1. CS551 Distributed Operating Systems Colorado State University at Lockheed-Martin Lecture 1 -- Spring 2001

2. 24 January 2001CS-551, Lecture 12 CS551: Lecture 1 n Topics – Introduction; Syllabus; G-25 Forms n Homework; Reading Reports; Project – Galli: Chapters 1, 2, 3, 4, 5, 7, 8 (maybe), 10 n Some networking topics included in course – What is a distributed system? A network? – What is a protocol? n ISO OSI Protocol n TCP/IP

3. 24 January 2001CS-551, Lecture 13 What is a distributed system? n A collection of independent computers n A communication facility to pass messages n No shared memory n No shared clock n Each computer has its own operating system

4. 24 January 2001CS-551, Lecture 14 Why have distributed systems? n Price / Performance n Resource sharing n Faster response time n Improved reliability n Modular expandability

5. 24 January 2001CS-551, Lecture 15 Distributed system organizations n Microcomputer model – several multiuser systems n Workstations/PCs model – each user has own WS/PC to do work – each user shares files and other resources n Processor pool model n LANs, MANs, WANs, WWW

6. 24 January 2001CS-551, Lecture 16 Figure 1.1 Computers in a Networked Environment. (Galli, p. 3)

7. 24 January 2001CS-551, Lecture 17 Figure 1.2 Connecting LAN Subnets with a Backbone. (Galli, p.6)

8. 24 January 2001CS-551, Lecture 18 Figure 1.3 Common Wired LAN Topologies. (Galli, p.7)

9. 24 January 2001CS-551, Lecture 19 Distributed Operating Systems n Appears to users as a single system on a single machine n A virtual uniprocessor n Users do not know where files are located n Users don’t know where jobs are executed

10. 24 January 2001CS-551, Lecture 110 Issues in Distributed O.S. – Global Knowledge – Naming – Scalability – Compatibility – Process synchronization – Resource management – Security – Structuring

11. 24 January 2001CS-551, Lecture 111 Issues: Global Knowledge n Unable to determine up-to-date global state – no global memory – no common clock – unpredictable message delays n Need device-efficient distributed control – e.g. how to get a concensus n Need method for ordering events

12. 24 January 2001CS-551, Lecture 112 Issues: Naming n All objects are named n Need to map name onto its location n Need a directory (or directories) – replicated (to maintain consistency) – versus – partitioned (which partition helps me?)

13. 24 January 2001CS-551, Lecture 113 Issues: Scalability, Process Synch n Scalability – Can system grow without performance degradation? – Want to avoid centralized components n Process synchronization – Enforce mutual exclusion to shared resources – Deal with potential for deadlock

14. 24 January 2001CS-551, Lecture 114 Issues: Compatibility n Possible at different levels n Binary level: all processing elements run same binary code n Execution level: same source code can be compiled and run on all nodes n Protocol level: all processing elements support same protocols

15. 24 January 2001CS-551, Lecture 115 Issues: Resource management n Data migration: bring data to the location – distributed file system – distributed shared memory n Computation migration – e.g. RPC – e.g. send a query for info computed remotely instead of requesting raw data n Distributed scheduling – process migration

16. 24 January 2001CS-551, Lecture 116 Issues: Security n Authentication – verify user identification n Authorization – determine user privileges

17. 24 January 2001CS-551, Lecture 117 Issues: Structuring n Monolithic kernel – each node doesn’t need entire kernel n Collective kernel – O.S. services are processes – microkernel supports messages between such processes n Object-oriented – O.S. services are a collection of objects

18. 24 January 2001CS-551, Lecture 118 Client-Server vs. Peer-To-Peer n Client-Server – Similar to collective kernel distributed O.S. – Servers respond to requests from clients n Peer-to-Peer – An extension of client/server model – A many-to-many relationship between nodes

19. 24 January 2001CS-551, Lecture 119 Figure 1.6 Client/Server Model. (Galli, p.13)

20. 24 January 2001CS-551, Lecture 120 Figure 1.7 Peer-to-Peer Model. (Galli, p.14)

21. 24 January 2001CS-551, Lecture 121 What is a network? n A form of a distributed system n Connected nodes may be homogeneous or heterogeneous n Nodes may be some distance apart n A network may consist of other networks n LANs, MANs, WANs n The Internet is a WAN: the WWW

22. 24 January 2001CS-551, Lecture 122 Layered Network Models n Used to describe network functions n Used to reduce network complexity n Each layer logically communicates with the corresponding layer on the remote host n Messages – enveloped while passed down through the local host layers – stripped down to original message while passed up through remote host layers

23. 24 January 2001CS-551, Lecture 123 Networks: Layered Models Application Layer O.S. Layer Application Layer Interconnect Layer O.S. Layer Interconnect Layer virtual path physical path

24. 24 January 2001CS-551, Lecture 124 What is a protocol? n A set of rules n A method for – establishing a connection between two sites – sending a communication over the connection – acknowledging receipt of message – terminating the connection n Example: a telephone call n Examples: ISO/OSI; TCP/IP; UDP; SMTP

25. 24 January 2001CS-551, Lecture 125 ISO / OSI Protocol n Probably most popular network protocol model n Implementation often takes efficiency- related shortcuts n Includes seven layers, grouped into 3 types – application – operating system – communication service

26. 24 January 2001CS-551, Lecture 126 OSI / ISO Layers n Application – Application layer -- user programs – Presentation layer -- common data transformations n Operating system – Session layer -- process-to-process communication – Transport layer -- reliable host-to-host communication

27. 24 January 2001CS-551, Lecture 127 ISO / OSI Layers, continued n Communication service – Network layer -- packets, routing – Data Link layer -- reliability, flow control – Physical layer -- hardware to move a bit stream between nodes – Needed by any network node, even a store-and- forward node – May exist partly as hardware

28. 24 January 2001CS-551, Lecture 128 Figure 1.4 The ISO/OSI Reference Model. (Galli, p. 9)

29. 24 January 2001CS-551, Lecture 129 ISO/OSI Layers: Application n Miscellaneous applications – FTP (file transfer protocol) – remote login: rlogin – browsers: Netscape, Internet Explorer – email (via SMTP) – RJE (remote job entry)

30. 24 January 2001CS-551, Lecture 130 ISO/OSI Layers: Presentation n Common data transformations – data compression – encryption – big/little Endian

31. 24 January 2001CS-551, Lecture 131 ISO/OSI Layers: Session n Process-to-Process Communication – buffering n Some synchronization – synchronous data communication

32. 24 January 2001CS-551, Lecture 132 ISO/OSI Layers: Transport n Reliable site-to-site communication

33. 24 January 2001CS-551, Lecture 133 ISO/OSI Layers: Network n Logical path for communication – converts frames --> packets --> frames – X.25 connection-oriented – IP connectionless – used for WANs; redundant for LANs

34. 24 January 2001CS-551, Lecture 134 ISO/OSI Layers: Data Link n Reliable data transmission – message goes out in frames n character count -- header specifies length n character stuffing -- special character at end n bit stuffing -- special bit sequence at end – on LANs can put out a special synch signal – adds a checksum to trailer to detect errors

35. 24 January 2001CS-551, Lecture 135 ISO/OSI Layers: Data Link, cont. n Flow control – synchronizes message passing activity – stop-and-wait -- sender waits for receiver’s permission (inefficient for large transmissions) – sliding window -- allows several outstanding unacknowledged frames (needs sequence #s) – HDLC (high level data link control) -- balanced, permits two-way simultaneous message passing, acknowledgments in frame headers, errors results in resend requests

36. 24 January 2001CS-551, Lecture 136 ISO/OSI Layers: Physical n Raw bit-stream communication – circuit switching n reserves a fixed communication at start n releases path at end n best for long, continuous stream – packet switching n demands access when ready to send packet of info n packet may contain 10 - 1000 bytes n may need several packets n best for bursty, short communication

37. 24 January 2001CS-551, Lecture 137 Figure 1.5 TCP/IP Relationship to ISO/OSI Reference Model. (Galli, p. 12)