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# Copyright (C) 2019 Olivier Bonaventure
# This file is distributed under the same license as the Computer networking
# : Principles, Protocols and Practice package.
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msgstr ""
"Project-Id-Version: Computer networking : Principles, Protocols and "
"Practice 3\n"
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#: ../../exercises/ex-sharing.rst:6
msgid ""
"This is an unpolished draft of the third edition of this e-book. If you "
"find any error or have suggestions to improve the text, please create an "
"issue via https://github.com/CNP3/ebook/issues?milestone=3 or help us by "
"providing pull requests to close the existing issues."
msgstr ""

#: ../../exercises/ex-sharing.rst:11
msgid "Sharing resources"
msgstr ""

#: ../../exercises/ex-sharing.rst:15
msgid "Medium Access Control"
msgstr ""

#: ../../exercises/ex-sharing.rst:17
msgid ""
"To understand the operation of Medium Access Control algorithms, it is "
"often interesting to use a geometric representation of the transmission "
"of frames on a shared medium. This representation is suitable if the "
"communicating devices are attached to a single cable. Consider a simple "
"scenario with a host connected at one end of a cable. For simplicity, let"
" us consider a cable that has a length of one kilometer. Let us also "
"consider that the propagation delay of the electrical signal is five "
"microseconds per kilometer. The figure below shows the transmission of a "
"2000 bits frame at 100 Mbps by host A on the cable."
msgstr ""

#: ../../exercises/ex-sharing.rst:42
msgid ""
"If the transmitting host is located at another position on the shared "
"medium than one of the edges, then the geometrical pattern that "
"represents the transmission of a frame is slightly different. If the "
"transmitting host is placed in the middle of the cable, then the signal "
"is transmitted in both directions on the cable. The figure below shows "
"the transmission of one 100 bits frame at 100 Mbps by host C on the same "
"cable."
msgstr ""

#: ../../exercises/ex-sharing.rst:66
msgid ""
"In a shared medium, a collision may happen if two hosts transmit at "
"almost the same time as shown in the example below."
msgstr ""

#: ../../exercises/ex-sharing.rst:92
msgid ""
"Consider the following scenario for the ALOHA medium access control "
"algorithm. Three hosts are attached to a one-kilometer long cable and "
"transmit 1000 bits frames at 1 Mbps. Each arrow represents a request to "
"transmit a frame on the corresponding host. Each square represents 250 "
"microseconds in the figure. Represent all the transmitted frames and list"
" the frames that collide."
msgstr ""

#: ../../exercises/ex-sharing.rst:119
msgid ""
"Same question as above, but now consider that the hosts transmit 1000 "
"bits frames at 100 Mbps. The cable has a length of 2 kilometers. C is in "
"the middle of the cable. Each square in the figure below corresponds to "
"10 microseconds."
msgstr ""

#: ../../exercises/ex-sharing.rst:150
msgid ""
"In ALOHA, the hosts rely on acknowledgments to detect whether their frame"
" has been received correctly by the destination. Consider a network "
"running at 100 Mbps where the host exchange 1000 bits frames and "
"acknowledgments of 100 bits. Draw the frames sent by hosts A and B in the"
" figure below. Assume that a square corresponds to 10 microseconds and "
"that the cable has a length of 2 kilometers."
msgstr ""

#: ../../exercises/ex-sharing.rst:175
msgid ""
"Same question as above, but now assume that the retransmission timer of "
"each host is set to 50 microseconds."
msgstr ""

#: ../../exercises/ex-sharing.rst:203
msgid ""
"In practice, hosts transmit variable length frames. Consider a cable "
"having a bandwidth of 100 Mbps and a length of 2 kilometers."
msgstr ""

#: ../../exercises/ex-sharing.rst:231
msgid ""
"With CSMA, hosts need to listen to the communication channel before "
"starting their transmission. Consider again a 2 kilometers long cable "
"where hosts send frames at 100 Mbps. Show in the figure below the correct"
" transmission of frames with CSMA."
msgstr ""

#: ../../exercises/ex-sharing.rst:260
msgid ""
"CSMA/CD does not use acknowledgments but instead assumes that each host "
"can detect collisions by listening while transmitting. Consider a 2 "
"kilometers long cable running at 10 Mbps. Show in the figure below the "
"utilization of the communication channel and the collisions that would "
"occur. For this exercise, do not attempt to retransmit the frames that "
"have collided."
msgstr ""

#: ../../exercises/ex-sharing.rst:290
msgid ""
"Consider again a network that uses CSMA/CD. This time, the bandwidth is "
"set to 1 Gbps and the cable has a length of two kilometers. When a "
"collision occurs, consider that the hosts B and C retransmit immediately "
"while host A waits for the next slot."
msgstr ""

#: ../../exercises/ex-sharing.rst:316
msgid ""
"An important part of the CSMA/CD algorithm is the exponential backoff. To"
" illustrate the operation of this algorithm, let us consider a cable that"
" has a length of one kilometer. The bandwidth of the network is set to 10"
" Mbps. Assume that when a collision occurs, host A always selects the "
"highest possible random delay according to the exponential backoff "
"algorithm while host B always selects the shortest one. In this network, "
"the slot time is equal to the time required to transmit 100 bits. We "
"further assume that a host can detect collision immediately (i.e. as soon"
" as the other frame arrives)."
msgstr ""

#: ../../exercises/ex-sharing.rst:343
msgid "Fairness and congestion control"
msgstr ""

#: ../../exercises/ex-sharing.rst:345
msgid ""
"Consider the network below. Compute the max-min fair allocation for the "
"hosts in this network assuming that nodes `Sx` always send traffic "
"towards node `Dx`. Furthermore, link `R1-R2` has a bandwidth of 10 Mbps "
"while link `R2-R3` has a bandwidth of 20 Mbps."
msgstr ""

#: ../../exercises/ex-sharing.rst:382
msgid ""
"To understand congestion control algorithms, it can also be useful to "
"represent the exchange of packets by using a graphical representation. As"
" a first example, let us consider a very simple network composed of two "
"hosts interconnected through a switch."
msgstr ""

#: ../../exercises/ex-sharing.rst:399
msgid ""
"Suppose now that host A uses a window of three segments and sends these "
"three segments immediately. The segments will be queued in the router "
"before being transmitted on the output link and delivered to their "
"destination. The destination will reply with a short acknowledgment "
"segment. A possible visualization of this exchange of packets is "
"represented in the figure below. We assume for this figure that the "
"router marks the packets to indicate congestion as soon as its buffer is "
"non-empty when its receives a packet on its input link. In the figure, a "
"`(c)` sign is added to each packet to indicate that it has been "
"explicitly marked."
msgstr ""

#: ../../exercises/ex-sharing.rst:432
msgid ""
"In practice, a router is connected to multiple input links. The figure "
"below shows an example with two hosts."
msgstr ""

#: ../../exercises/ex-sharing.rst:491
msgid ""
"In general, the links have a non-zero delay. This is illustrated in the "
"figure below where a delay has been added on the link between `R` and "
"`C`."
msgstr ""

#: ../../exercises/ex-sharing.rst:538 ../../exercises/ex-sharing.rst:613
msgid "Consider the network depicted in the figure below."
msgstr ""

#: ../../exercises/ex-sharing.rst:558
msgid ""
"In this network, compute the minimum round-trip-time between `A` (resp. "
"`B`) and `D`. Perform the computation if the hosts send segments "
"containing 1000 bits."
msgstr ""

#: ../../exercises/ex-sharing.rst:559
msgid ""
"How is the maximum round-trip-time influenced if the buffers of router "
"`R1` store 10 packets ?"
msgstr ""

#: ../../exercises/ex-sharing.rst:560
msgid ""
"If hosts `A` and `B` send to `D` 1000 bits segments and use a sending "
"window of four segments, what is the maximum throughput that they can "
"achieve ?"
msgstr ""

#: ../../exercises/ex-sharing.rst:561
msgid ""
"Assume now that `R1` is using round-robin scheduling instead of a FIFO "
"buffer. One queue is used to store the packets sent by `A` and another "
"for the packets sent by `B`. `A` sends one 1000 bits packet every second "
"while `B` sends packets at 10 Mbps. What is the round-trip-time measured "
"by each of these two hosts if each of the two queues of `R1` can store 5 "
"packets ?"
msgstr ""

#: ../../exercises/ex-sharing.rst:564
msgid ""
"When analyzing the reaction of a network using round-robin schedulers, it"
" is sometimes useful to consider that the packets sent by each source are"
" equivalent to a fluid and that each scheduler acts as a tap. Using this "
"analogy, consider the network below. In this network, all the links are "
"100 Mbps and host `B` is sending packets at 100 Mbps. If A sends at 1, 5,"
" 10, 20, 30, 40, 50, 60, 80 and 100 Mbps, what is the throughput that "
"destination `D` will receive from `A`. Use this data to plot a graph that"
" shows the portion of the traffic sent by host `A` which is received by "
"host `D`."
msgstr ""

#: ../../exercises/ex-sharing.rst:582
msgid "Compute the max-min fair bandwidth allocation in the network below."
msgstr ""

#: ../../exercises/ex-sharing.rst:588
msgid "Simple network topology"
msgstr ""

#: ../../exercises/ex-sharing.rst:591
msgid "Consider the simple network depicted in the figure below."
msgstr ""

#: ../../exercises/ex-sharing.rst:609
msgid ""
"In this network, a 250 Kbps link is used between the routers. The "
"propagation delays in the network are negligible. Host `A` sends 1000 "
"bits long segments so that it takes one msec to transmit one segment on "
"the `A-R1` link. Neglecting the transmission delays for the "
"acknowledgments, what is the minimum round-trip time measured on host `A`"
" with such segments ?"
msgstr ""

#: ../../exercises/ex-sharing.rst:610
msgid ""
"If host `A` uses a window of two segments and needs to transmit five "
"segments of data. How long does the entire transfer lasts ?"
msgstr ""

#: ../../exercises/ex-sharing.rst:611
msgid ""
"Same question as above, but now host `A` uses the simple DECBIT "
"congestion control mechanism and a maximum window size of four segments."
msgstr ""

#: ../../exercises/ex-sharing.rst:630
msgid ""
"Hosts `A` and `B` use the simple congestion control scheme described in "
"the book and router `R1` uses the DECBIT mechanism to mark packets as "
"soon as its buffers contain one packet. Hosts `A` and `B` need to send "
"five segments and start exactly at the same time. How long does each "
"hosts needs to wait to receive the acknowledgment for its fifth segment ?"
msgstr ""

#: ../../exercises/ex-sharing.rst:633
msgid "Discussion questions"
msgstr ""

#: ../../exercises/ex-sharing.rst:639
msgid ""
"In a deployed CSMA/CD network, would it be possible to increase or "
"decrease the duration of the slotTime ? Justify your answer"
msgstr ""

#: ../../exercises/ex-sharing.rst:641
msgid ""
"Consider a CSMA/CD network that contains hosts that generate frames at a "
"regular rate. When the transmission rate increases, the amount of "
"collisions increases. For a given network load, measured in bits/sec, "
"would the number of collisions be smaller, equal or larger with short "
"frames than with long frames ?"
msgstr ""

#: ../../exercises/ex-sharing.rst:643
msgid ""
"Slotted ALOHA improves the performance of ALOHA by dividing the time in "
"slots. However, this basic idea raises two interested questions. First "
"how would you enforce the duration of these slots ? Second, should a slot"
" include the time to transmit a data frame or the time to transmit a data"
" frame and the corresponding acknowledgment ?"
msgstr ""

#: ../../exercises/ex-sharing.rst:645
msgid ""
"Like ALOHA, CSMA relies on acknowledgments to detect where a frame has "
"been correctly received. When a host senses an idle channel, if should "
"transmit its frame immediately. How should it react if it detects that "
"another host is already transmitting ? Consider two options :"
msgstr ""

#: ../../exercises/ex-sharing.rst:647
msgid ""
"the host continues to listen until the communication channel becomes "
"free. It transmits as soon as the communication channel becomes free."
msgstr ""

#: ../../exercises/ex-sharing.rst:648
msgid ""
"the host stops to listen and waits for a random time before sensing again"
" the communication channel to check whether it is free."
msgstr ""

