msgid "" msgstr "" "Project-Id-Version: Czech (cnp3-ebook)\n" "Report-Msgid-Bugs-To: \n" "POT-Creation-Date: 2026-04-19 12:17+0200\n" "PO-Revision-Date: YEAR-MO-DA HO:MI+ZONE\n" "Last-Translator: FULL NAME \n" "Language-Team: Czech \n" "Language: cs\n" "MIME-Version: 1.0\n" "Content-Type: text/plain; charset=UTF-8\n" "Content-Transfer-Encoding: 8bit\n" "Plural-Forms: nplurals=3; plural=(n==1) ? 0 : (n>=2 && n<=4) ? 1 : 2;\n" "X-Generator: Weblate 5.14.3\n" #: ../../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 ""