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Reliable protocols depend on error detection algorithms to detect transmission errors. The following questions will reinforce your understanding of these algorithms.
Reliable protocols rely on different types of checksums to verify whether frames have been affected by transmission errors. The most frequently used checksums are :
the Internet checksum used by UDP, TCP and other Internet protocols which is defined in :rfc:`1071` and implemented in various libraries.
the 16 bits or the 32 bits Cyclical Redundancy Checks (CRC) that are often used on disks, in zip archives and in datalink layer protocols. See for CRC-32 implementations in various languages.
The Cyclic Redundancy Checks (CRCs) are efficient error detection codes that are able to detect :
all errors that affect an odd number of bits
all errors that affect a sequence of bits which is shorter than the length of the CRC
Implement a small software that computes the CRC-32 for a text file. Then, modify the contents of the file to change an even number of bits or an odd number of bits inside the file. When modifying the file, remember that an ASCII file is composed of 8 bits characters that are encoded by using the ASCII table that you can find at : . You can also write a small program that produces binary files that are a small variation of each other.
Discussion questions
Consider two high-end servers connected back-to-back by using a 10 Gbps interface. If the delay between the two servers is one millisecond, what is the throughput that can be achieved by a reliable protocol that is using 10,000 bits frames and a window of
one frame
ten frames
hundred frames
Is it possible for a go-back-n receiver to inter-operate with a selective-repeat sender ? Justify your answer.
Is it possible for a selective-repeat receiver to inter-operate with a go-back-n sender ? Justify your answer.
Same question as above, but assume now that both the sender and the receiver implement selective repeat. Note that the answer can be different from the above question.


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locale/cs/LC_MESSAGES/exercises/reliability.po, string 38