it networks - lecture 1 mark gleeson [email protected] (01) 896 2666 5th may 2009
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Physical Sciences in Medicine. IT Networks - Lecture 1 Mark Gleeson [email protected] (01) 896 2666 5th May 2009. Objectives. Understand some network terminology- enough to be able to read further on the topic. Understand some issues of network layout. Emphasis on practical aspects - PowerPoint PPT PresentationTRANSCRIPT
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IT Networks - Lecture 1Mark Gleeson
[email protected](01) 896 2666
5th May 2009
Physical Sciences in Medicine
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Objectives• Understand some network terminology-
enough to be able to read further on the topic.
• Understand some issues of network layout.
• Emphasis on practical aspects • Recommended Text
– Computer Networks; Andrew S. Tannenbaum; 4th edition; Prentice Hall International 2003; ISBN 0-13-066102-3, • TCD Library shelf mark 500.17 N691*3
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Section 1 – Introduction - Network Basics• Initially computers were highly
centralized, usually within a single room. Computers were physically large.
• The development and advances made in the computer industry are huge.
• Now – lots of small independent computers communicating to do a job. These are called Computer Networks
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What is a Computer Network? (1/2)• An interconnected collection of
computers which are:– Co-operative
• Co-operative action is required between the components
– Autonomous• All components are capable of independent
action• Any resource is capable of refusing requests
– Mutually Suspicious• Components verify requests
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What is a Computer Network? (2/2)• Any computer connected to a network
is known as a host.– Local host
• Your own computer– Remote host
• The computer elsewhere you are in contact with
• There are hardware and software aspects to computer networks
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Section 2 - Network characteristics• What Are Networks
• Network Types and Topologies
• Communication concepts
• Basic Message Types
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What are Networks?• Tanenbaum’s definition:
"A network is an interconnected collection of autonomous computers"
IPv4
IPv6ATM
TCP/IP
RIP
OSPF
???
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Types of Networks• Bus-based networks
– Original Ethernet (802.3)• Star-based networks
– Switched (Modern) Ethernet (802.3ab)• Ring-based networks
– FDDI– Token Ring (802.5)
• Wireless networks– WiFi (802.11a/b/g/n), Bluetooth, IrDA,
WiMax, GSM, EDGE, 3G
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LAN Topologies
Bus architecture (Ethernet) Ring architecture (Token Ring)
Star architecture (switched Ethernet)
FDDI Ring
Double ring architecture (FDDI)
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Types of Networks• Classification based on diameter:
1 m System
10 m Room
100 m Building
1 km Campus
10 km City
100 km Country
1,000 km Continent
10,000 km Planet
Multi-processor
LAN (Local Area Networks)
MAN (Metropolitan Area Networks)
WAN (Wide Area Networks)
The Internet
PAN (Personal Area Networks)
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Metropolitan Area Networks (MANs)
Network Cloud
* Figure is courtesy of B. Forouzan
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Wide-Area Networks (WANs)
• Frequently used to join companies offices worldwide together
• Latency• Administration/Jurisdiction
* Figure is courtesy of B. Forouzan
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Basic Message Types• Three basic message types
– 1. Unicast - one sender to one receiver
Sender
Receiver
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Basic Message Types• Three basic message types
– 1. Unicast - one sender and one receiver– 2. Broadcast - one sender, everybody
receives
• Broadcast addresses:– network ID +– all bits of host ID set– e.g. 134.226.255.255
Sender
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• Three basic message types– Unicast - one sender and one receive– Broadcast - one sender, everybody
receives– Multicast - one sender and a group of
receivers
Basic Message Types
Sender
Receivers
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The Physical Layer• The Physical Layer is the lowest layer and is concerned
with wiring and electrical standards. The design issues have to do with making sure that when a sender sends a 1 bit that the receiver receives a 1 bit and not a 0 bit.
• Example issues to be agreed when building this layer– How many volts to represent a 1– How many volts to represent a 0– How many microseconds a bit lasts.– Does transmission proceed simultaneously in both
directions– How are connections established and torn down– How many pins are on connectors and what each pin
does.– What kind of transmission medium, wired, fiber optic
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Duties of the Data Link Layer
The data link layer is responsible for transmitting frames from one node to the next on the same network.
* Figure is courtesy of B. Forouzan
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Packetizing & Addressing• Packetizing: Encapsulating data in
frame or cell i.e. adding header and trailer
• Addressing: Determining the address of the next hop (LANs) or the virtual circuit address (WANs)
* Figure is courtesy of B. Forouzan
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LAN Technologies - Ethernet• Developed by Metcalfe 1972/3 while at Xerox PARC
• Standards in 1978, 1995, 1998
• Types of Ethernet– Original Ethernet– Switched Ethernet– Fast Ethernet– Gigabit Ethernet
• Medium Access Control– CSMA/CD
• IEEE 802.2: Logical Link Control
Metcalfe’s Ethernet sketch
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Ethernet Addresses – The ‘MAC’ Address• A unique 48 bit long number
– Eg 00:A0:4A:21:19:13
• Types of Addresses:– Unicast – delivered to one station– Multicast – delivered to a set of stations
• 01-80-C2-00-00-00 Spanning tree (for bridges)
– Broadcast – delivered to all stations• FF-FF-FF-FF-FF-FF
vendor-specific
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Switched Ethernet
• Switch delivers packets to individual machines– Without affecting communication with
other machines• Collisions only occur on individual links
* Figure is courtesy of B. Forouzan
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Full-duplex Switched Ethernet
• No collisions– One line to send– One line to transmit
* Figure is courtesy of B. Forouzan
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Wireless (1/2)• IEEE 802.11 standard of 1997 started the
revolution with 2Mbps top speed– Now on 802.11g with 54Mbps– 802.11n to promise 150+Mbps– Referred by some as Wireless Ethernet– Shares significant similarities with original bus
style Ethernet• Reliability and Performance much less than
wired network– Current max speed 54Mbps shared by all on
same access point– Prone to interference and poor reception– Speed drops under poor conditions to reduce
errors– Range 100m+ in open much less in office
situation
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Wireless (2/2)• Star like network
– Your laptop talks to a ‘access point’ which connects to your wired network
– Laptop will move between access points to keep the strongest signal
• Uses the Industrial, Medical and Scientific Band– No licence needed– Healthcare staff should be aware of this shared
use and verify before installation that there won’t be a conflict
• Advantages– No need to install ethernet cabling everywhere– Network access everywhere in range
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The Network Layer• The Network Layer is concerned with controlling
the operation of the subnet. A key design issue is determining how packets are routed from source to destination. They can be static, dynamic.
• Example issues to be agreed when building this layer– Routing mechanisms– How is subnet congestion to be dealt with– How are costings included- national boundaries– Addressing mechanisms.– In broadcast networks the network layer may be
very thin or non-existent.
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Position of the Network Layer• Sends frames through data link layer• Accepts data from transport layer
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Duties of Network Layer
• Problems the Network Layer needs to address:– Transfer over networks of various architectures– Addressing on a “global” scale– Adjusting to maximum transmission units
• Hop-to-hop delivery provided by data link layer• Transfer of packets between end systems
provided by network layer