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File “locale/pot/exercises/reliability.pot” was added. 3 years ago
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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 ?
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 ?
3 years ago
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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.
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.
3 years ago
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By using your knowledge of the Internet checksum, can you find a transmission error that will not be detected by these checksums?
By using your knowledge of the Internet checksum, can you find a transmission error that will not be detected by these checksums?
3 years ago
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the Fletcher checksum [Fletcher1982]_, see https://en.wikipedia.org/wiki/Fletcher%27s_checksum for implementation details.
the Fletcher checksum [Fletcher1982]_, see https://en.wikipedia.org/wiki/Fletcher%27s_checksum for implementation details.
3 years ago
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when the third and seventh frames are lost
when the third and seventh frames are lost
3 years ago
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Consider a go-back-n sender and a go-back receiver that are directly connected with a 10 Mbps link that has a propagation delay of 100 milliseconds. Assume that the retransmission timer is set to three seconds. If the window has a length of 4 frames, draw a time-sequence diagram showing the transmission consisting of 10 data frames (each frame contains 10000 bits):
Consider a go-back-n sender and a go-back receiver that are directly connected with a 10 Mbps link that has a propagation delay of 100 milliseconds. Assume that the retransmission timer is set to three seconds. If the window has a length of 4 frames, draw a time-sequence diagram showing the transmission consisting of 10 data frames (each frame contains 10000 bits):
3 years ago
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To speedup the transmission of the frames, a student proposes to compute the CRC over the data part of the frame but not over the header. What do you think of this proposed solution ?
To speedup the transmission of the frames, a student proposes to compute the CRC over the data part of the frame but not over the header. What do you think of this proposed solution ?
3 years ago
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Consider a `b` bits per second link between two hosts that has a propagation delay of `t` seconds. Derive a formula that computes the time elapsed between the transmission of the first bit of a `d` bytes frame from a sending host and the reception of the last bit of this frame on the receiving host.
Consider a `b` bits per second link between two hosts that has a propagation delay of `t` seconds. Derive a formula that computes the time elapsed between the transmission of the first bit of a `d` bytes frame from a sending host and the reception of the last bit of this frame on the receiving host.
3 years ago

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