1 IT Networks - Lecture 1 Mark Gleeson [email protected] 16th
March 2010 Physical Sciences in Medicine
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2 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; 4 th edition; Prentice
Hall International 2003; ISBN 0-13-066102-3, TCD Library shelf mark
500.17 N691*3
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3 What is a Computer Network? (1/2) Initially computers were
highly centralized, usually within a single room. Now lots of small
independent computers communicating to do a job. These are called
Computer Networks An interconnected collection of computers which
are: 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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4 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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5 Section 2 - Network characteristics What is a Nework?
Tanenbaums definition: "A network is an interconnected collection
of autonomous computers" IPv 4 IPv 6 AT M TCP/I P RI P OSP F ??
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7 LAN Topologies Bus architecture (Ethernet) Ring architecture
(Token Ring) Star architecture (switched Ethernet) Double ring
architecture (FDDI)
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8 Types of Networks Classification based on diameter: 1 m
System 10 mRoom 100 mBuilding 1 kmCampus 10 kmCity 100 kmCountry
1,000 kmContinent 10,000 kmPlanet Multi-processor LAN (Local Area
Networks) MAN (Metropolitan Area Networks) WAN (Wide Area Networks)
The Internet PAN (Personal Area Networks)
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9 Local-Area Networks (LANs) * Figure is courtesy of B.
Forouzan
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10 Metropolitan Area Networks (MANs) Network Cloud * Figure is
courtesy of B. Forouzan
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11 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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12 Simplex * Figure is courtesy of B. Forouzan
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13 Duplex Half-Duplex Full-Duplex * Figure is courtesy of B.
Forouzan
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14 Point-to-Point & Multipoint * Figure is courtesy of B.
Forouzan
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15 Basic Message Types Three basic message types 1. Unicast -
one sender to one receiver Sender Receiver
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16 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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17 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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18 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 and 0 Does transmission proceed simultaneously in both directions
How many pins are on connectors and what each pin does. What kind
of transmission medium, wired, fiber optic
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19 Communication between End-Systems * Figure is courtesy of B.
Forouzan
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20 Data Link Layer * Figure is courtesy of B. Forouzan
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21 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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22 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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23 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
Metcalfes Ethernet sketch
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24 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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25 Full-duplex Switched Ethernet Switch delivers packets to
individual machines No collisions One line to send One line to
transmit * Figure is courtesy of B. Forouzan
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26 Switches in Comms Rooms
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27 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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28 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 wont be a conflict Advantages No
need to install ethernet cabling everywhere Network access
everywhere in range
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29 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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30 Position of the Network Layer Sends frames through data link
layer Accepts data from transport layer
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31 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
