cnp3-ebook/exercises/reliability

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24 ../../exercises/reliability.rst:49

	English Reliable protocols rely on different types of checksums to verify whether frames have been affected by transmission errors. The most frequently used checksums are : 164/10000 · 164
25 ../../exercises/reliability.rst:51

	English the Internet checksum used by UDP, TCP and other Internet protocols which is defined in :rfc:`1071` and implemented in various libraries. 137/10000 · 137
26 ../../exercises/reliability.rst:52

	English 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 http://rosettacode.org/wiki/CRC-32 for CRC-32 implementations in various languages. 226/10000 · 226
27 ../../exercises/reliability.rst:53

	English the Fletcher checksum [Fletcher1982]_, see https://en.wikipedia.org/wiki/Fletcher%27s_checksum for implementation details. 122/10000 · 122
28 ../../exercises/reliability.rst:55

	English By using your knowledge of the Internet checksum, can you find a transmission error that will not be detected by these checksums? 129/10000 · 129
29 ../../exercises/reliability.rst:57

	English The Cyclic Redundancy Checks (CRCs) are efficient error detection codes that are able to detect : 97/10000 · 97
30 ../../exercises/reliability.rst:59

	English all errors that affect an odd number of bits 44/10000 · 44
31 ../../exercises/reliability.rst:60

	English all errors that affect a sequence of bits which is shorter than the length of the CRC 85/10000 · 85
32 ../../exercises/reliability.rst:62

	English 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 : http://en.wikipedia.org/wiki/ASCII . You can also write a small program that produces binary files that are a small variation of each other. 473/10000 · 473
33 ../../exercises/reliability.rst:64

	English Checksums and CRCs should not be confused with secure hash functions such as MD5 defined in :rfc:`1321` or SHA-1 described in :rfc:`4634`. Secure hash functions are used to ensure that files or sometimes frames/packets/segments have not been modified. Secure hash functions aim at detecting malicious changes while checksums and CRCs only detect random transmission errors. Use the `shasum <http://linux.die.net/man/1/shasum>`_ or `md5sum <http://linux.die.net/man/1/md5sum>`_ programs on Linux to perform the same tests as above. 530/10000 · 530
34 ../../exercises/reliability.rst:68

	English Discussion questions 20/10000 · 20
35 ../../exercises/reliability.rst:70

	English 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 255/10000 · 255
36 ../../exercises/reliability.rst:72

	English one frame 9/10000 · 9
37 ../../exercises/reliability.rst:73

	English ten frames 10/10000 · 10
38 ../../exercises/reliability.rst:74

	English hundred frames 14/10000 · 14
39 ../../exercises/reliability.rst:76

	English Is it possible for a go-back-n receiver to inter-operate with a selective-repeat sender ? Justify your answer. 110/10000 · 110
40 ../../exercises/reliability.rst:78

	English Is it possible for a selective-repeat receiver to inter-operate with a go-back-n sender ? Justify your answer. 110/10000 · 110
41 ../../exercises/reliability.rst:82

	English A go-back-n sender has sent :math:`2^n` data frames. All the frames have been received correctly and in-order by the receiver, but all the returned acknowledgments have been lost. Show by using a time sequence diagram (e.g. by considering a window of four frames) what happens in this case. Can you fix the problem on the go-back-n sender ? 340/10000 · 340
42 ../../exercises/reliability.rst:84

	English 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. 167/10000 · 167
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