CCM 4300 Lecture 2 - JSinti · 2012-10-21 · CCM 4300 Lecture 2 Computer Networks: ... through the...
Transcript of CCM 4300 Lecture 2 - JSinti · 2012-10-21 · CCM 4300 Lecture 2 Computer Networks: ... through the...
CCM 4300 Lecture 2Computer Networks: Wireless and Mobile Communication
Systems
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Systems
Dr Shahedur Rahman
School of Science and Technology
Recap of Last Session
�defined a computer network and identified some of the basic components.
� explored the history of computers and computer networks and how they have evolved.
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networks and how they have evolved.
� identified some of the advantages and disadvantages of using computer networks.
Session Content
� Classification of computer networks
� Switched
� circuit switching
� packet switching
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� packet switching
� broadcast networks
� scale
� Network standards
Lesson objectives
� To introduce a taxonomy of computer network :
�identify basic transmission technologies
�Classify different networks based on their scale.
�Understand the importance of standards
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�Understand the importance of standards
� There is no generally accepted taxonomy into which all
computer networks fit, but two dimensions stand out as
important:
� Transmission technology
� Switched network
Classification of computer networks
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� Switched network
� Broadcast network
� Scale
�LANs, MANs, WANs, HANs, PANs, CANs, WLANs
� Switched networks
– data are transferred from source to destinationthough a series of intermediate nodes. The nodesprovide the switching facility that will move data totheir destination
circuit-switched network – a dedicated, physical
Transmission Technology
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circuit-switched network – a dedicated, physicalcircuit is first established between the source anddestination nodes before the data transmissiontakes place
packet-switched network – messages are firstpartitioned into smaller units called packets, whichare that sent to the destination node one at a time viaintermediate switches
Circuit Switching
End-end resources reserved for “call”
� call setup required
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� call setup required
� dedicated resources: no sharing
� Release of resources
Circuit Switching
network resources (e.g., bandwidth) divided into “pieces” and pieces allocated to calls
� For instance we can divide link bandwidth using
� frequency division
time division
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� time division
� One of the main advantages of circuit switching is that some QoS can be guaranteed
� Example of Circuit switching is the PSTN (thetelephone network). Here each user has 64Kbsguaranteed during the call
� What are the disadvantages of Circuit switching?
Why packet switching?
� Computer data transmission is normally bursty innature
� Bursty traffic refers to an uneven pattern of datatransmission: sometime very high data transmissionrate while other time it might be very low.
In this case circuit network is wasteful of network
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� In this case circuit network is wasteful of networkbandwidth since must have sufficient channelbandwidth to handle burst level of traffic which isthen used most of the time
� The solution is packet switching which allowssharing
Packet Switching
A
B
C10 MbsEthernet
1.5 Mbs
45 MbsPackets are bufferedwaiting for a free output
link
When the link is free the packet is sent
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� Packet-switching is like sending a standard letter through the post
� other analogies?
D E
� This schema of data transfer is often called store-and-forward
Packet Switchingeach end-end data stream divided into packets
� user A, B packets sharenetwork resources
� each packet uses full link
resource contention:
� aggregate resource demand can exceed amount available
� congestion: packets
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Bandwidth division into “pieces”
Dedicated allocation
Resource reservation
� each packet uses full link bandwidth
� resources used as needed
� congestion: packets queue, wait for link use
Packet Switching
• What if messages were sent as single units?
• Very long packets can increase the delay
incurred at each switch until the link is free
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• Short packets can reduce the delay and fixed
packets can allow hardware optimisation
Packet switching versus circuit switching
� E.g., 1 Mbit link
� each user:
� 100Kbps when “active”
� active 10% of time
Packet switching allows more users to use network!
1−35
i
p
i1 − p( )
35− i
i=0
10
∑
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� active 10% of time
� circuit-switching:
� 10 users
� packet switching:
� with 35 users, probability > 10 active less than .0004� (probability that out of 35, ten or less more transmitting at the same time is
0.0004)
N users
1 Mbps link
Packet switching vs circuit switching
A circuit-switched network can guarantee a certain amountof end-to-end bandwidth for the duration of a call.
Most packet-switched networks today (including theInternet) cannot make any end-to-end guarantees forbandwidth.
Why should I choose circuit switching?
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bandwidth.
Extra mechanisms are required for flow control, congestioncontrol, and QoS.
A circuit-switched network is suitable for application withlong sessions with predictable smooth band-width requirements.
Packet switching vs circuit switching
When connections are short-lived the setup delaymay represent a large part of the total connectiontime, thus reducing the network's capacity.
Why should I choose packet switching?
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time, thus reducing the network's capacity.
Reserved resources cannot be used by any otherusers even if the circuit is inactive, which mayfurther reduce link utilisation.
� Broadcast networks
– there are no intermediate switching nodes. The
network share a single communication medium or
channel
packet radio and satellite networks – stations
Transmission Technology
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packet radio and satellite networks – stations
transmit and receive via antenna and share the same
channel or radio frequency
Local Area Networks (LANs) – transmission by any
one station propagates the length of the medium
� Local Area Networks (LANs)
� LANs interconnects computing
resources within a moderately (IEEE
usually relates this to 10 km or about
6 miles or less in radius) sized
geographical area
Scale
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� This can include a room, several
rooms within a building, or several
buildings of a campus (e.g. Hendon
campus)
� Various topologies are possible for
LANs such as bus, star, ring, mesh
� MANs interconnects computing resources that span a
metropolitan area
� The main reason for ever distinguishing MANs as special
category is that a standard had been adopted for them
(called Distributed Queue Dual Bus (DQDB, IEEE 802.6)
Metropolitan Area Network (MAN)
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� MANs generally refer to networks that span a larger
geographical area than LANs but a smaller geographical
area than WANs
. A MAN might be owned and operated by a single
organization, but it usually will be used by many individuals and organizations.
� MANs might also be owned and operated as public
utilities. They will often provide means for internetworkingof local networks.
Metropolitan Area Network (MAN)
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of local networks.
� For instances this include
�Companies with buildings
located throughout a local
county or city
�A large campus
Internet StructureSprint London backbone network
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� WANs Interconnects computing resources that arewidely separated geographically (usually over 100 Km). This includes towns, cities, states and countries (e.g.The Internet)
� A WAN can be thought as consisting of a collection ofLANs
Wide Area Networks (WANs)
�Most WANs consists of twodistinct components:
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distinct components:
�transmission lines, whichmoves data between
nodes
�switching elements(router), which usesspecialised computers toconnect two or moretransmission lines.
WAN vs LAN
1. Two computers communicating through a WAN
2. Two computers communicating through a LAN
• Which computers are exchanging data faster?
• LAN usually operates at much higher ratescompared to WAN. This is mainly due to the
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compared to WAN. This is mainly due to theproximity of the computers and the lack ofcongestion. It is common to experience up to 90mbps in a LAN while achieving 10 to 20mbps isalready a great achievement for WAN.
WAN vs LAN
• Is a LAN more secure than a WAN?
• Conceptually LAN could be more securedue to the fact that all the computers are
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due to the fact that all the computers arewithin a specific area and are physicallyeasier to secure. The data on a wide areanetwork could pass insecure networks inorder to reach its intended destination.
PAN – Personal Area Network�A personal area network (PAN) is a computer network used forcommunication among computer devices, including telephones andpersonal digital assistants, in proximity to an individual's body.
�The devices may or may not belong to the person in question. PANscan be used for communication among the personal devices themselves(intrapersonal communication), or for connecting to a higher levelnetwork and the Internet (an uplink).
�A PAN covers the few meters that surround the user’s workspace
� It provides the ability to synchronise computers, access localperipherals such a printers and pocket devices
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peripherals such a printers and pocket devices
�It can be made possible using IrDA, Bluetooth, ZigBee, USB
� A home area network (HAN) is a residential local area network
�It is used for communication between digital devices typically deployed
in the home, usually a small number of personal computers and
accessories, such as printers and mobile computing devices.
� An important function is the sharing of Internet access, often a
broadband service through a cable tv or Digital Subscriber Line (DSL)
provider.
�Additionally, a home server may be added for increased functionality.
�Intended to provide the home with an infrastructure to interconnect a
variety of homes appliances
HAN – Home Area Network
variety of homes appliances
� Enable them to be accessed through the Internet through a central
home gateway.
� Therefore, a home computer network, will in the future allow multiple
computers as well as multiple devices to connect with a network
protocol.
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� provides access up to a range of few hundredmeters, e.g. an office block. 802.11b
�A single access point, wired at a fixed location,supports a number of wireless users within aspecified range without the need of cumbersome
CAN – Company Area Network
specified range without the need of cumbersomeEthernet cabling to form a star topology.
�CANs have also emerged as hotspots in variouslocations such as coffee shops and airportsproviding users with Internet access
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� Is a vehicle bus standard designed to allowmicrocontrollers and devices to communicate witheach other within a vehicle without a hostcomputer
� CAN uses message based protocols, designedspecifically for automotive applications but nowalso used in other areas such as industrialautomation and medical equipment.
CAN – Controller Area Network
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� A modern automobile mayhave as many as 70electronic control unit(engine control unit, airbags,cruise control). A CAN can beused to connect them together.
Network standards� “Many network vendors exist each with its own ideas
about how things should be done. Withoutcoordination there would be a complete chaos. Theonly way out is to agree on some networkstandards.”
Andrew S. Tanenbaum – Computer network 2003
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� A standard is a stated norm or requirements abouttechnical systems. It is usually a document thatestablishes uniform criteria, methods, processes andpractises.
� Not only standards allow different computers tocommunicate, but they also increase the market forthe products that comply with the standard
Network standards� Network standards fall into two categories:
� De facto (Latin for “from the fact”): they havenot been approved by any organised body butthey have been adopted as a standard because oftheir widespread use. For instance Unix, MP3,PDF, DOC, IBM PC format
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PDF, DOC, IBM PC format
� De jure standards (Latin for ‘by Law’): they areformal, legal standards adopted by someauthorised standardisation body.
Network Standards - cont� Recognised body can be classified into four major categories: (1) National, (2) Regional, (3) International, (4) Industry, Trade, and Professional.
� National Standards Organisations – generally responsible for standards within a nation
- British Standards Institute (BSI)
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- British Standards Institute (BSI)
- American National Standards Institute (ANSI)
Network Standards - cont�Regional Standards Organisation – restrict their activity to a specific geographical region but generally influences standards outside their regions
- European Telecommunications Standards Institute (ETSI) Previously CEPT
- European Committee for Standardization (CEN)
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- European Committee for Standardization (CEN)
- European Computer Manufactures’ Association (ECMA)
� International Standards Organization – promotes standards for worldwide use
- International Standards Organisation (ISO)
- International Telecommunications Union (ITU) formally known as the CCITT - Comité Consultatif Internationale Télégraphique et Téléphonique.
Network Standards
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Télégraphique et Téléphonique.
• ITU major divisions:
•Consists of ITU -T, which is responsible for
communications, interfaces, and other standards
relating to telecommunications
•I series - Integrated Services Digital Network
Network Standards
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•I series - Integrated Services Digital Network
(ISDN)
• X series - Data communication networks (e.g.
X.25)
• ITU – R, which is responsible for allocation of
frequency band in the electromagnetic spectrum for
telecommunications, and for making recommendation
relating to radio communications.
� Industry, Trade and Professional Standards Organizations –restrict their activity to member interest areas but generally influence other areas
- Electronic Industry Association (EIA)
- The Institute of Electrical and Electronics Engineers
- Institute of Electrical Engineers (IEE)
Network Standards - cont
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- Institute of Electrical Engineers (IEE)
- Internet Engineering Task Force (IETF)
� Standards organizations are composed of delegates, from the government, academia and vendors who will be developing products based on the proposed protocols.
� The formal standards process, which is designed to ensure that a consensus is reached, is often lengthy and sometimes can take years
for approval.
Network standards� Why do we need to bother with networking standards?
- enables interoperability
- independence from vendor proprietary approaches
- enables open procurement
-Standards should be international in scope
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-Standards should be international in scope
� Important to track emerging standards
- know when it is “safe” to use them
- need to know where they come from
� Classification of computer networks
� Switched
� scale
Summary!
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� Network standards
Are there any questions?