Transcript physcial_sci_networks_part1

Physical Sciences in Medicine
IT Networks - Lecture 1
Mark Gleeson
[email protected]
16th March 2010
1
Objectives
• Understand some network terminologyenough 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
2
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
3
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
4
Section 2 - Network characteristics
• What is a Nework?
– Tanenbaum’s definition:
"A network is an interconnected collection
of autonomous computers"
??
? OSP
F
5
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
6
LAN Topologies
Bus architecture (Ethernet)
Ring architecture (Token Ring)
FDDI Ring
Star architecture (switched Ethernet)
Double ring architecture (FDDI)
7
Types of Networks
• Classification based on diameter:
1 m System
10 m Room
Multi-processor
PAN (Personal Area Networks)
100 m Building
1 km Campus
10 km City
LAN (Local Area Networks)
MAN (Metropolitan Area Networks)
100 km Country
WAN (Wide Area Networks)
1,000 km Continent
10,000 km Planet
The Internet
8
Local-Area Networks (LANs)
* Figure is courtesy of B. Forouzan
9
Metropolitan Area Networks (MANs)
Network Cloud
* Figure is courtesy of B. Forouzan
10
Wide-Area Networks (WANs)
• Frequently used to join companies offices
worldwide together
• Latency
• Administration/Jurisdiction
* Figure is courtesy of B. Forouzan
11
Simplex
* Figure is courtesy of B. Forouzan
12
Duplex
Half-Duplex
Full-Duplex
* Figure is courtesy of B. Forouzan
13
Point-to-Point & Multipoint
* Figure is courtesy of B. Forouzan
14
Basic Message Types
• Three basic message types
– 1. Unicast - one sender to one receiver
Sender
Receiver
15
Basic Message Types
• Three basic message types
– 1. Unicast - one sender and one receiver
– 2. Broadcast - one sender, everybody
receives
Sender
• Broadcast addresses:
– network ID +
– all bits of host ID set
– e.g. 134.226.255.255
16
Basic Message Types
• Three basic message types
– Unicast - one sender and one receive
– Broadcast - one sender, everybody receives
– Multicast - one sender and a group of
Sender
receivers
Receivers
17
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
18
Communication between End-Systems
* Figure is courtesy of B. Forouzan
19
Data Link Layer
* Figure is courtesy of B. Forouzan
20
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
21
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
22
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
Metcalfe’s Ethernet sketch
• Medium Access Control
– CSMA/CD
• IEEE 802.2: Logical Link Control
23
Ethernet Addresses – The ‘MAC’
Address
• A unique 48 bit long number
– Eg 00:A0:4A:21:19:13
vendor-specific
• 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
24
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
25
Switches in Comms Rooms
26
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
27
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
28
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.
29
Position of the Network Layer
• Sends frames through data link layer
• Accepts data from transport layer
30
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
31