CPSC 463 Networks and Distributed Processing

1. CPSC 463 Networks and DistributedProcessing Willis F. Marti

2. Course Overview Syllabus/policy {handout} Schedule {handout} Comments on Term Project Course Objectives ... Opinions and Facts

3. Class Admin • Test taking • Attendance & Job Searches • Sympathy

4. Project Purpose Task Network Design Approach {customer/boss/professor} Teams {preferred size is 4 or 5}

5. Science Engineering Attitude Understand what a network is, especially in the context of distributed systems Learn a good model for investigating networks Learn some network programming Identify (some) real world components How networks are built Understand there’s more than one correct solution Understand “the map is not the territory”. Course Objectives

6. Why Study Networks • When computers were rare, we studied all the new facets of computers: operating systems, languages, ... As computers became common, we added the fields that have become computer engineering. Now that computers are ubitquitous, we add the study of how best for them to communicate: networking. • A network is part of a distributed system. Part of computer science (and computer engineering) is learning how to build all the components. • What is a network? Surprisingly, few people will give you a definition that always fits. • How will we study networks? There are several methods...

7. Is this a Distributed System? Just insert a network? Mass Storage Computing (CPU) User Interface

8. Distributed System (!) This represents our definition of a distributed system, focusing on delivery of services to end users. We will explore this more after we understand more about networks. Services Servers (Storage, Compute) Network Users User Interfaces Users

9. Network Definition "A network is a collection of media, devices and protocols used to facilitate the exchange of information between computing devices in a manner relatively transparent to the end user." Contrast: The Telephone Company (TELCO) & networks.: {network as a collection of media without regard to applications}

10. Still Defining a Network • An ordered collection • of media, devices and protocols • used to facilitate the exchange of information • between computing devices • in a manner relatively transparent • to the end user."

11. Another Definition • LAN vs WAN vs MAN vs CAN ... Geography

12. Another Definition, cont. • LAN - Local Area Network • WAN - Wide Area Network • MAN - Metropolitan Area Network • CAN - A metal container

13. LAN vs MAN vs WAN • Historical Def’n {physical proximity} • Advance of Technology changes definitions • Modern Definitions Total Travel Time LAN: Data Transmission Time <= .01 to .05 Total Travel Time Data Transmission Time

14. LAN -- Key Points • Historically, LANs meant fast speed. • Fast speeds meant short(er) distances. • Therefore LANs became defined by local {short} distances • the REAL key points • Travel time about 1 to 5% of total time • LANs ‘tend’ to use broadcast protocols; WANs ‘tend’ to be point-to-point

15. Studying Networking • by protocols & programs ... • by technology ... • by components ... • Layered Models of a System! “The key to understanding networks is the idea of layered architectures.”

16. Layered Architectures-Principles- • Clearly Defined Interfaces • Separation of Functions • Peer to Peer Protocols • Provide Services Up, • Request Services Down

17. Message Message Pkts Packets Pkts Packets Layering TRANSPORT NETWORK 10010111001 10010111001 {Bits} {Bits} LINK PHYSICAL {Signal}

18. Packet Formats Data Application “Header” Presentation “Header” Data Session Header (?) Data Stream Packets Transport Header Data Network Header Data Link Header Data Framing Data

19. <some function> Protocols and Services This: or this... or this...?

20. Protocols and Services-a better model n+1 n+1 n n n-1 n-1

21. Which Architecture to Study? • TCP/IP {Internet suite} • SNA • Novell • IEEE • OSI Reference Model

22. Network Models Standards & Committees ANSI IEEE {most important for LANs} EIA ISO {does more than just data standards} ITU-T {international PTT oriented. Formerly CCITT} etc Standards & Users {cost, flexibility} Purpose of the Open Systems Interconnection Model {remember, it's just a model}

23. Using Models for Understanding Models are created by extracting key features, functions and information from a specific domain of interest so that the model contains essential attributes for understanding. Road maps are models. We extract positions of towns and cities and the roads that connect them. We ignore most terrain or reduce it to color. Road maps are good for planning trips by car but relatively useless for determining where to drill for oil. A key part of building a good model is ensuring that all features of interest are included, but only those. When using a model (network or otherwise), remember the limitation: "The map is not the territory."

24. IEEE 802 Protocols • .1 - Management • .1d - Bridge Spanning Tree • .2 - Link Layer • .3 - CSMA/CD [Ethernet] • .4 - Token Bus • .5 - Token Ring • .6 - DQDB • .7 - MAN

25. (Partial) TCP/IP Stack FTP TELNET DNS TCP UDP IP ICMP ARP DIX Ethernet or ...

26. Why the OSI Reference Model? • OSI RM is not the ISO protocol(s) • Not tied to any specific protocol suite • ‘Clean’ start • Completeness

27. Application Presentation Session Transport Network Data/Link Physical Example: OSI & the Internet NFS XDR RPC UDP IP DIX Ethernet IEEE 802.3

28. The OSI Model 7 {remember, enveloping at each layer} 6 5 4 3 2 1

29. OSI Reference Model {Each layer communicates with its peer by using the services of the layer just below, and provides services to the layer above. Only the physical layer has an actual connection}

30. OSI Model, cont {there can be multiple, separate entities at each layer} Gateway Router Bridge Repeater

31. Physical Layer • Converts Bits -> Signals & sends signals across the media • Recovers Bits from incoming Signal Key Aspects of Physical layer specifications: • Signaling Method • Connectors • Media • Voltages/Power Levels Media Considered -- Optical Fiber, Broadband Coax, baseband coax, UTP Media not Considered -- Radio/Microwave/Satellite

32. Data/Link Layer • Gets bits from A to B along a (logically) single physical link • Provides addressing and error detection. • OSI model talks about error recovery -- not usually implemented in LANs, and only in some point-to-point networks (X.25 best example) • Why no error recovery? In the case of an error in the packet, where did it come from and where was it really addressed to...

33. Data/Link Layer • Gets bits from A to B along a (logically) single physical link • Provides addressing and error detection. • OSI model talks about error recovery -- not usually implemented in LANs, and only in some point-to-point networks (X.25 best example) • Why no error recovery? In the case of an error in the packet, where did it come from and where was it really addressed to...

34. Network Layer • End-to-end packets (each system on the network has a network address BUT each packet (is)(may be) treated separately • This layer is supposed to hide all the messiness of differing link and physical layer requirements from the upper layers

35. Transport Layer • End-to-end messages Usually provides reliable, sequenced byte stream to upper layers. Does error recovery. • There are options for non-guaranteed transport

36. Session Layer • Control layer • Manages 'sessions'

37. Presentation Layer • Provides information transform services -> translation ->encryption ->compression

38. Application Layer TCP/IP ISO email SMTP X.400 file transfer FTP FTAM remote terminal/access TELNET VTS

39. Basic Network Concepts Circuit switching - {basic TELCO service. Guaranteed response because resources are guaranteed. Inefficient for some applications} Virtual-circuit packet-switching - {divide the info into packets to multiplex} Datagram packet-switching - {like the US Mail....} Connectionless vs Connection-oriented {At the Link layer, do we do acknowledgements? At the network layer,do all the packets have to follow the same route?} Multiplexing - {single media, multiple independent 'circuits'} {putting multiple 'sessions' on a single media}

40. Terminology • SAP -- Service Access Point {see Fig 1-9} • Connection Oriented • Connectionless • Datagram • Primitives

41. Modulation "Modification of a transmitted signal to encode information (bits)" ASK - Amplitude Shift Keying {varying signal strength} FSK - Frequency Shift Keying {varying signal frequency} PSK - Phase Shift Keying {don't ask!} {NB the above three methods are usually applied to signal carriers} PCM/PWM - Pulse Code Modulation/ Pulse Width Modulation {good for fiber} Others

42. Switching • Circuit Switching • Guaranteed resource • No size limit on information sent • Packet Switching - Divides the information into packets; restricts sizes; also sharing of resources • Virtual Circuit // Connect-oriented • Datagram // Connection-less

43. Multiplexing TDM - {time division multiplexing} {low overhead, inefficient} FDM - {frequency division multiplexing} STDM - { statistical time division multiplexing} {some overhead, more efficient, may FAIL}

44. Multiplexing Examples 2400 TDM 2400 A B BADCBADCBADCBAD C 9600 D STDM 2400 2400 A BACACBDCBDBABBD B C 4800 D

45. FDM

46. Multiplexing w/ Packets Like STDM, except NO "ROUND ROBIN"

47. Physical Layer Issues • Theoretical Underpinning • or, Bandwidth 101 • Media Characteristics • Optical Fiber • Coax • Copper Wire (Twisted Pair) • Wireless • Other Useful Ideas

48. Signals • Propagation - {how fast does the signal travel in that media, esp. compared to light?} • Frequency - {number of oscillations per second of the electromagnetic field of the signal} • Bandwidth - {the width/size, in Hz, of the signal -- usually defined by where most of the energy is} • Data Rate - {the number of bits per second. Distinct from, but related to, frequency and bandwidth} • Baud - {Changes per second in the signal. Limited by bandwidth.}

49. Freq/BW/DR BW Power FREQ Frequency {see Fig 2-1}

50. Maximum Data Rates • Nyquist: • DataRate <= 2*BandWidth * log2 V where ‘V’ is the number of values which are encoded into the signal. In the On/Off, 0/1 world, V = 2. Your highspeed modem has V = 16. • Shannon: • The real world is noisy, so Nyquist was an optimist. • Marti: • Complexity costs money and adds fragility. So be choosy. DR ~ 2 * BW {Max by Theory} DR ~ 1/2 * BW {Practical} <- In an On/Off world (V = 2)