IT Networks - Lecture 1 Mark Gleeson gleesoma@csd.ie (01) 896 2666 5th May 2009

1. Physical Sciences in Medicine IT Networks - Lecture 1 Mark Gleeson gleesoma@cs.tcd.ie (01) 896 2666 5th May 2009

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; 4th edition; Prentice Hall International 2003; ISBN 0-13-066102-3, • TCD Library shelf mark 500.17 N691*3

3. Section 1 – Introduction - Network Basics • 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

4. 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

5. 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

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

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

8. 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

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

10. 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

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

12. Metropolitan Area Networks (MANs) Network Cloud * Figure is courtesy of B. Forouzan

13. Wide-Area Networks (WANs) • Frequently used to join companies offices worldwide together • Latency • Administration/Jurisdiction * Figure is courtesy of B. Forouzan

14. Simplex * Figure is courtesy of B. Forouzan

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

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

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

18. 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

19. 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

20. 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

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

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

23. 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

24. 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

25. 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

26. 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

27. Switched Ethernet • Switch delivers packets to individual machines • Without affecting communication with other machines • Collisions only occur on individual links * Figure is courtesy of B. Forouzan

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

29. Switches in Comms Rooms

30. 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

31. 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

32. 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.

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

34. 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