Overview

INF4/MSc

Computer Networking