Question from OS 1.UDP is transfer protocol used in internet applications which

Question

Question from OS

1.UDP is transfer protocol used in internet applications which does not guarantee that all packets are delivered, that packets will be delivered in order that they or sent, nor that packets may not arrive more than once. Explain why any application would use such a protocol as opposed to TCP which does guarantee all of these things.

2.. In a system that uses paging, a process cannot access memory that belongs to another process. Why? Why is it theoretically possible with segmentation but not paging?

Explanation / Answer

1. TCP and UDP
Though TCP is reliable protocol and have many advantages, there are stituations where UDP is used:
a. In situations where you really want to get a simple answer to another server quickly, UDP works at its best. Generally, you want the answer to be in one response packet, and yet are prepared to implement your own protocol for reliability or to resend.

b. Another case is when one is delivering data that can be lost because newer data coming in will replace the previous data/state. Whether data,video streaming, a stock quotation service(Not used for actual treading), or gaming data comes to mind.

c. Another case is when you are managing a tremendous amount of state and you want to avoid using TCP because the OS cannot handle that many sessions. Though this is rare case today.

d. The point here is the overhead in negotiating for TCP socket and handshaking the TCP packets is huge. There is no appreciable UDP overhead.

e. Also, one other is for multicast traffic. UDP can be multicasted to multiple hosts where as TCP cannot do this at all.

2. In any system that uses paging:

i. An address on a paging system is a logical page number and an offset. The physical page is found by searching a table based on the logical page number to produce a physical page number.

ii As the operating system controls the contents of this table, it can limit a process to accessing only those physical pages allocated to the process.

iii. There is no way for a process to refer to a page it does not own because the page will not be in the page table.

iv. To allow such access, an operating system simply needs to allow entries for non-process memory to be added to the process' page table.

v. This is useful when two or more processes need to exchange data they just read and write to the same physical addresses (which may be at varying logical addresses)

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