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CS4/MSc Distributed Systems

Important

All students should have received their marks for the coursework by now.

Basic Information

This module runs in the first semester, on Monday and Thursday at 15:10 - 16:00, taught by Allan Clark. Lectures will take place in the Lecture Theatre in the Hugh Robson Building.

Lecture Slides

Below are the slides for each of the parts of the course individually but you can save yourself some time and download them all together as a single file by clicking: HERE

1. Course Information
2. Introductory Material
3. Fundamental Concepts
4. Time and Global States
5. Coordination and Agreement
6. Distribution and Operating Systems
7. Peer-to-Peer Systems
8. Security
9. Summary

Related Reading

• Interesting blog post on debugging a distributed system
• Peerson a peer-to-peer social networking site
• Breaking a poker site (from 1999 but still relevant)
• Article on encryption and cloud computing

Clarifications

Any student queries which I believe will be of general use to the class I will place here (with perhaps a useful answer). If you have a question of your own email me a.d.clark@ edinburgh, academic, uk (ed.ac.uk)

• Q. Can I just make sure that the exam will take place at the end of semester two?
  A. Yes the exam will be in the exam diet of semester 2 in April/May, you can check this for this course and your other courses by looking at the drps page for the course. For distributed systems level 10 this is: here and for level 11 this is: here See on the left hand side, under "Course Delivery Information" and then "Exam Diet". For your other courses you can search the DPTs here

Course Description

A distributed system is broadly categorised as a collection or network of loosely coupled, autonomous computers that can communicate with each other and execute logically separate computations, though these may be related to concurrent computations on other nodes.

• The nodes are relatively loosely coupled.
• Each node is a self-contained autonomous computer with its own peripherals.
• The system can survive various categories of node and network failures.
• The nodes may execute logically separate computations, though these may be related to concurrent computations on other nodes.
• The system is asynchronous.

Distributed systems have become pervasive---many applications now require the cooperation of two or more computers--yet the design and implementation of such systems remain challenging and complex tasks. Difficulties arise from the concurrency of components, the lack of a global clock and the possibility of independent failure of components. Moreover designs must aim to provide inter-operability, transparency and autonomy. The emphasis of this module is on gaining understanding of the principles and concepts that are used to design distributed systems and experience of software platforms which underpin their development.

Coursework

• The course work assignment for Level 10 students is here
• The course work assignment for Level 11 students is here

The lecture slides used to assign the coursework are available here

• Three will be a course work assignment given out for both level 10 and level 11 students on Monday October 8th.
• The deadline for level 10 students will be 4pm Thursday November 8th
• The deadline for level 11 students will be 4pm Thursday November 22nd

Submission

Submission will be made using the submit command:

• For Level 10 students
  submit ds 1 < filename >
• For Level 11 students
  submit ds 2 < filename >

The < filename > can be a directory or a single file.

Clarifications

• Q. I have found a topology in which, after a link failure, the algorithm does not converge to the optimal routes
  A. That is fine, that's a known problem and to be expected, write up your findings in your submission.
• Q. I can even get the algorithm itself to loop indefinitely
  A. Excellent, write up what you have found in your submission
• Q. In the handout you say that we can avoid doing the text parsing and you give the following syntax for inputting nodes input_nodes.add(new InputNode("p1", {1})); but that doesn't compile with Java.
  A. Yes sorry about that, instead you have to declare a separate variable, you can do this instead: int addresses_p4[] = {4,5}; input_nodes.add(new InputNode("p4", addresses_p4)); If you wish you can also put a complaint about Java's syntax in the comments.
• Q. The pseudocode declares that if a node receives a table with some information about an address for which it already has a row, but that that the new information is determined to be “better” then the new information should be placed in the table, but should it keep the old information?
  A. No, the pseudocode should probably have read “replaced”. To be clear, there should only ever be at most one entry for each address in any one routing information table at any one time.
• Q. Can I re-submit using the submit command?
  A. Yes, at a terminal type man submit for more information on the submit command, but the relevant section states:

  Should you find on reflection that you wish to amend your answers to an exercise, you may resubmit any files or directories you have already submitted. The original submitted file or directory will be overwritten. Note that if you wish to change a file within a submitted directory, you must resubmit the whole directory. When resubmitting, you will be asked to confirm that you wish to overwrite your original submission.

• Q. Can I assume that the order of the input commands will always be all the 'node' commands, followed by all the 'link' commands followed by the 'send' commands?
  A. Yes, this practical is not intended to test your input file parsing abilities so I've tried to make it as simple as possible.
• Q. Can I always assume that the input files will be valid?
  A. Yes, in particular you can assume that any 'send' or 'link' commands will only reference node names which have been previously defined by a 'node' command.
• Q. Can I use multiple source files?
  A. Yes, that's absolutely fine.

Grading

Grading: The final exam counts for 75%, and the coursework (and project at level 11) count for 25%.

Exams

Note that there has been a substantial revision of the module in the academic year 2001/2, and a minor one in 2002/3. Nevertheless you should find some questions on past exam papers useful for revision purposes.

• Past exams

Course Texts

This year there is no required text book. The course however largely follows portions of the textbook: George Coulouris, Jean Dollimore and Tim Kindberg, Distributed Systems: Concepts and Design 5th Edition There is also a largely relevant 4th Edition which you may find cheaper.

Our part two "Fundamentals" will comprise a brief look at several chapters: Fundamental Models, Networking, Interprocess Communication. The remaining parts will stick mostly with the chapters of the book: Time and Global State, Coordination and Agreement, Operating System Support, Peer-to-Peer and Security. Those as with any course there will be parts on the course not in the book and vice-versa.

Other related texts

Include:

• Andrew S. Tanenbaum and Maarten Van Steen, Distributed Systems: Principles and Paradigms, Prentice Hall, September 2001 web site
• Nancy A. Lynch, Distributed Algorithms, Morgan Kaufmann, 1996
• Andrew S. Tanenbaum, Computer Networks, 3rd ed., Prentice- Hall, 1996.
• R. Chow and T. Johnson, Distributed Operating systems and Algorithms, Addison-Wesley, 1997.

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These pages will be updated regularly as the course progresses in particular with a copy of the lecture slides.