Mark Gleeson gleesoma@csd.ie (01) 896 2666 Distributed Systems Group, Trinity College, Dublin

1. Diploma in Health Informatics Networks Mark Gleeson gleesoma@cs.tcd.ie (01) 896 2666 Distributed Systems Group, Trinity College, Dublin 14.02.2009

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. Introduction (1/2) • In the 20th Century key technologies were employed for information gathering, processing and distribution. • Some developments include • worldwide telephone networks • the invention of television and radio • the unprecedented growth of the computer industry • launching of communication satellites • These areas are converging. The convergence of computers and communications is very significant.

6. Introduction (2/2) • 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

7. 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

8. 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

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 • 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. Interfaces • Interfaces exist between adjacent layers. • The interface specifies what one layer is offering to the other layer. • Analogous to Object-Oriented concept of Encapsulation • One of the most important aspects of designing the network software is to provide clean, well understood interfaces. Minimise the amount of information that has to be passed from layer to layer. • Once a layer’s interface is defined many implementations of that layer can exist. The only stipulation is that the interface is adhered to.

29. 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.

30. 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

31. 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.

32. Principles used to arrive at the Seven Layer Architecture • A layer should be created where a different level of abstraction is needed. • Each layer should perform a well defined function • Standardisation issues. • Minimise data that has to travel between the layers • Large enough number of layers to support distinct functionality but not too large a number to create an unwieldy architecture

33. 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)

34. The TCP/IP Reference model • The grandparent of all computer networks the Arpanet – research network sponsored by the Department of Defence (DoD) in America. • The network used leased lines to connect government offices and universities together. When satellite and radio networks appeared there were problems. The thinking for TCP/IP began. TCP/IP is named after its two primary protocols. • TCP- Transmission Control Protocol • IP- Internet Protocol • A layered architecture used to connect multiple networks together in a seamless way was one of the design goals from the very beginning • Connections should remain intact even if there was some subnet damage.

35. 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

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

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

38. 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

39. 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

40. Error Control & Flow Control • Error Control: Detect errors in received data and attempt to correct them • Error Detection • Error Correction • Flow Control: Prevent the sender from overwhelming the receiver • Go-back-N • Sliding Window

41. 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

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

43. Analogy: Shared Medium • Synchronisation is more complex

44. 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

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

46. 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

47. LAN Technologies - Evolution of Ethernet • 1972/73 defined for coaxial cable • Fast Ethernet used mainly unshielded twisted pair (UTP) • Gigabit Ethernet now common in desktops and laptops • 10GB Ethernet used mainly for backbone

48. 802.3 MAC Frame • 64-bit frame preamble (10101010) used to synchronize reception • 7 bit preamble (10101010) + 1 start flag (10101011) • Maximum frame length: 1518 bytes  max 1500 bytes payload • Minimum frame length: 64 bytes  min 46 bytes payload * Figure is courtesy of B. Forouzan

49. 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

50. Non-bridged and Bridged Networks • Extension of Networks: • Repeaters, Hubs - Physical Layer • Bridges, Switches - Data Link Layer • Routers - Network Layer • Collision domains: • Collision affects all machines in one segment * Figure is courtesy of B. Forouzan