Dr Mark Gleeson gleesoma@tcd.ie National Digtial Research Centre &

1. Diploma in Health Informatics Networks Dr Mark Gleeson gleesoma@tcd.ie National Digtial Research Centre & Distributed Systems Group, Trinity College Dublin 18.02.2011

2. Objectives • Understand some network terminology- enough 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

3. Introduction to Networks • Introduction • Network characteristics • Network Software • Network Hardware • Security • Internet and the World Wide Web • Telemedicine

4. Section 1 – Introduction - Network Basics • What is a network? • What does it do? • How useful is the network • Various key attributes

5. Section 1 – Introduction - Network Basics • In the 20th Century developments include • 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

6. 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

7. 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

8. Importance of the Network • The Network Is The Computer! • John Gage - Sun Microsystems • The network is the enabler • Metcalfe's law • The value of a telecommunications network is proportional to the square of the number of users of the system (n^2). • In simple terms you need critical mass to get value from the network • This explains the rise of social networking • Facebook & Twitter

9. (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 • 1 byte = 1 alphanumeric character • The actual amount of useful data you can send will be less than the actual capacity • Overheads for • Addressing • Routing • Error detection • Medium access

10. 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?

11. More Terminology • Attenuation • Measure of how much a signal degrades per distance in a certain medium • Different cable types have difference values • Attenuation limits the distance you can communicate over • Electro Magnetic Interference - EMI • Electrical noise artificially generated • Watch out for high powered electrical equipment • MRI machines, Trams, Electric trains, Microwaves • Of particular concern in wireless networks • Microwaves operate at a frequency used by 802.11b/g

12. Section 2 - Network characteristics • What Are Networks • Network Types and Topologies • Communication concepts • Basic Message Types

13. What are Networks? IPv4 TCP/IP ??? RIP ATM IPv6 OSPF • Tanenbaum’s definition: "A network is an interconnected collection of autonomous computers"

14. 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

15. LAN Topologies Bus architecture (Ethernet) Ring architecture (Token Ring) Star architecture (switched Ethernet) Double ring architecture (FDDI)

16. Types of Networks • Classification based on diameter: Multi-processor PAN (Personal Area Networks) LAN (Local Area Networks) MAN (Metropolitan Area Networks) WAN (Wide Area Networks) The Internet

17. Local-Area Networks (LANs) * Figure is courtesy of B. Forouzan

18. Wide-Area Networks (WANs) • Latency • Administration/Jurisdiction * Figure is courtesy of B. Forouzan

19. Simplex * Figure is courtesy of B. Forouzan

20. Duplex Half-Duplex Full-Duplex * Figure is courtesy of B. Forouzan

21. Point-to-Point & Multipoint * Figure is courtesy of B. Forouzan

22. Basic Message Types • Three basic message types • 1. Unicast - one sender to one receiver Sender Receiver

23. 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

24. 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 receivers Sender Receivers

25. Section 3 - Network Software • Originally hardware matters were the main focus when building networks the software was an afterthought. • Key Network Software concepts: • Layers • Protocols • Interfaces • Services

26. 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.

27. 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.

28. 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.

29. 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

30. 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.

31. Network Protocols • Common “language” on the network • Define network components’ interactions • Actions/requests • Responses • Defined in standards • ISO Standards • IEEE Standards (mainly at physical and mac) • ITU Recommendations • IETF Request For Comments (RFC)

32. Communication between End-Systems * Figure is courtesy of B. Forouzan

33. Data Link Layer * Figure is courtesy of B. Forouzan

34. 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

35. 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

36. 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

37. Analogy: Point-to-Point Communication Alice Bob • Simple Synchronization Phone conversation

38. Analogy: Shared Medium • Synchronisation is more complex

39. 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 • Good for bursty traffic • All stations contend for time • Distributed • Simple to implement • Efficient under moderate load • Tend to collapse under heavy load

40. Multiple-Access Protocols * Figure is courtesy of B. Forouzan

41. 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

42. 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) • 03-00-00-00-00-01 NETBIOS • Broadcast – delivered to all stations • FF-FF-FF-FF-FF-FF vendor-specific

43. Full-duplex Switched Ethernet • No collisions • One line to send • One line to transmit * Figure is courtesy of B. Forouzan

44. Switches in Comms Rooms

45. 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 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

46. 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

47. 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.

48. Position of the Network Layer • Sends frames through data link layer • Accepts data from transport layer

49. 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

50. 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