inf4/msc computer networking
TRANSCRIPT
INF4/MSc
Computer Networking
Introduction & Overview
D K Arvind
dka AT inf.ed.ac.uk
2
We will look at:
– Network architecture principles
» From signals and wires to protocols
– Architecture of the Internet
– Wireless networks
» LANs, personal area, wireless sensor networks, wide/metropolitan area
3
Recommended Reading
• Much of the course is based on the textbook:
Computer Networking: A top-down approach featuring the Internet,
J. Kurose & K. Ross, Addison-Wesley
• Many other good books:
1.Communication Networks, Leon-Garcia & Widjaja. McGraw Hill.
2.Computer Networks, Andrew S. Tanenbaum. Prentice Hall.
3.Data and Computer Communications, William Stallings. Prentice
Hall.
• News on developments on comp.networking
4
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
• An insight into likely future developments in the field of networking
5
Assessment
• 75% of course mark
– Final exam
– Past papers available from the School archive
• 25% of course mark
– Two coursework assignments, equally weighted
• Coursework
1. Essay on convergence in telecommunication networks
[Issued on 19th September 2011; Deadline: 20th October 2011]
2. Issued on 20th October 2011; Deadline: 24th November 2011
• Plagiarism: don’t do it!
– Read the relevant informatics and university web pages
6
Course admin
• Lecturers:
– Prof. DK Arvind
– Dr. Mahesh Marina
• Two lectures / week
– 10 – 10:50am on Mondays, 7 Bristo Square, Lecture Theatre 1
– 10 – 10:50am on Thurdays, 7 Bristo Square, Lecture Theatre 1
(except Thursday, 22nd September, 2011)
• 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 security of the critical infrastructure
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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
TransportationTransportation
Oil & Natural Gas
EE
LL
EE
CC
TT
RR
II
CC
II
TT
YY
Potable & Waste WaterPotable & Waste Water
Emergency ResponseEmergency Response
Government
TT
EE
LL
EE
CC
OO
MM
Banking & FinanceBanking & Finance
Water for cooling, emissions control
Water for production, cooling, emissions control
Fire suppression
Cooling
Co
mm
un
ica
tion
s
SCADA
SCADA
Trading, transfers
SCADA
Co
mm
un
ica
tion
s
Location, EM contact
Currency (US Treasury; Currency (US Treasury; Federal Reserve )Federal Reserve )
DOE;DOE;DOTDOT
Regulations & enforcement Regulations & enforcement FERC; DOEFERC; DOE
Personnel/Equipment Personnel/Equipment (Military)(Military)
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Fin
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FASB; IRCFASB; IRC
FEMA; DOTFEMA; DOT
DOTDOT
EPAEPA
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 systemsSwitches, 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, ITe-commerce, IT
Pumps, lifts, control systemsPumps, lifts, control systems
Signalization, switches,control systems
Signalization, switches,control systems
e-government,ITe-government,IT
Medical equipmentMedical equipment
TransportationTransportation
Oil & Natural Gas
EE
LL
EE
CC
TT
RR
II
CC
II
TT
YY
Potable & Waste WaterPotable & Waste Water
Emergency ResponseEmergency Response
Government
TT
EE
LL
EE
CC
OO
MM
Banking & FinanceBanking & Finance
Water for cooling, emissions control
Water for production, cooling, emissions control
Fire suppression
Cooling
Co
mm
un
ica
tion
s
SCADA
SCADA
Trading, transfers
SCADA
Co
mm
un
ica
tion
s
Location, EM contact
Currency (US Treasury; Currency (US Treasury; Federal Reserve )Federal Reserve )
DOE;DOE;DOTDOT
Regulations & enforcement Regulations & enforcement FERC; DOEFERC; DOE
Personnel/Equipment Personnel/Equipment (Military)(Military)
Fin
an
cin
g, re
gu
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, & e
nfo
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Fin
an
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FASB; IRCFASB; IRC
FEMA; DOTFEMA; DOT
DOTDOT
EPAEPA
Detection, 1st responders, repair
TransportationTransportation
Oil & Natural Gas
EE
LL
EE
CC
TT
RR
II
CC
II
TT
YY
Potable & Waste WaterPotable & Waste Water
Emergency ResponseEmergency Response
Government
TT
EE
LL
EE
CC
OO
MM
Banking & FinanceBanking & Finance
TransportationTransportationTransportationTransportation
Oil & Natural GasOil & Natural Gas
EE
LL
EE
CC
TT
RR
II
CC
II
TT
YY
EE
LL
EE
CC
TT
RR
II
CC
II
TT
YY
Potable & Waste WaterPotable & Waste WaterPotable & Waste WaterPotable & Waste Water
Emergency ResponseEmergency ResponseEmergency ResponseEmergency Response
GovernmentGovernment
TT
EE
LL
EE
CC
OO
MM
TT
EE
LL
EE
CC
OO
MM
Banking & FinanceBanking & FinanceBanking & FinanceBanking & Finance
Water for cooling, emissions control
Water for production, cooling, emissions control
Fire suppression
Cooling
Water for cooling, emissions controlWater for cooling, emissions control
Water for production, cooling, emissions controlWater for production, cooling, emissions control
Fire suppressionFire suppression
CoolingCooling
Co
mm
un
ica
tion
s
SCADA
SCADA
Trading, transfers
SCADA
Co
mm
un
ica
tion
s
Location, EM contact
Co
mm
un
ica
tion
s
SCADA
SCADA
Trading, transfers
SCADA
Co
mm
un
ica
tion
s
Location, EM contact
Co
mm
un
ica
tion
s
SCADA
SCADA
Trading, transfers
SCADA
Co
mm
un
ica
tion
s
Location, EM contact
SCADA
SCADA
Trading, transfers
SCADA
Co
mm
un
ica
tion
s
Location, EM contact
Currency (US Treasury; Currency (US Treasury; Federal Reserve )Federal Reserve )
DOE;DOE;DOTDOT
Regulations & enforcement Regulations & enforcement FERC; DOEFERC; DOE
Personnel/Equipment Personnel/Equipment (Military)(Military)
Fin
an
cin
g, re
gu
latio
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, & e
nfo
rce
me
nt
Fin
an
cin
g, re
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latio
ns
, & e
nfo
rce
me
nt
FASB; IRCFASB; IRC
FEMA; DOTFEMA; DOT
DOTDOT
EPAEPA
Currency (US Treasury; Currency (US Treasury; Federal Reserve )Federal Reserve )
DOE;DOE;DOTDOT
Regulations & enforcement Regulations & enforcement FERC; DOEFERC; DOE
Personnel/Equipment Personnel/Equipment (Military)(Military)
Fin
an
cin
g, re
gu
latio
ns
, & e
nfo
rce
me
nt
Fin
an
cin
g, re
gu
latio
ns
, & e
nfo
rce
me
nt
FASB; IRCFASB; IRC
FEMA; DOTFEMA; DOT
DOTDOT
EPAEPA
DOE;DOE;DOTDOT
Regulations & enforcement Regulations & enforcement FERC; DOEFERC; DOE
Personnel/Equipment Personnel/Equipment (Military)(Military)
Fin
an
cin
g, re
gu
latio
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Fin
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FASB; IRCFASB; IRC
FEMA; DOTFEMA; DOT
DOTDOT
EPAEPA
Detection, 1st responders, repair
Detection, 1st responders, repair
Detection, 1st responders, repair
Source: Miriam Heller
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The Plant: A Complex Environment
sec
msec
1 sec
secs
min
hours
Plant
Servers
Other
Computing
Devices
Business Management
Area Servers Plant
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
Smartine
Transmitters
PLC
Gateway
Other
Subsystems
PLC
Logic Manager Process
Manager
Advanced
Process
Manager
Transmitters
Control Network
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
– What’s the use of email if only a few people use it?
11
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
– Requires low latency, high-throughput (for quality sound), low jitter
12
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,…
13
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 t1
Network
• Cost-effective design necessary to meet user requirements
– Networks usually designed to carry specific types of information
– Voice, TV, bits, characters etc.
14
• 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
The N2 Problem
15
• 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
Metropolitan
a
c
b
d g
National
• 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
17
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
18
• 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
Switching
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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?
Factors in Communication Network Evolution
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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
– Humans: experts, general public
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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
Multiple technologies overlap
22
– 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.
Regulation
23
– 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
Market
24
– 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)
Standards