Transcript What are Networks? - Distributed Systems Group

Diploma in Health Informatics
Networks
Mark Gleeson
[email protected]
Distributed Systems Group,
Trinity College, Dublin
20.02.2010
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Objectives
• Understand some network terminologyenough to be able to read further on the
topic.
• Understand some issues of network design.
• Issues concerning application of networking
to health.
• Emphasis on practical aspects
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Introduction to Networks
1. Introduction
2. Network characteristics
3. Network Software
4. Network Hardware
5. Security
6. Internet and the World Wide Web
7. Telemedicine
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Section 1 – Introduction - Network Basics
• In the 20th Century developments include
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worldwide telephone networks
the invention of television and radio
the unprecedented growth of the computer
launching of communication satellites
• The convergence of computers and
communications is very significant.
• 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
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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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(Digital) Bandwidth
• The amount of data per second a
communications link can carry
• Typically referred to in bits per second
– Note 1 byte == 8 bits
• The actual amount of useful data you can
send will be less than the actual capacity
– Overheads for
• Addressing
• Routing
• Error detection
• Medium access
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Latency / Delay
• Measure of the delay from sending a piece of
data or request until it is processed at the
destination
– Exceptionally important for
• Video and audio
– Voice over IP, Skype, Video conferencing
• Interactive systems
– Inquiry based systems – patent records
– Booking systems
• Needs careful investigation to determine the
weak points
– Is it the network or the computer?
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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"
???
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, Hyperlan
IrDA, WiMax, GSM, EDGE,3G
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LAN Topologies
Bus architecture (Ethernet)
Ring architecture (Token Ring)
FDDI Ring
Star architecture (switched Ethernet)
Double ring architecture (FDDI)
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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
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Local-Area Networks (LANs)
* Figure is courtesy of B. Forouzan
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Wide-Area Networks (WANs)
• Latency
• Administration/Jurisdiction
* Figure is courtesy of B. Forouzan
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Simplex
* Figure is courtesy of B. Forouzan
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Duplex
Half-Duplex
Full-Duplex
* Figure is courtesy of B. Forouzan
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Point-to-Point & Multipoint
* 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
Sender
• Broadcast addresses:
– network ID +
– all bits of host ID set
– e.g. 134.226.255.255
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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
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Section 3 - Network Software
• Originally hardware matters were the main
focus when building networks the software
was an afterthought.
• Key Network Software concepts:
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Layers
Protocols
Interfaces
Services
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Layers
• The idea of introducing layers of software
reduces the design complexity. It divides
the large problem into smaller ones.
• The number, name, contents and function of
each layer vary from network to network.
• However for each network the idea is that
one layer offers something to a second layer
without the second layer knowing how the
first layer is implemented.
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Protocols
• Provided two networks adhere to the same
set of layers layer n on one machine can
(virtually)communicate with layer n on
another machine.
• The rules and conventions used in this
conversation are known as the layer n
protocol.
• A protocol is an agreement between the
communicating parties as to how the
communication proceeds.
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Design Issues for the layers
• Addressing – identifying senders and receivers.
• Data transfer rules- Simplex, half duplex, Full duplex.
• Error control - Agree on a protocol. Implementation of
the protocol.
• Order of the messages
• Fast sender swamping a slow receiver - feedback or an
agreed size is required.
• Length of messages - Too large/too small.
• Multiplexing - use the channel for multiple unrelated
conversations.
• Multiple routes - How to choose the route. Physical and
logical choices.
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Reference Models
• Two reference models are considered
– The OSI (Open Systems Interconnection)
Reference Model –initiated in the 1970s
matured in the late 1980s and early 1990s
– TCP/IP initiated through work carried out in
the late 1960s, matured and adopted in early
1990s
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Open Systems Interconnetion Model
•
Developed by the International Standards Organisation (ISO)
•
The model deals with connecting open systems i.e. systems that
are open for communication with other systems.
Application
Application
Presentation
Presentation
Session
Session
Transport
Transport
Network
Network
Datalink
Datalink
Physical
Physical
Medium
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Network Protocols
• Common “language” on the network
• Define network components’ interactions
– Actions/requests
– Responses
• Defined in standards
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ISO Standards
IEEE Standards (mainly at physical and mac)
ITU Recommendations
IETF Request For Comments (RFC)
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Communication between End-Systems
* Figure is courtesy of B. Forouzan
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Data Link Layer
* Figure is courtesy of B. Forouzan
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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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Medium Access Control
• Control the access to a shared medium to
prevent conflicts and collisions
– Aloha
– CSMA/CD or CSMA/CA
* Figure is courtesy of B. Forouzan
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Analogy: Point-to-Point Communication
• Simple Synchronization
Phone conversation
Alice
Bob
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Analogy: Shared Medium
• Synchronisation is more complex
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Asynchronous Systems
• Round robin
– Good if many stations have data to transmit over
extended period
• Reservation
– Good for stream traffic e.g audio, video
• Contention
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Good for bursty traffic
All stations contend for time
Distributed
Simple to implement
Efficient under moderate load
Tend to collapse under heavy load
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Multiple-Access Protocols
* 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
Metcalfe’s Ethernet sketch
• Medium Access Control
– CSMA/CD
• IEEE 802.2: Logical Link Control
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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
• 03-00-00-00-00-01
Spanning tree (for bridges)
NETBIOS
– Broadcast – delivered to all stations
• FF-FF-FF-FF-FF-FF
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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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Switches in Comms Rooms
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Wireless (1/2)
• IEEE 802.11 standard of 1997 started the revolution
with 2Mbps top speed
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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
base station
– 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 which move been access points to keep the
strongest signal
• Uses the Industrial, Medical and Scientific Band
– No licence needed
– Healthcare staff should be aware 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
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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
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Switching in the Internet
• Connection-oriented communication
– Connection exists between sender and receiver for
duration of communication
• Connection-less communication
– Data between sender and receiver
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Yet another Layer ?!?
• Transport Layer – TCP
• Why should you care?
• Applications use TCP as main communication
mechanism
– HTTP
– Remote procedure calls (RPC)
• File Transfer
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Network Layer vs Transport Layer
Network Layer
Transport Layer
• Communication between • Communication between
two nodes
processes
• Best effort delivery
• Ordered, guaranteed
delivery
• Connection-less
communication
• Connection-oriented
communication
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Transport Layer
• Process-to-Process Delivery
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IP Addresses & Port Numbers
• IP Addresses
determine the host
• Port Numbers
determine the
application
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Communication at Transport Layer
• Comms at
Transport Layer
from port to port
• IP
implementation
multiplexes
depending on
protocol field in
IP header
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Section 4 - Network Hardware
• Connecting hosts and networks require
hardware devices which include..
• Networking and Internetworking Devices
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Repeaters
Bridges
Hubs
Switches
Routers
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Networking and Internetworking Devices
• These devices can be divided into 3
categories
– Repeaters,
– Bridges,
– Routers and Gateways.
• Repeaters and Bridges are used at the
Networking of hosts
• Routers and Gateways are used for
Internetworking
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Repeaters and Bridges
• Repeaters
– Operate at the physical layer. They
regenerate signals.
• Bridges
– Operate at the physical and data link layers.
– They are used to divide a network into
segments and can control traffic flow and
are useful for securing the network.
– They can also regenerate signals.
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What is a Switch
• A layer 2 device – Data Link Layer
• Builds a table of the MAC addresses of devices
attached on each port
• ‘Store and Forward’
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Switch receives a packet
Verifies it is error free
Looks at its destination MAC
Sends the packet on
• ‘Cut Through’
Photo thanks to Cisco Systems
– Starts to forward packet once it reads the
destination address
– No error checking
• Improved performance
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What is a Router
• A layer 3 device –
– Works at physical, data link and network layers e.g.
Internet Protocol (IP) level
– Is a bridge between a number of distinct networks
• Example your internal network and the internet beyond
• Range from simple devices
• ADSL router for home users
– To
• Extremely complex enterprise level
• Looks at the destination of each IP packet and
determines where it would be sent on for its next
hop
– Tries to select the best route
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Example Sizes of Medical Images
Scan Type
General Radiographs
Ultrasound
Doppler Ultrasound
Bariums
ERCP's
CT
MRI
Nuclear Medicine
Cardiac Angios
Daily Totals
Yearly Totals
Number of Exams per
day
200
20
30
5
5
12
10
10
10
Total (MB)
9600
60
90
400
400
1800
1500
30
8000
302
78,520
21,880
5,688,800
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Uses of Networks in Healthcare?
• Communicating into/out of and between
hospitals
• Paging Staff
• Networking instrumentation
• Maintenance of instrumentation
• To aid communication
– Professional to professional.
– Professional to patient.
– Patient to patient.
• Sharing Information of all types
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Section 5 - Security
• Secrecy
– Keeping information out of the hands of
unauthorised users.
• Authentication
– Making sure you are talking to the right
person.
• Data Integrity control
– Making sure the data is correct.
• Security effects each layer in the network
design.
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No Network Is Secure
• Original Ethernet
– Every host on the bus could see and capture every
transmission made
• The physical network itself cannot be considered to
be secure
– Wires can be tapped
• Wireless communications available to all within
range with a suitable receiver
• Need to trade off the strength of security with the
practicality of the measures
– Users when faced with a complex process may
attempt to undermine the system
• Sharing of passwords or not logging out
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Wireless Networks
• Extremely vulnerable to attack
– Anyone with a suitable radio can listen
• IEEE 802.11 originally used a 40 bit WEP key
– Shared encryption key by all users of the
network
– Later versions supported a 104 bit key
– Proved to be very easy to crack in both versions
•
WiFi Protected Access (WPA/WPA2)
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Based on 802.11i standard
EAP extensible Authentication Protocol
» Authentication framework not a protocol
» Can integrate with existing authentication systems
» 802.1x
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• Best practice in Network Management is to
heavily restrict access to external users or
to block it totally
– Avoid potential security issues
– Protect from hackers
• What of legitimate users
– People who work at other locations
– Particularly relevant concerns in the
Healthcare Domain
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VPN – Virtual Private Network
• Not strictly a security solution
• Two implementations
– Connecting you to a remote network
– A network within a network
• Allows you to access resources on another
network as if you where connected directly
• A secure encrypted tunnel between your
computer and others on the same network
• Typically requires a dedicated ‘VPN box’ on the
office end network to provide the service
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VPN - Connecting you to a remote network
• Ideal for a single user
– Work from home, on the road, other
institution
• User needs VPN client software
– Setup can be complex for users
– Need to implicitly log in to access the
network
• Not transparent
– Potential security risk if users computer is
breeched
• Hacker may have access into network
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Methods of Attack (1/3)
• Impersonation
– Using someone else’s password or a terminal that is
already logged on.
• Active wire-tapping
– Connecting a device(authorised/unauthorised) to a
communication link to obtain access to data through the
generation of false messages.
• Passive wire-tapping
– Monitoring data coming over a communication link.
• Traffic flow analysis
– Analysing the frequency of data traffic, seeing which data
is encrypted and which is not.
• Eavesdropping
– interception of information
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Methods of Attack (2/3)
• Replay
– Play back a recording of a communication
• Routing Table modification
– Sending messages to the wrong address or multiple
addresses.
• Audit Trail Information Modification
– To cover up an attack.
• Operational Staff Table Modification
– To change access rights.
• Bogus Frame insert
– Inserting bogus information as a frame.
• Data Portion Modification
– Modify the data portion of a message.
• Viruses
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Methods of Attack (3/3)
• Sequencing Information Modification
– Change the order of the pieces of information.
• Message Deletion
– Removing the message completely
• Protocol Control Information modification
– To send data to a different location.
• Misuse of resources
– Swamping communication lines – Denial of service
• Interruption of power supply
– Denial of service
• Malicious physical damage
– Denial of service
• Theft
– Parts of computers or entire computers could be stolen.
Confidentiality issues arise.
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Disposal of computer hardware
• You typically contract a third party to securely
shred paperwork, but you skip a used computer.
– Computer can store a virtually unlimited amount of
data in a easy to search format
• Serious privacy issues concerning medical records
• Computer may have no confidential information
but!
– Usernames, passwords, security certificates and so
on for networked information may be stored on the
computer, thus allowing access
• Essential the contents of the hard disk be wiped
not just deleted
– Most operating systems have the ability to do this
– Or remove hard drive and use a sledgehammer
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Section 6 - The Internet and the World Wide Web
• Addressing and Domain Names
• Who is in charge
• Relationship between IP address and
hostnames
• Arrangements for .ie domains
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Internet Addressing and Domain Names
• To be able to identify a host on the
internetwork, each host is assigned an address
– Internet Protocol address.
• Addresses are assigned in a delegated manner.
• The Internet Corporation for Assigned Names
and Numbers (ICANN) has responsibility for
Internet Protocol (IP) address space allocation
• ICANN are the top body. They comprise IANA
http://www.iana.org/
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Internet Addressing and Domain Names
• Users are assigned IP addresses by Internet service
providers (ISPs). ISPs obtain allocations of IP
addresses from a local Internet registry (LIR) or
national Internet registry (NIR), or from their
appropriate Regional Internet Registry (RIR):
– APNIC (Asia Pacific Network Information Centre) Asia/Pacific Region
– ARIN (American Registry for Internet Numbers) North America and Sub-Sahara Africa
– LACNIC (Regional Latin-American and Caribbean IP
Address Registry) – Latin America and some
Caribbean Islands
– RIPE NCC (Réseaux IP Européens) - Europe, the
Middle East, Central Asia, and African countries
located north of the equator
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Internet Addressing and Domain Names
• The .org domain is operated by Public Interest
Registry. It is intended to serve the non
commercial community, but all are eligible to
register within .org.
• The .com domain is intended to serve the
commercial community.
• The .gov domain is reserved exclusively for the
United States Government. It is operated by the US
General Services Administration.
• The .edu domain is reserved for postsecondary
institutions accredited by an agency on the U.S.
Department of Education's list of Nationally
Recognized Accrediting Agencies and is registered
only through Educause.
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IP and Internet Addressing
• Currently there are two types of Internet
Protocol (IP) addresses in active use:
– IP version 4 (IPv4) and IP version 6 (IPv6).
• IPv4 is still the most commonly used version.
• IPv4 addresses are 32-bit numbers often
expressed as 4 octets in "dotted decimal"
notation (for example, 192.0.32.67).
• Deployment of the IPv6 protocol began in 1999.
IPv6 addresses are 128-bit numbers and are
conventionally expressed using hexadecimal
strings (for example,
1080:0:0:0:8:800:200C:417A).
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IP Addresses
• 32-bit number in IPv4
– 4,294,967,296 addresses
• IP addresses are unique and universal
– with some exceptions
• Dotted decimal notation:
– Bytes of binary notation represented as
decimal separated by dot
• Internet hosts have both IP addresses and
hostnames
– wilde.cs.tcd.ie == 134.226.32.55
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Mapping Domain Names
– Hostname
- wilde.cs.tcd.ie
– Internet Address - 134.226.32.55
• How does a machine translate a fully
qualified hostname into an IP address?
• It consults its nearest Domain Name Server
(DNS)
• The local Nameserver knows the mappings
for local machines and
– At least one root nameserver which knows all
nameservers for the top level domains.
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.ie domains
• All registrations handled by the IE Domain
Registry - www.iedr.ie
– Was based in UCD until 2000, now a
independent non profit making body
– You are required to prove a connection to
the domain name sought
• 4th Feb 2010
– Total number of domains 137,661
• In Jan 1995
– Total domains 347
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Section 7 – Telemedicine
• Telemedicine is the rapid access to shared and
remote medical expertise by means of
telecommunications and information
technologies, no matter where the patient or
the relevant information is located. (CEC 1993)
• Telemedicine has been defined in General
Terms as “Medicine practiced at a distance”
and as such, it encompasses both diagnosis and
treatment, as well as medical education.
(Journal of Telemedicine and Telecare, 1995)
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Definitions
• Telemedicine is the delivery of healthcare
services, where distance is a critical factor, by
all healthcare professionals using information
and communications technologies for the
exchange of valid information for diagnosis,
treatment and prevention of disease and
injuries, research and evaluation, and for the
continuing education of healthcare providers,
all in the interests of advancing the health of
individuals and their communities. (World
Health Organisation 1998)
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Telemedicine
• Many different definitions of Telemedicine. Be
aware of this.
• Telemedicine is a process not a technology. Can
be applied to many different domains.
• Can be used for patient/clinician,
patient/patient, clinician/clinician
communication.
• Can be used to support training
• As with all applications of technology,
appropriateness is the key. The application
should be clinically driven.
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Characteristics of Telemedicine systems
• Interaction style- Real Time, Store and
Forward.
• Data types- Text, Images, Sound, Video
• Equipment
• Action – Direct Intervention, Advice
• Patient numbers – one patient, multiple
patients
• Duration
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Some Advantages and Obstacles of
Telemedicine
• Advantages
– Improved use of resources
– Continuing professional
development
– Reduces unnecessary
patient transfers
– Facilitates homecare for
the elderly and the
chronically ill
– Equitable access to care!
– Links doctors with remote
centres of excellence
– Wireless links can be used
in cases of lack of
infrastructure
• Obstacles
– Patient and
professional
dissatisfaction in some
specialities
– Lack of standards
– Security issues
– Legal and ethical
implications
– Equipment failure
– Lack of protocols of
care for these new
types of interactions.
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History
• Pre-electronic telemedicine
– Accounts from the middle ages of a physician examining a
patient for plague- the patient and the physician were on
opposite sides of the river.
– Prescribing by post was practised well before national
postal systems were in place.
• Electronic telemedicine
– Telegraphy- equipment was developed to send an X-ray
– Telephony- voice communication, computer networks
– Radio- initially by morse code and later by voice.
– Television- closed circuit television, video conferencing
– Wireless communication- use of mobile phone
technologies and satellites.
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Research
• Why is Telemedicine not in widespread use?
• The technologies exist but the organisational
and personal problems exist.
• Lots of funding has been allocated and has been
spent on projects analysing, testing and
evaluating technical requirements.
• More projects/research should be funded to
show cost-effectiveness and evaluation of new
Telemedicine applications.
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Ethical and Legal Issues
• Some projects in Europe have looked at certain
aspects of this area (SEISMED, ISHTAR,
TrustHealth and SIREN). They have mainly been
concerned with the security and
confidentiality.
• More work needs to be done to research other
aspects including accountability, responsibility,
licensure, reimbursement, intellectual property
rights, changes in consultation and referral
patterns, defining the ‘owner of patients’,
defining geographical catchment areas.
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Economics/Evaluation
• Need to compare the new technology with an
alternative way of working. What is the system
costing at the moment?
• How to asses the cost of the new technologyequipment, software, installation, training,
maintenance, legal, utilisation rates.
• How do we asses the benefits- people getting well,
shorter stays in hospital, less time spent with the
expert, patient not having to travel, expertise
experienced by the remote healthcare
professional.
• Methods are required if economic evaluation is to
take place. Care should be taken when comparing
costs across, domains, environments and time.
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Practice
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Teleradiology
Telepathology
Teledermatology
Telecardiology
Telepsychiatry
Teleorthopaedics
Surgical Consultations
TeleENT
Tele-EEG
Minor Injuries
• Mobile Telemedicine
• Maritime
Telemedicine
• Teleopthamology
• Home Care
• Telephone Services
• Education
• Telesurgery
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Using Networks to Provide Equality of
Care?
• Network Infrastructures- Network hardware
and network software
• Network users
• Software applications
• Legislation
• Standards
• Delivering care (need experts on site)
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Network Infrastructure
• In order to avail of networked healthcare a
network infrastructure must be in place.
• This infrastructure requires an initial
investment, maintenance investment and
investment to keep it up to date
• It is hard to see therefore even at the
technology end how equality of care can be
achieved.
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Network Users
• In various countries, regions and hospitals
different levels of technical skill exist.
• If we assume that all places have the same
network infrastructure it still doesn’t allow
us achieve equality of care
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Software applications
• On top of the network infrastructure
software applications.
• Depending on economics, skill and
awareness of users differences can exist.
• Not everyone will be aware of the software
applications that exist and the implications
of choosing particular software e.g. from
standards point of view
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Legislation
• Be aware that using networks allows the
user to bypass physical boundaries thus
enabling a specialist in Ireland to
communicate with a patient in England.
There are legal implications to this that
haven’t been addressed.
• Equality of care may not be possible due to
these legalities. The closer you live to the
specialist the better.
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Standards
• In order to have healthcare delivered to all
areas standards are required.
• Communication standards
• Coding standards e.g. for diagnosing,
prescribing.
• Data set format standards
• Semantic standards
• If all areas do not agree to the standards
then equality of care is not possible.
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Experts on site
• Even if all the infrastructure, software
applications, standards, legislation and skills
are equal is it possible to get equality of
care?
• Remember healthcare is ultimately
delivered by human experts.
• Technology can only be used to support the
current processes of healthcare delivery or
to make new processes possible.
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