1.1. (5 pts) Visit the class discussion group (link available in the syllabus page). Post a message with your full name as the subject line. In your post, briefly introduce yourself (including your full name) and one item you most desire to learn in this class. Throughout this class, you shall regularly participate at the discussion group to find recent announcements, reminders, and discussions.

1.2. Answer the following questions. Cite your source(s).

Note: Not all information published on the web are correct; discern the validity of the information you use.

1) (5 pts) What is ubiquitous computing? What is the relationship between ubiquitous computing and mobile computing?

2) (5 pts) What is the relationship between pervasive computing and wireless computing?

3) (5 pts) Some believe that the Internet itself is a distributed system. Do you agree with this statement? Justify your answer.

4) (5 pts) What is the relationship between reliability and security of a system?

5) (5 pts) Explain what reliability means. Is reliability related to failure processing? Justify your answer.

6) (5 pts) Explain what scalability means in a distributed system. Give an example of a system or an algorithm that has poor scalability.

7) (10 pts) What is a middleware? What is the role played by middleware in a distributed system?

1.3. Suppose John is using his laptop to send a piece of data (d) to Mary. Below are some assumptions.

Assumptions:

(a) The IP of John’s laptop is John_IP, and its MAC/physical address is John_MAC.

(b) Mary’s computer’s IP address is Mary_IP, and its MAC is Mary_MAC.

(c) The IP of the default gateway/router of John’s laptop is John_Router_IP, and its MAC is John_Router_MAC.

Answer the following questions:

8) (5 pts) How would the Layer-3 header (i.e., IP header) be structured? Hint: Show the source address and the destination address.

9) (5 pts) How would the Layer-2 header be structured? Hint: Show the source address and the destination address.

10) (5 pts) Explain how John’s default router would process the packet sent from John’s computer.

1.4. Encapsulation vs Tunneling:

11) (10 pts) What does encapsulation means in networking protocols? Give two examples of tunneling protocols.

12) (10 pts) What does tunneling means in networking protocols? Give two examples of tunneling protocols.

1.5. Inter-process communication: Suppose process A has sent a message to process B.

13) (10 pts) When the communication is synchronous, what does that mean? Give an example of synchronous communication.

14) (10 pts) When the communication is asynchronous, what does that mean? Give an example of asynchronous communication.

Go to the Index

Lab 2

Total: 100 points

2.1 (10 pts) In Figure 4.6, the TCP server program uses two different sockets. One is the ServerSocket class and the other is the Socket class. Explain how those two different kinds of sockets are used by the TCP server program.

2.2 (10 pts) The sockets abstraction may be implemented as a UDP socket or a TCP socket. Explain the relative pros and cons of UDP sockets and TCP sockets.

2.3 (10 pts) In Chapter 5 (Remote Invocation), it is said that RPC provides at least two types of transparency: the location transparency and the access transparency. First, explain what each of those two means; secondly, explain whether one is implied by the other. Justify your answer.

2.4 (20 pts) Suppose you’d like to add location transparency to the Request-Reply model as discussed in Chapter 5; that is, a client does not need to specify the server’s specific location in order to send a request to that server. Explain your design. Feel free to use a diagram to illustrate your design. Provide sufficient detail about how the client and the servers would communicate.

2.5 (10 pts) If a communication paradigm is asynchronous, is it also time-uncoupled? Explain your answer with examples as appropriate.

2.6 (10 pts) If a communication paradigm is synchronous, is it also time-coupled? Explain your answer with examples as appropriate.

2.7 (30 pts) Perform a comparative study of message passing and distributed shared memory (in chapter 6). Would one of them be more efficient than the other? First, analyze the pros and cons of each approach; then consider different application scenarios when answering the given question.

Go to the Index

Development project

NOTES:

(a) This can be an individual project or a two-person team project. Clearly indicate your team status when submitting your project (on the top page of the documentation).

(b) Each person must submit the project, even if you are in a two-person team.

- Objectives: This project provides hands-on experience of developing distributed systems, in particular a system based on the service brokerage pattern discussed in class. More discussions about brokers can be found in the textbook, in particular Chapter 2 (System Architectures) and Chapter 6 (Indirect Communication).

Figure 1. The Brokerage pattern

- Description: As shown in Figure 1, there exist three types of entities in the system.

a) A service provider provides services, which may be requested by clients (that is, requesters).

b) A service requester may request a service from a service provider.

c) The service broker is in charge of keeping an inventory of services published by service providers and, when requested by a service requester, provides related service information in response to the request.

This project has two parts.

In part A, each team should develop the following programs.

1) The service broker:

§ The broker uses a well-known port, which is to be used by both the service providers and the service requesters when communicating with the service broker.

§ The broker should support the service providers by allowing them to send addService( ) and removeService( ) requests to the broker. The addService( ) request from a service provider causes the broker to add the name of the service, the IP address of the provider, and the port number to be used for that service. The removeService( ) request causes the broker to find and remove the named service from its directory of services.

§ The broker should support the service requesters by allowing them to send discoverService( ) requests, which include a key phrase of the requested service. The broker should look up services in the service directory using the specified key phrase, and return the service provider that best matches that key phrase; if no matching service is found, it returns an error code to the requester.

2) Service provider #1: The randomNumberGenerator provider supplies a random number to the requester.

3) Service provider #2: The hashGenerator provider takes a string (for example, “How are you doing?”) and the name of a hash method (for example, MD5) as the input from the client and returns the hash value generated from the given string using the specified hash method. The string “How are you doing?”, for instance, will be hashed into the hash value “60F4A68C292CF0E697C9E65057DCB5B4” (in hexadecimal). Use the online hash calculator at https://www.pelock.com/products/hash-calculator to verify the hash value produced by your hashGenerator provider.

Both providers must request the service broker to add their services to the directory, via the addService( ) request. They may remove their respected services from the directory by sending the removeService( ) request to the broker.

4) The client (i.e., service requester) should provide an appropriate user interface allowing the user to specify or choose what the user would want the client program to do; this user input process should continue until the user chooses to exit from the program.

a. If the user chooses to get a hash value for a given string using the chosen hashing method, the service requester will first send a discoverService( ) request to the broker in order to find the IP and port# of the service provider; it then sends a message to the provider (with the source string and the hash method as the input parameters) and, in return, gets the hash value back from the provider. Once the hash value is available, the requester then displays it on the user screen.

b. If the user chooses to get a random number, the service requester will first send a discoverService( ) request to the broker in order to find the IP and port# of the service provider; it then sends a message to the provider and, in return, gets a random number back from the provider. Once the random number is available, the requester then displays it on the user screen.

c. If the user’s request cannot be handled, the requester should print appropriate error messages on the user screen.

In part B of the project, each team should revise the programs from part A by adding the following enhancements.

1) The service broker will authenticate the provider first before adding the requested service to the directory. For example, the broker may require a provider to register itself first with the broker, with an id and password. If password-based authentication is used to authenticate the provider, the addService( ) and the removeService( ) requests may need to include the provider’s id and password as part of the parameters.

2) (Bonus, 20% more) In addition to the password-based authentication, you may implement two-factor authentication. That is, in addition to the id and password, the broker may send a one-time code to the requesting provider and require the provider to include that one-time code when requesting to add a service or remove a service.

- To hand in:

a) Part A specification:

Clearly specify the communication protocols between the entities, including those between the broker and the provider, between the broker and the requester, and between the requester and the provider.

b) Part A complete programs:

Include the design documents and the complete source programs in a single zip file, and submit the zip file in Blackboard.

Give the TA a demo of your running program. The demo should be completed within a week after the due date.

c) Part B complete programs:

Include the design documents and the complete source programs in a single zip file, and submit the zip file in Blackboard.

Give the TA a demo of your running program. The demo should be completed within a week after the due date.

Go to the Index