Translation

English
English Czech Actions
A version of the Alternating Bit Protocol supporting variable length frames uses a header that contains the following fields :
a `number` (0 or 1)
a `length` field that indicates the length of the data
a Cyclic Redundancy Check (`CRC`)
Derive a mathematical expression that provides the `goodput`, i.e. the amount of payload bytes that have been transmitted during a period of time, achieved by the Alternating Bit Protocol assuming that :
Each frame contains `D` bytes of data and `c` bytes of control information
Each acknowledgment contains `c` bytes of control information
The bandwidth of the two directions of the link is set to `B` bits per second
The delay between the two hosts is `s` seconds in both directions
there are no transmission errors
when there are no losses
when every second acknowledgment is discarded due to transmission errors
Same question when using selective repeat instead of go-back-n. Note that the answer is not necessarily the same.
Practice
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 http://rosettacode.org/wiki/CRC-32 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 : 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.
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

Loading…

User avatar None

New source string

cnp3-ebook / exercises/reliabilityCzech

New source string 4 years ago
Browse all component changes

Glossary

English Czech
No related strings found in the glossary.

String information

Source string location
../../exercises/reliability.rst:44
String age
4 years ago
Source string age
4 years ago
Translation file
locale/cs/LC_MESSAGES/exercises/reliability.po, string 21