Computer Science, Paper II

An instruction requires five stages to execute:

(a) Answer the Following Questions:

(i) Is it possible for an organization’s Web server and mail server to have exactly the same alias for a hostname (for example, foo.com)? What would be the type for the RR that contains the hostname of the mail server?

(ii) Draw the structure of Internet in terms of ISPs, also show the concept in terms of Edge and Core networks.

(iii) A packet switch receives a packet to be forwarded. When the packet arrives, one other packet is halfway done being transmitted on this outbound link and four other packets are waiting to be transmitted in FIFO manner. Suppose all packets are 1,500 bytes and the link rate is 2 Mbps. What is the queuing delay for the packet?

(iv) Why do HTTP, FTP, SMTP, and POP3 run on top of TCP rather than on UDP?

(b) (i) Why do we need conditional GET when we have regular GET with respect to HTTP? What is its difference in comparison to GET?

(ii) With respect to web caching, if an average object size is 100K bits and the average request rate from browsers to origin servers is 15/sec. Suppose RTT from an institutional router to any origin server is 2 sec. If LAN speed is 100Mbps and access link speed is 1.54 Mbps then with a cache hit of 50%, how much total delay will be there?

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(a) Consider the following pseudo code for producer and consumer:

// producerdo{

//produce an item

//place in buffer

}while(true);

// consumerdo{

// remove item from buffer

// consumes item

}while(true);

(i) What is race condition?

(ii) Is there any possibility of the race condition if two threads named producer and consumer simultaneously execute the above functions? Provide the reasoning in two-three sentences.

(iii) Add the necessary synchronization in the above functions, you may use semaphores or mutex. You may provide just pseudo code or exact C/C++ code.

(iv) Consider a process that uses a user level threading library to spawn 10 user level threads. The library maps these 10 threads on to 2 kernel threads. The process is executing on a 8-core system. What is the maximum number of threads of a process that can be executing in parallel?

(b) Consider a multi-level memory management scheme with the following format for virtual addresses:

Virtual Page # (10 bits) | Virtual Page # (10 bits) | Offset (12 bits)

Virtual addresses are translated into physical addresses of the following form:

Physical Page # (20 bits) | Offset (12 bits)

Page table entries (PTE) are 32 bits and contain the 20-bit physical page number and OS bookkeeping bits (e.g., valid, dirty, used, etc.).

(i) How big is a page?

(ii) What is the maximum amount of memory (in bytes) in a single virtual address space? Explain your answer.

(iii) What is the maximum amount of physical memory (in bytes) that this memory management scheme supports? Explain your answer.

(iv) Sketch the format of the page table for the multi-level virtual memory management scheme. Illustrate the process of resolving an address as well as possible. Assume there is no TLB or cache.

(a) Answer the questions i, ii, according to given schema.

[Schema diagram: REGIONS, DEPARTMENTS, EMPLOYEES, COUNTRIES, JOBS, LOCATIONS, JOB_HISTORY tables with their fields and relationships]

(i) Display the length of first name and length of second name for employees where last name contains character ‘b’ after 3rd position.

(ii) Display job title, department name, employee last name, starting date for all jobs from 1992 to 1998.

(iii) Differentiate between Left outer join, Right outer join and Full outer join. Explain your answer with the help of Venn Diagram.

(b) Provide brief answers to the following questions:

(i) Differentiate between Single row Sub-Query and Multi row Sub-Query and write a sample query too.

(ii) Discuss the role of Primary Keys, foreign keys, and indexes in database schema. Also, explain their significance in ensuring data accuracy, enforcing referential integrity and improving query performance.