<?xml version="1.0" encoding="UTF-8"?>
<xliff xmlns="urn:oasis:names:tc:xliff:document:1.1" version="1.1">
  <file original="NoName" source-language="en" datatype="plaintext" target-language="en">
    <body>
      <trans-unit xml:space="preserve" approved="no" id="4b16ebd086b232a1" weblate-flags="read-only">
        <source>A closer look at TCP</source>
        <target state="translated">A closer look at TCP</target>
        <context-group name="" purpose="location">
          <context context-type="sourcefile">../../exercises/tcp-2.rst</context>
          <context context-type="linenumber">8</context>
        </context-group>
      </trans-unit>
      <trans-unit xml:space="preserve" approved="no" id="ad47b7c211e17222" weblate-flags="read-only">
        <source>In this series of exercises, you will explore in more details the operation of TCP and its congestion control scheme. TCP is a very important protocol in today's Internet since most applications use it to exchange data. We first look at TCP in more details by injecting segments in the Linux TCP stack and analyze how the stack reacts. Then we study the TCP congestion control scheme.</source>
        <target state="translated">In this series of exercises, you will explore in more details the operation of TCP and its congestion control scheme. TCP is a very important protocol in today's Internet since most applications use it to exchange data. We first look at TCP in more details by injecting segments in the Linux TCP stack and analyze how the stack reacts. Then we study the TCP congestion control scheme.</target>
        <context-group name="" purpose="location">
          <context context-type="sourcefile">../../exercises/tcp-2.rst</context>
          <context context-type="linenumber">10</context>
        </context-group>
      </trans-unit>
      <trans-unit xml:space="preserve" approved="no" id="f119d94b32e69f32" weblate-flags="read-only">
        <source>Injecting segments in the Linux TCP stack</source>
        <target state="translated">Injecting segments in the Linux TCP stack</target>
        <context-group name="" purpose="location">
          <context context-type="sourcefile">../../exercises/tcp-2.rst</context>
          <context context-type="linenumber">14</context>
        </context-group>
      </trans-unit>
      <trans-unit xml:space="preserve" approved="no" id="806ebb8acc5ea844" weblate-flags="read-only">
        <source>Packet capture tools like tcpdump_ and Wireshark_ are very useful to observe the segments that transport protocols exchange. TCP is a complex protocol that has evolved a lot since its first specification :rfc:`793`. TCP includes a large number of heuristics that influence the reaction of a TCP implementation to various types of events. A TCP implementation interacts with the application through the ``socket`` API.</source>
        <target state="translated">Packet capture tools like tcpdump_ and Wireshark_ are very useful to observe the segments that transport protocols exchange. TCP is a complex protocol that has evolved a lot since its first specification :rfc:`793`. TCP includes a large number of heuristics that influence the reaction of a TCP implementation to various types of events. A TCP implementation interacts with the application through the ``socket`` API.</target>
        <context-group name="" purpose="location">
          <context context-type="sourcefile">../../exercises/tcp-2.rst</context>
          <context context-type="linenumber">16</context>
        </context-group>
      </trans-unit>
      <trans-unit xml:space="preserve" approved="no" id="a9954719e4ed2d45" weblate-flags="read-only">
        <source>packetdrill_ is a TCP test suite that was designed to develop unit tests to verify the correct operation of a TCP implementation. A more detailed description of packetdrill_ may be found in [CCB+2013]_. packetdrill_ uses a syntax which is a mix between the C language and the tcpdump_ syntax. To understand the operation of packetdrill_, we first discuss several examples. The TCP implementation in the Linux kernel supports all the recent TCP extensions to improve its performance. For pedagogical reasons, we disable [#fsysctl]_ most of these extensions to use a simple TCP stack. packetdrill_ can be easily installed on recent Linux kernels [#finstall]_.</source>
        <target state="translated">packetdrill_ is a TCP test suite that was designed to develop unit tests to verify the correct operation of a TCP implementation. A more detailed description of packetdrill_ may be found in [CCB+2013]_. packetdrill_ uses a syntax which is a mix between the C language and the tcpdump_ syntax. To understand the operation of packetdrill_, we first discuss several examples. The TCP implementation in the Linux kernel supports all the recent TCP extensions to improve its performance. For pedagogical reasons, we disable [#fsysctl]_ most of these extensions to use a simple TCP stack. packetdrill_ can be easily installed on recent Linux kernels [#finstall]_.</target>
        <context-group name="" purpose="location">
          <context context-type="sourcefile">../../exercises/tcp-2.rst</context>
          <context context-type="linenumber">18</context>
        </context-group>
      </trans-unit>
      <trans-unit xml:space="preserve" approved="no" id="fcfa2b44851729d0" weblate-flags="read-only">
        <source>Let us start with a very simple example that uses packetdrill_ to open a TCP connection on a server running on the Linux kernel. A packetdrill_ script is a sequence of lines that are executed one after the other. There are three main types of lines in a packetdrill_ script.</source>
        <target state="translated">Let us start with a very simple example that uses packetdrill_ to open a TCP connection on a server running on the Linux kernel. A packetdrill_ script is a sequence of lines that are executed one after the other. There are three main types of lines in a packetdrill_ script.</target>
        <context-group name="" purpose="location">
          <context context-type="sourcefile">../../exercises/tcp-2.rst</context>
          <context context-type="linenumber">20</context>
        </context-group>
      </trans-unit>
      <trans-unit xml:space="preserve" approved="no" id="ff933d1ed991798e" weblate-flags="read-only">
        <source>packetdrill_ executes a system call and verifies its return value</source>
        <target state="translated">packetdrill_ executes a system call and verifies its return value</target>
        <context-group name="" purpose="location">
          <context context-type="sourcefile">../../exercises/tcp-2.rst</context>
          <context context-type="linenumber">22</context>
        </context-group>
      </trans-unit>
      <trans-unit xml:space="preserve" approved="no" id="abf628714109a238" weblate-flags="read-only">
        <source>packetdrill_ injects [#ftcpdump_pdrill]_ a packet in the instrumented Linux kernel as if it were received from the network</source>
        <target state="translated">packetdrill_ injects [#ftcpdump_pdrill]_ a packet in the instrumented Linux kernel as if it were received from the network</target>
        <context-group name="" purpose="location">
          <context context-type="sourcefile">../../exercises/tcp-2.rst</context>
          <context context-type="linenumber">23</context>
        </context-group>
      </trans-unit>
      <trans-unit xml:space="preserve" approved="no" id="a33db557f90952b6" weblate-flags="read-only">
        <source>packetdrill_ compares a packet transmitted by the instrumented Linux kernel with the packet that the script expects</source>
        <target state="translated">packetdrill_ compares a packet transmitted by the instrumented Linux kernel with the packet that the script expects</target>
        <context-group name="" purpose="location">
          <context context-type="sourcefile">../../exercises/tcp-2.rst</context>
          <context context-type="linenumber">24</context>
        </context-group>
      </trans-unit>
      <trans-unit xml:space="preserve" approved="no" id="c61e1ece77064146" weblate-flags="read-only">
        <source>For our first packetdrill_ script, we aim at reproducing the simple connection shown in the figure below.</source>
        <target state="translated">For our first packetdrill_ script, we aim at reproducing the simple connection shown in the figure below.</target>
        <context-group name="" purpose="location">
          <context context-type="sourcefile">../../exercises/tcp-2.rst</context>
          <context context-type="linenumber">26</context>
        </context-group>
      </trans-unit>
      <trans-unit xml:space="preserve" approved="no" id="ff7fb30774f1536f" weblate-flags="read-only">
        <source>Let us start with the execution of a system call. A simple example is shown below.</source>
        <target state="translated">Let us start with the execution of a system call. A simple example is shown below.</target>
        <context-group name="" purpose="location">
          <context context-type="sourcefile">../../exercises/tcp-2.rst</context>
          <context context-type="linenumber">57</context>
        </context-group>
      </trans-unit>
      <trans-unit xml:space="preserve" approved="no" id="6bb509a79bab9d0a" weblate-flags="read-only">
        <source>The ``0``  indicates that the system call must be issued immediately. packetdrill_ then executes the system call and verifies that it returns ``3```. If yes, the processing continues. Otherwise the script stops and indicates an error.</source>
        <target state="translated">The ``0``  indicates that the system call must be issued immediately. packetdrill_ then executes the system call and verifies that it returns ``3```. If yes, the processing continues. Otherwise the script stops and indicates an error.</target>
        <context-group name="" purpose="location">
          <context context-type="sourcefile">../../exercises/tcp-2.rst</context>
          <context context-type="linenumber">63</context>
        </context-group>
      </trans-unit>
      <trans-unit xml:space="preserve" approved="no" id="42670939d6dbb7e3" weblate-flags="read-only">
        <source>For this first example, we program packetdrill_ to inject the segments that a client would send. The first step is thus to prepare a :manpage:`socket` that can be used to accept this connection. This socket can be created by using the four system calls below.</source>
        <target state="translated">For this first example, we program packetdrill_ to inject the segments that a client would send. The first step is thus to prepare a :manpage:`socket` that can be used to accept this connection. This socket can be created by using the four system calls below.</target>
        <context-group name="" purpose="location">
          <context context-type="sourcefile">../../exercises/tcp-2.rst</context>
          <context context-type="linenumber">65</context>
        </context-group>
      </trans-unit>
      <trans-unit xml:space="preserve" approved="no" id="89bfed7b30d4b824" weblate-flags="read-only">
        <source>At this point, the socket is ready to accept incoming TCP connections. packetdrill_ needs to inject a TCP segment in the instrumented Linux stack. This can be done with the line below.</source>
        <target state="translated">At this point, the socket is ready to accept incoming TCP connections. packetdrill_ needs to inject a TCP segment in the instrumented Linux stack. This can be done with the line below.</target>
        <context-group name="" purpose="location">
          <context context-type="sourcefile">../../exercises/tcp-2.rst</context>
          <context context-type="linenumber">80</context>
        </context-group>
      </trans-unit>
      <trans-unit xml:space="preserve" approved="no" id="34159386c5db75cf" weblate-flags="read-only">
        <source>Each line of a packetdrill_ script starts with a `timing` parameter that indicates at what time the event specified on this line should happen. packetdrill_ supports absolute and relative timings. An absolute timing is simply a number that indicates the delay in seconds between the start of the script and the event. A relative timing is indicated by using ``+``  followed by a number. This number is then the delay in seconds between the previous event and the current line. Additional information may be found in [CCB+2013]_.</source>
        <target state="translated">Each line of a packetdrill_ script starts with a `timing` parameter that indicates at what time the event specified on this line should happen. packetdrill_ supports absolute and relative timings. An absolute timing is simply a number that indicates the delay in seconds between the start of the script and the event. A relative timing is indicated by using ``+``  followed by a number. This number is then the delay in seconds between the previous event and the current line. Additional information may be found in [CCB+2013]_.</target>
        <context-group name="" purpose="location">
          <context context-type="sourcefile">../../exercises/tcp-2.rst</context>
          <context context-type="linenumber">86</context>
        </context-group>
      </trans-unit>
      <trans-unit xml:space="preserve" approved="no" id="57d76a0cd5b023ee" weblate-flags="read-only">
        <source>The description of TCP packets in packetdrill_ uses a syntax that is very close to the tcpdump_ one. The ``+0`` timing indicates that the line is executed immediately after the previous event. The ``&lt;`` sign indicates that packetdrill_ injects a TCP segment and the ``S`` character indicates that the ``SYN`` flag must be set. Like tcpdump_, packetdrill_ uses sequence numbers that are relative to initial sequence number. The three numbers that follow are the sequence number of the first byte of the payload of the segment (``0``), the sequence number of the last byte of the payload of the segment (``0`` after the semi-column) and the length of the payload (``0`` between brackets) of the ``SYN`` segment. This segment does not contain a valid acknowledgment but advertises a window of 1000 bytes. All ``SYN`` segments must also include the ``MSS`` option. In this case, we set the MSS to 1000 bytes. The next line of the packetdrill_ script verifies the reply sent by the instrumented Linux kernel.</source>
        <target state="translated">The description of TCP packets in packetdrill_ uses a syntax that is very close to the tcpdump_ one. The ``+0`` timing indicates that the line is executed immediately after the previous event. The ``&lt;`` sign indicates that packetdrill_ injects a TCP segment and the ``S`` character indicates that the ``SYN`` flag must be set. Like tcpdump_, packetdrill_ uses sequence numbers that are relative to initial sequence number. The three numbers that follow are the sequence number of the first byte of the payload of the segment (``0``), the sequence number of the last byte of the payload of the segment (``0`` after the semi-column) and the length of the payload (``0`` between brackets) of the ``SYN`` segment. This segment does not contain a valid acknowledgment but advertises a window of 1000 bytes. All ``SYN`` segments must also include the ``MSS`` option. In this case, we set the MSS to 1000 bytes. The next line of the packetdrill_ script verifies the reply sent by the instrumented Linux kernel.</target>
        <context-group name="" purpose="location">
          <context context-type="sourcefile">../../exercises/tcp-2.rst</context>
          <context context-type="linenumber">88</context>
        </context-group>
      </trans-unit>
      <trans-unit xml:space="preserve" approved="no" id="40de10c17f7ae9f4" weblate-flags="read-only">
        <source>This TCP segment is sent immediately by the stack. The ``SYN`` flag is set and the dot next to the ``S`` character indicates that the ACK flag is also set. The SYN+ACK segment does not contain any data but its acknowledgment number is set to 1 (relative to the initial sequence number). For outgoing packets, packetdrill_ does not verify the value of the advertised window. In this line, it also accepts any TCP options (``&lt;...&gt;``).</source>
        <target state="translated">This TCP segment is sent immediately by the stack. The ``SYN`` flag is set and the dot next to the ``S`` character indicates that the ACK flag is also set. The SYN+ACK segment does not contain any data but its acknowledgment number is set to 1 (relative to the initial sequence number). For outgoing packets, packetdrill_ does not verify the value of the advertised window. In this line, it also accepts any TCP options (``&lt;...&gt;``).</target>
        <context-group name="" purpose="location">
          <context context-type="sourcefile">../../exercises/tcp-2.rst</context>
          <context context-type="linenumber">95</context>
        </context-group>
      </trans-unit>
      <trans-unit xml:space="preserve" approved="no" id="e436fe10a2070a1a" weblate-flags="read-only">
        <source>The third segment of the three-way handshake is sent by packetdrill_ after a delay of 0.1 seconds. The connection is now established and the accept system call will succeed.</source>
        <target state="translated">The third segment of the three-way handshake is sent by packetdrill_ after a delay of 0.1 seconds. The connection is now established and the accept system call will succeed.</target>
        <context-group name="" purpose="location">
          <context context-type="sourcefile">../../exercises/tcp-2.rst</context>
          <context context-type="linenumber">98</context>
        </context-group>
      </trans-unit>
      <trans-unit xml:space="preserve" approved="no" id="f9e38074e996260f" weblate-flags="read-only">
        <source>The :manpage:`accept` system call returns a new file descriptor, in this case value ``4``. At this point, packetdrill_ can write data on the socket or inject packets.</source>
        <target state="translated">The :manpage:`accept` system call returns a new file descriptor, in this case value ``4``. At this point, packetdrill_ can write data on the socket or inject packets.</target>
        <context-group name="" purpose="location">
          <context context-type="sourcefile">../../exercises/tcp-2.rst</context>
          <context context-type="linenumber">105</context>
        </context-group>
      </trans-unit>
      <trans-unit xml:space="preserve" approved="no" id="0ff0cc560cbfced3" weblate-flags="read-only">
        <source>packetdrill_ writes 10 bytes of data through the :manpage:`write` system call. The stack immediately sends these 10 bytes inside a segment whose ``Push`` flag is set [#fpush]_. The payload starts at sequence number ``1`` and ends at sequence number ``10``. packetdrill_ replies by injecting an acknowledgment for the entire data after 100 milliseconds.</source>
        <target state="translated">packetdrill_ writes 10 bytes of data through the :manpage:`write` system call. The stack immediately sends these 10 bytes inside a segment whose ``Push`` flag is set [#fpush]_. The payload starts at sequence number ``1`` and ends at sequence number ``10``. packetdrill_ replies by injecting an acknowledgment for the entire data after 100 milliseconds.</target>
        <context-group name="" purpose="location">
          <context context-type="sourcefile">../../exercises/tcp-2.rst</context>
          <context context-type="linenumber">113</context>
        </context-group>
      </trans-unit>
      <trans-unit xml:space="preserve" approved="no" id="20a44bb8540e1277" weblate-flags="read-only">
        <source>packetdrill_ can also inject data that will be read by the stack as shown by the lines below.</source>
        <target state="translated">packetdrill_ can also inject data that will be read by the stack as shown by the lines below.</target>
        <context-group name="" purpose="location">
          <context context-type="sourcefile">../../exercises/tcp-2.rst</context>
          <context context-type="linenumber">115</context>
        </context-group>
      </trans-unit>
      <trans-unit xml:space="preserve" approved="no" id="297352691b65ce37" weblate-flags="read-only">
        <source>In the example above, packetdrill_ injects a segment containing two bytes. This segment is acknowledged and after that the :manpage:`read` system call succeeds and reads the available data with a buffer of 1000 bytes. It returns the amount of read bytes, i.e. ``2``.</source>
        <target state="translated">In the example above, packetdrill_ injects a segment containing two bytes. This segment is acknowledged and after that the :manpage:`read` system call succeeds and reads the available data with a buffer of 1000 bytes. It returns the amount of read bytes, i.e. ``2``.</target>
        <context-group name="" purpose="location">
          <context context-type="sourcefile">../../exercises/tcp-2.rst</context>
          <context context-type="linenumber">123</context>
        </context-group>
      </trans-unit>
      <trans-unit xml:space="preserve" approved="no" id="59933d89c5eba01e" weblate-flags="read-only">
        <source>We can now close the connection gracefully. Let us first issue inject a segment with the ``FIN`` flag set.</source>
        <target state="translated">We can now close the connection gracefully. Let us first issue inject a segment with the ``FIN`` flag set.</target>
        <context-group name="" purpose="location">
          <context context-type="sourcefile">../../exercises/tcp-2.rst</context>
          <context context-type="linenumber">125</context>
        </context-group>
      </trans-unit>
      <trans-unit xml:space="preserve" approved="no" id="ede0b2abcd1e37cb" weblate-flags="read-only">
        <source>packetdrill_ injects the ``FIN`` segment and the instrumented kernel returns an acknowledgment. If packetdrill_ issues the :manpage:`close` system call, the kernel will send a ``FIN`` segment to terminate the connection. packetdrill_ injects an acknowledgment to confirm the end of the connection.</source>
        <target state="translated">packetdrill_ injects the ``FIN`` segment and the instrumented kernel returns an acknowledgment. If packetdrill_ issues the :manpage:`close` system call, the kernel will send a ``FIN`` segment to terminate the connection. packetdrill_ injects an acknowledgment to confirm the end of the connection.</target>
        <context-group name="" purpose="location">
          <context context-type="sourcefile">../../exercises/tcp-2.rst</context>
          <context context-type="linenumber">133</context>
        </context-group>
      </trans-unit>
      <trans-unit xml:space="preserve" approved="no" id="f870049551f384aa" weblate-flags="read-only">
        <source>The complete packetdrill_ script is available from :download:`/exercises/packetdrill_scripts/connect.pkt`.</source>
        <target state="translated">The complete packetdrill_ script is available from :download:`/exercises/packetdrill_scripts/connect.pkt`.</target>
        <context-group name="" purpose="location">
          <context context-type="sourcefile">../../exercises/tcp-2.rst</context>
          <context context-type="linenumber">142</context>
        </context-group>
      </trans-unit>
      <trans-unit xml:space="preserve" approved="no" id="eb038fbd29438811" weblate-flags="read-only">
        <source>Another interesting features of packetdrill_ is that it is possible to inspect the state maintained by the Linux kernel for the underlying connection using the ``TCP_INFO`` socket option. This makes it possible to retrieve the value of some variables of the TCP control block.</source>
        <target state="translated">Another interesting features of packetdrill_ is that it is possible to inspect the state maintained by the Linux kernel for the underlying connection using the ``TCP_INFO`` socket option. This makes it possible to retrieve the value of some variables of the TCP control block.</target>
        <context-group name="" purpose="location">
          <context context-type="sourcefile">../../exercises/tcp-2.rst</context>
          <context context-type="linenumber">145</context>
        </context-group>
      </trans-unit>
      <trans-unit xml:space="preserve" approved="no" id="cd1a40b93802e42e" weblate-flags="read-only">
        <source>Let us first explore how a TCP connection can be established. In the previous script, we have injected the segments that a client would send to a server. We can also use the Linux stack as a client and inject the segments that a server would return. Such a client process would first create its :manpage:`socket`` and then issue the :manpage:`connect` system call. At this point, the stack sends a ``SYN`` segment. To simplify the scripts, we have configured the stack to use a ``MSS`` of 1000 bytes and disabled the TCP extensions (the details of this configuration may be found at the beginning of the script). The server replies with a ``SYN+ACK`` and the stack sends acknowledges it to finish the three-way-handshake.</source>
        <target state="translated">Let us first explore how a TCP connection can be established. In the previous script, we have injected the segments that a client would send to a server. We can also use the Linux stack as a client and inject the segments that a server would return. Such a client process would first create its :manpage:`socket`` and then issue the :manpage:`connect` system call. At this point, the stack sends a ``SYN`` segment. To simplify the scripts, we have configured the stack to use a ``MSS`` of 1000 bytes and disabled the TCP extensions (the details of this configuration may be found at the beginning of the script). The server replies with a ``SYN+ACK`` and the stack sends acknowledges it to finish the three-way-handshake.</target>
        <context-group name="" purpose="location">
          <context context-type="sourcefile">../../exercises/tcp-2.rst</context>
          <context context-type="linenumber">147</context>
        </context-group>
      </trans-unit>
      <trans-unit xml:space="preserve" approved="no" id="019ea2e08f0fe148" weblate-flags="read-only">
        <source>The ``tcpi_state`` variable used in this script is returned by ``TCP_INFO`` [#ftcpinfo]_. It tracks the state of the TCP connection according to TCP's finite state machine [#fstates]_. This script is available from :download:`/exercises/packetdrill_scripts/client.pkt`.</source>
        <target state="translated">The ``tcpi_state`` variable used in this script is returned by ``TCP_INFO`` [#ftcpinfo]_. It tracks the state of the TCP connection according to TCP's finite state machine [#fstates]_. This script is available from :download:`/exercises/packetdrill_scripts/client.pkt`.</target>
        <context-group name="" purpose="location">
          <context context-type="sourcefile">../../exercises/tcp-2.rst</context>
          <context context-type="linenumber">165</context>
        </context-group>
      </trans-unit>
      <trans-unit xml:space="preserve" approved="no" id="4fec6bed7e693c38" weblate-flags="read-only">
        <source>Another example is the simultaneous establishment of a TCP connection. The TCP stack sends a ``SYN`` and receives a ``SYN`` in response instead of a ``SYN+ACK``. It then acknowledges the received ``SYN`` and retransmits its own ``SYN``. The connection becomes established upon reception of the fourth segment. This script is available from :download:`/exercises/packetdrill_scripts/dual.pkt`.</source>
        <target state="translated">Another example is the simultaneous establishment of a TCP connection. The TCP stack sends a ``SYN`` and receives a ``SYN`` in response instead of a ``SYN+ACK``. It then acknowledges the received ``SYN`` and retransmits its own ``SYN``. The connection becomes established upon reception of the fourth segment. This script is available from :download:`/exercises/packetdrill_scripts/dual.pkt`.</target>
        <context-group name="" purpose="location">
          <context context-type="sourcefile">../../exercises/tcp-2.rst</context>
          <context context-type="linenumber">167</context>
        </context-group>
      </trans-unit>
      <trans-unit xml:space="preserve" approved="no" id="5e91985786490fd4" weblate-flags="read-only">
        <source>Another usage of packetdrill_ is to explore how a TCP connection ends. The scripts below show how a TCP stack closes a TCP connection. The first example shows a local host that connects to a remote host and then closes the connection. The remote host acknowledges the ``FIN`` and later closes its direction of data transfer. This script is available from :download:`/exercises/packetdrill_scripts/local-close.pkt`.</source>
        <target state="translated">Another usage of packetdrill_ is to explore how a TCP connection ends. The scripts below show how a TCP stack closes a TCP connection. The first example shows a local host that connects to a remote host and then closes the connection. The remote host acknowledges the ``FIN`` and later closes its direction of data transfer. This script is available from :download:`/exercises/packetdrill_scripts/local-close.pkt`.</target>
        <context-group name="" purpose="location">
          <context context-type="sourcefile">../../exercises/tcp-2.rst</context>
          <context context-type="linenumber">191</context>
        </context-group>
      </trans-unit>
      <trans-unit xml:space="preserve" approved="no" id="1f1f516d0658ac27" weblate-flags="read-only">
        <source>As for the establishment of a connection, it is also possible for the two communicating hosts to close the connection at the same time. This is shown in the example below where the remote host sends its own ``FIN`` when acknowledging the first one. This script is available from :download:`/exercises/packetdrill_scripts/local-close2.pkt`.</source>
        <target state="translated">As for the establishment of a connection, it is also possible for the two communicating hosts to close the connection at the same time. This is shown in the example below where the remote host sends its own ``FIN`` when acknowledging the first one. This script is available from :download:`/exercises/packetdrill_scripts/local-close2.pkt`.</target>
        <context-group name="" purpose="location">
          <context context-type="sourcefile">../../exercises/tcp-2.rst</context>
          <context context-type="linenumber">213</context>
        </context-group>
      </trans-unit>
      <trans-unit xml:space="preserve" approved="no" id="c2a944d734a0cf5a" weblate-flags="read-only">
        <source>A third scenario for the termination of a TCP connection is that the remote hosts sends its ``FIN`` first. This script is available from :download:`/exercises/packetdrill_scripts/remote-close.pkt`.</source>
        <target state="translated">A third scenario for the termination of a TCP connection is that the remote hosts sends its ``FIN`` first. This script is available from :download:`/exercises/packetdrill_scripts/remote-close.pkt`.</target>
        <context-group name="" purpose="location">
          <context context-type="sourcefile">../../exercises/tcp-2.rst</context>
          <context context-type="linenumber">234</context>
        </context-group>
      </trans-unit>
      <trans-unit xml:space="preserve" approved="no" id="c5c457ea0b471a5f" weblate-flags="read-only">
        <source>Another very interesting utilization of packetdrill_ is to explore how a TCP stack reacts to acknowledgments that would correspond to lost or reordered segments. For this analysis, we configure a very large initial congestion window to ensure that the connection does not start with a slow-start.</source>
        <target state="translated">Another very interesting utilization of packetdrill_ is to explore how a TCP stack reacts to acknowledgments that would correspond to lost or reordered segments. For this analysis, we configure a very large initial congestion window to ensure that the connection does not start with a slow-start.</target>
        <context-group name="" purpose="location">
          <context context-type="sourcefile">../../exercises/tcp-2.rst</context>
          <context context-type="linenumber">259</context>
        </context-group>
      </trans-unit>
      <trans-unit xml:space="preserve" approved="no" id="fac0947668cfde0a" weblate-flags="read-only">
        <source>Let us first use packetdrill_ to explore the evolution of the TCP retransmission timeout. The value of this timeout is set based on the measured round-trip-time and its variance. When the retransmission timer expires, TCP doubles the retransmission timer. This exponential backoff mechanism is important to ensure that TCP slowdowns during very severe congestion periods. We use the ``tcpi_rto`` variable from ``TCP_INFO`` to track the evolution of the retransmission timer. This script is available from :download:`/exercises/packetdrill_scripts/rto.pkt`.</source>
        <target state="translated">Let us first use packetdrill_ to explore the evolution of the TCP retransmission timeout. The value of this timeout is set based on the measured round-trip-time and its variance. When the retransmission timer expires, TCP doubles the retransmission timer. This exponential backoff mechanism is important to ensure that TCP slowdowns during very severe congestion periods. We use the ``tcpi_rto`` variable from ``TCP_INFO`` to track the evolution of the retransmission timer. This script is available from :download:`/exercises/packetdrill_scripts/rto.pkt`.</target>
        <context-group name="" purpose="location">
          <context context-type="sourcefile">../../exercises/tcp-2.rst</context>
          <context context-type="linenumber">261</context>
        </context-group>
      </trans-unit>
      <trans-unit xml:space="preserve" approved="no" id="ae42efcb1ded7baa" weblate-flags="read-only">
        <source>We can use a similar code to demonstrate that the TCP stack performs a fast retransmit after having received three duplicate acknowledgments. This script is available from :download:`/exercises/packetdrill_scripts/frr.pkt`.</source>
        <target state="translated">We can use a similar code to demonstrate that the TCP stack performs a fast retransmit after having received three duplicate acknowledgments. This script is available from :download:`/exercises/packetdrill_scripts/frr.pkt`.</target>
        <context-group name="" purpose="location">
          <context context-type="sourcefile">../../exercises/tcp-2.rst</context>
          <context context-type="linenumber">293</context>
        </context-group>
      </trans-unit>
      <trans-unit xml:space="preserve" approved="no" id="4acd2f48ffb7d0fb" weblate-flags="read-only">
        <source>A TCP stack uses both the fast retransmit technique and retransmission timers. A retransmission timer can fire after a fast retransmit when several segments are lost. The example below shows a loss of two consecutive segments. This script is available from :download:`/exercises/packetdrill_scripts/frr-rto.pkt`.</source>
        <target state="translated">A TCP stack uses both the fast retransmit technique and retransmission timers. A retransmission timer can fire after a fast retransmit when several segments are lost. The example below shows a loss of two consecutive segments. This script is available from :download:`/exercises/packetdrill_scripts/frr-rto.pkt`.</target>
        <context-group name="" purpose="location">
          <context context-type="sourcefile">../../exercises/tcp-2.rst</context>
          <context context-type="linenumber">326</context>
        </context-group>
      </trans-unit>
      <trans-unit xml:space="preserve" approved="no" id="61b5b3a2005548d0" weblate-flags="read-only">
        <source>More complex scenarios can be written. The script below demonstrates how the TCP stack behaves when three segments are lost. This script is available from :download:`/exercises/packetdrill_scripts/frr-rto2.pkt`.</source>
        <target state="translated">More complex scenarios can be written. The script below demonstrates how the TCP stack behaves when three segments are lost. This script is available from :download:`/exercises/packetdrill_scripts/frr-rto2.pkt`.</target>
        <context-group name="" purpose="location">
          <context context-type="sourcefile">../../exercises/tcp-2.rst</context>
          <context context-type="linenumber">364</context>
        </context-group>
      </trans-unit>
      <trans-unit xml:space="preserve" approved="no" id="cb9125e7c8a5aa14" weblate-flags="read-only">
        <source>The examples above have demonstrated how TCP retransmits lost segments. However, they did not consider the interactions with the congestion control scheme since the use a large initial congestion window. We now set the initial congestion window to two MSS-sized segments and use the ``tcpi_snd_cwnd`` and ``tcpi_snd_ssthresh`` variables from ``TCP_INFO`` to explore the evolution of the TCP congestion control scheme. Our first script looks at the evolution of the congestion window during a slow-start when there are no losses. This script is available from :download:`/exercises/packetdrill_scripts/slow-start.pkt`.</source>
        <target state="translated">The examples above have demonstrated how TCP retransmits lost segments. However, they did not consider the interactions with the congestion control scheme since the use a large initial congestion window. We now set the initial congestion window to two MSS-sized segments and use the ``tcpi_snd_cwnd`` and ``tcpi_snd_ssthresh`` variables from ``TCP_INFO`` to explore the evolution of the TCP congestion control scheme. Our first script looks at the evolution of the congestion window during a slow-start when there are no losses. This script is available from :download:`/exercises/packetdrill_scripts/slow-start.pkt`.</target>
        <context-group name="" purpose="location">
          <context context-type="sourcefile">../../exercises/tcp-2.rst</context>
          <context context-type="linenumber">411</context>
        </context-group>
      </trans-unit>
      <trans-unit xml:space="preserve" approved="no" id="bbd44947efb83a66" weblate-flags="read-only">
        <source>Some TCP clients use delayed acknowledgments and send a TCP acknowledgment after after second in-sequence segment. This behavior is illustrated in the script below. This script is available from :download:`/exercises/packetdrill_scripts/slow-start-delayed.pkt`.</source>
        <target state="translated">Some TCP clients use delayed acknowledgments and send a TCP acknowledgment after after second in-sequence segment. This behavior is illustrated in the script below. This script is available from :download:`/exercises/packetdrill_scripts/slow-start-delayed.pkt`.</target>
        <context-group name="" purpose="location">
          <context context-type="sourcefile">../../exercises/tcp-2.rst</context>
          <context context-type="linenumber">459</context>
        </context-group>
      </trans-unit>
      <trans-unit xml:space="preserve" approved="no" id="c1e367d8e89cdc25" weblate-flags="read-only">
        <source>We can now explore how TCP's retransmission techniques interact with the congestion control scheme. The Linux TCP code that combines these two techniques contains several heuristics to improve their performance. We start with a transfer of 8KBytes where the penultimate segment is not received by the remote host. In this case, TCP does not receive enough acknowledgments to trigger the fast retransmit and it must wait for the expiration of the retransmission timer. This script is available from :download:`/exercises/packetdrill_scripts/slow-start-rto2.pkt`.</source>
        <target state="translated">We can now explore how TCP's retransmission techniques interact with the congestion control scheme. The Linux TCP code that combines these two techniques contains several heuristics to improve their performance. We start with a transfer of 8KBytes where the penultimate segment is not received by the remote host. In this case, TCP does not receive enough acknowledgments to trigger the fast retransmit and it must wait for the expiration of the retransmission timer. This script is available from :download:`/exercises/packetdrill_scripts/slow-start-rto2.pkt`.</target>
        <context-group name="" purpose="location">
          <context context-type="sourcefile">../../exercises/tcp-2.rst</context>
          <context context-type="linenumber">502</context>
        </context-group>
      </trans-unit>
      <trans-unit xml:space="preserve" approved="no" id="4620b31fc05793e7" weblate-flags="read-only">
        <source>Another interesting scenario is when the loss happens early in the data transfer. This is shown in the script below where the second segment is lost. We observe that by triggering transmissions of unacknowledged data, the :rfc:`3042` rule speeds up the recovery since a fast retransmit happens. This script is available from :download:`/exercises/packetdrill_scripts/slow-start-frr2.pkt`.</source>
        <target state="translated">Another interesting scenario is when the loss happens early in the data transfer. This is shown in the script below where the second segment is lost. We observe that by triggering transmissions of unacknowledged data, the :rfc:`3042` rule speeds up the recovery since a fast retransmit happens. This script is available from :download:`/exercises/packetdrill_scripts/slow-start-frr2.pkt`.</target>
        <context-group name="" purpose="location">
          <context context-type="sourcefile">../../exercises/tcp-2.rst</context>
          <context context-type="linenumber">546</context>
        </context-group>
      </trans-unit>
      <trans-unit xml:space="preserve" approved="no" id="f9c1ed124553d248" weblate-flags="read-only">
        <source>Our last scenario is when the first segment sent is lost. In this case, two round-trip-times are required to retransmit the missing segment and recover from the loss. This script is available from :download:`/exercises/packetdrill_scripts/slow-start-frr3.pkt`.</source>
        <target state="translated">Our last scenario is when the first segment sent is lost. In this case, two round-trip-times are required to retransmit the missing segment and recover from the loss. This script is available from :download:`/exercises/packetdrill_scripts/slow-start-frr3.pkt`.</target>
        <context-group name="" purpose="location">
          <context context-type="sourcefile">../../exercises/tcp-2.rst</context>
          <context context-type="linenumber">593</context>
        </context-group>
      </trans-unit>
      <trans-unit xml:space="preserve" approved="no" id="ea725087c218738b" weblate-flags="read-only">
        <source>Open questions</source>
        <target state="translated">Open questions</target>
        <context-group name="" purpose="location">
          <context context-type="sourcefile">../../exercises/tcp-2.rst</context>
          <context context-type="linenumber">637</context>
        </context-group>
      </trans-unit>
      <trans-unit xml:space="preserve" approved="no" id="da3663d4a6a0c09a" weblate-flags="read-only">
        <source>Unless otherwise noted, we assume for the questions in this section that the following conditions hold.</source>
        <target state="translated">Unless otherwise noted, we assume for the questions in this section that the following conditions hold.</target>
        <context-group name="" purpose="location">
          <context context-type="sourcefile">../../exercises/tcp-2.rst</context>
          <context context-type="linenumber">639</context>
        </context-group>
      </trans-unit>
      <trans-unit xml:space="preserve" approved="no" id="9a2c69988dd89da5" weblate-flags="read-only">
        <source>the sender/receiver performs a single :manpage:`send(3)` of `x` bytes</source>
        <target state="translated">the sender/receiver performs a single :manpage:`send(3)` of `x` bytes</target>
        <context-group name="" purpose="location">
          <context context-type="sourcefile">../../exercises/tcp-2.rst</context>
          <context context-type="linenumber">641</context>
        </context-group>
      </trans-unit>
      <trans-unit xml:space="preserve" approved="no" id="e069e6262abe9e91" weblate-flags="read-only">
        <source>the round-trip-time is fixed and does not change during the lifetime of the TCP connection. We assume a fixed value of 100 milliseconds for the round-trip-time and a fixed value of 200 milliseconds for the retransmission timer.</source>
        <target state="translated">the round-trip-time is fixed and does not change during the lifetime of the TCP connection. We assume a fixed value of 100 milliseconds for the round-trip-time and a fixed value of 200 milliseconds for the retransmission timer.</target>
        <context-group name="" purpose="location">
          <context context-type="sourcefile">../../exercises/tcp-2.rst</context>
          <context context-type="linenumber">642</context>
        </context-group>
      </trans-unit>
      <trans-unit xml:space="preserve" approved="no" id="c9fcbf2e0e15709d" weblate-flags="read-only">
        <source>the delay required to transmit a single TCP segment containing MSS bytes is small and set to 1 milliseconds, independently of the MSS size</source>
        <target state="translated">the delay required to transmit a single TCP segment containing MSS bytes is small and set to 1 milliseconds, independently of the MSS size</target>
        <context-group name="" purpose="location">
          <context context-type="sourcefile">../../exercises/tcp-2.rst</context>
          <context context-type="linenumber">643</context>
        </context-group>
      </trans-unit>
      <trans-unit xml:space="preserve" approved="no" id="9152f05d6688781c" weblate-flags="read-only">
        <source>the transmission delay for a TCP acknowledgment is negligible</source>
        <target state="translated">the transmission delay for a TCP acknowledgment is negligible</target>
        <context-group name="" purpose="location">
          <context context-type="sourcefile">../../exercises/tcp-2.rst</context>
          <context context-type="linenumber">644</context>
        </context-group>
      </trans-unit>
      <trans-unit xml:space="preserve" approved="no" id="dc9d2e2a59448864" weblate-flags="read-only">
        <source>the initial value of the congestion window is one MSS-sized segment</source>
        <target state="translated">the initial value of the congestion window is one MSS-sized segment</target>
        <context-group name="" purpose="location">
          <context context-type="sourcefile">../../exercises/tcp-2.rst</context>
          <context context-type="linenumber">645</context>
        </context-group>
      </trans-unit>
      <trans-unit xml:space="preserve" approved="no" id="c23bb1e0f3a10ef0" weblate-flags="read-only">
        <source>the value of the duplicate acknowledgment threshold is fixed and set to 3</source>
        <target state="translated">the value of the duplicate acknowledgment threshold is fixed and set to 3</target>
        <context-group name="" purpose="location">
          <context context-type="sourcefile">../../exercises/tcp-2.rst</context>
          <context context-type="linenumber">646</context>
        </context-group>
      </trans-unit>
      <trans-unit xml:space="preserve" approved="no" id="0564800c56ec6e68" weblate-flags="read-only">
        <source>TCP always acknowledges each received segment</source>
        <target state="translated">TCP always acknowledges each received segment</target>
        <context-group name="" purpose="location">
          <context context-type="sourcefile">../../exercises/tcp-2.rst</context>
          <context context-type="linenumber">647</context>
        </context-group>
      </trans-unit>
      <trans-unit xml:space="preserve" approved="no" id="65c49b93d64d79ac" weblate-flags="read-only">
        <source>To understand the operation of the TCP congestion control, it is often useful to write time-sequence diagrams for different scenarios. The example below shows the operation of the TCP congestion control scheme in a very simple scenario. The initial congestion window (``cwnd``) is set to 1000 bytes and the receive window (``rwin``) advertised by the receiver (supposed constant for the entire connection) is set to 2000 bytes. The slow-start threshold (``ssthresh``) is set to 64000 bytes.</source>
        <target state="translated">To understand the operation of the TCP congestion control, it is often useful to write time-sequence diagrams for different scenarios. The example below shows the operation of the TCP congestion control scheme in a very simple scenario. The initial congestion window (``cwnd``) is set to 1000 bytes and the receive window (``rwin``) advertised by the receiver (supposed constant for the entire connection) is set to 2000 bytes. The slow-start threshold (``ssthresh``) is set to 64000 bytes.</target>
        <context-group name="" purpose="location">
          <context context-type="sourcefile">../../exercises/tcp-2.rst</context>
          <context context-type="linenumber">649</context>
        </context-group>
      </trans-unit>
      <trans-unit xml:space="preserve" approved="no" id="c5d203bdb79642b5" weblate-flags="read-only">
        <source>Can you explain why the sender only sends one segment first and then two successive segments (the delay between the two segments on the figure is due to graphical reasons) ?</source>
        <target state="translated">Can you explain why the sender only sends one segment first and then two successive segments (the delay between the two segments on the figure is due to graphical reasons) ?</target>
        <context-group name="" purpose="location">
          <context context-type="sourcefile">../../exercises/tcp-2.rst</context>
          <context context-type="linenumber">684</context>
        </context-group>
      </trans-unit>
      <trans-unit xml:space="preserve" approved="no" id="b3676e63798cb6db" weblate-flags="read-only">
        <source>Can you explain why the congestion window is increased after the reception of the first acknowledgment ?</source>
        <target state="translated">Can you explain why the congestion window is increased after the reception of the first acknowledgment ?</target>
        <context-group name="" purpose="location">
          <context context-type="sourcefile">../../exercises/tcp-2.rst</context>
          <context context-type="linenumber">686</context>
        </context-group>
      </trans-unit>
      <trans-unit xml:space="preserve" approved="no" id="3370a4decd7f72f0" weblate-flags="read-only">
        <source>How long does it take for the sender to deliver 3 KBytes to the receiver ?</source>
        <target state="translated">How long does it take for the sender to deliver 3 KBytes to the receiver ?</target>
        <context-group name="" purpose="location">
          <context context-type="sourcefile">../../exercises/tcp-2.rst</context>
          <context context-type="linenumber">688</context>
        </context-group>
      </trans-unit>
      <trans-unit xml:space="preserve" approved="no" id="4773b4ecee6580f2" weblate-flags="read-only">
        <source>Same question as above but now with a small variation. Recent TCP implementations use a large initial value for the congestion window. Draw the time-sequence diagram that corresponds to an initial value of 10000 bytes for this congestion window.</source>
        <target state="translated">Same question as above but now with a small variation. Recent TCP implementations use a large initial value for the congestion window. Draw the time-sequence diagram that corresponds to an initial value of 10000 bytes for this congestion window.</target>
        <context-group name="" purpose="location">
          <context context-type="sourcefile">../../exercises/tcp-2.rst</context>
          <context context-type="linenumber">691</context>
        </context-group>
      </trans-unit>
      <trans-unit xml:space="preserve" approved="no" id="e17a3e513c2cf7e2" weblate-flags="read-only">
        <source>Same question as the first one, but consider that the MSS on the sender is set to 500 bytes. How does this modification affect the entire delay ?</source>
        <target state="translated">Same question as the first one, but consider that the MSS on the sender is set to 500 bytes. How does this modification affect the entire delay ?</target>
        <context-group name="" purpose="location">
          <context context-type="sourcefile">../../exercises/tcp-2.rst</context>
          <context context-type="linenumber">715</context>
        </context-group>
      </trans-unit>
      <trans-unit xml:space="preserve" approved="no" id="694c451ae089c99c" weblate-flags="read-only">
        <source>Assuming that there are no losses and that there is no congestion in the network. If the sender writes `x` bytes on a newly established TCP connection, derive a formula that computes the minimum time required to deliver all these `x` bytes to the receiver. For the derivation of this formula, assume that `x` is a multiple of the maximum segment size and that the receive window and the slow-start threshold are larger than `x`.</source>
        <target state="translated">Assuming that there are no losses and that there is no congestion in the network. If the sender writes `x` bytes on a newly established TCP connection, derive a formula that computes the minimum time required to deliver all these `x` bytes to the receiver. For the derivation of this formula, assume that `x` is a multiple of the maximum segment size and that the receive window and the slow-start threshold are larger than `x`.</target>
        <context-group name="" purpose="location">
          <context context-type="sourcefile">../../exercises/tcp-2.rst</context>
          <context context-type="linenumber">738</context>
        </context-group>
      </trans-unit>
      <trans-unit xml:space="preserve" approved="no" id="382d6e212200c119" weblate-flags="read-only">
        <source>In question 1, we assumed that the receiver acknowledged every segment received from the sender. In practice, many deployed TCP implementations use delayed acknowledgments. Assuming a delayed acknowledgment timer of 50 milliseconds, modify the time-sequence diagram below to reflect the impact of these delayed acknowledgment. Does their usage decreases or increased the transmission delay ?</source>
        <target state="translated">In question 1, we assumed that the receiver acknowledged every segment received from the sender. In practice, many deployed TCP implementations use delayed acknowledgments. Assuming a delayed acknowledgment timer of 50 milliseconds, modify the time-sequence diagram below to reflect the impact of these delayed acknowledgment. Does their usage decreases or increased the transmission delay ?</target>
        <context-group name="" purpose="location">
          <context context-type="sourcefile">../../exercises/tcp-2.rst</context>
          <context context-type="linenumber">740</context>
        </context-group>
      </trans-unit>
      <trans-unit xml:space="preserve" approved="no" id="5966374a1cb6dc04" weblate-flags="read-only">
        <source>Let us now explore the impact of congestion on the slow-start and congestion avoidance mechanisms. Consider the scenario below. For graphical reasons, it is not possible anymore to show information about the segments on the graph, but you can easily infer them.</source>
        <target state="translated">Let us now explore the impact of congestion on the slow-start and congestion avoidance mechanisms. Consider the scenario below. For graphical reasons, it is not possible anymore to show information about the segments on the graph, but you can easily infer them.</target>
        <context-group name="" purpose="location">
          <context context-type="sourcefile">../../exercises/tcp-2.rst</context>
          <context context-type="linenumber">775</context>
        </context-group>
      </trans-unit>
      <trans-unit xml:space="preserve" approved="no" id="cfc3d671a36fe12d" weblate-flags="read-only">
        <source>Redraw the same figure assuming that the second segment that was delivered by the sender in the figure experienced congestion. In a network that uses Explicit Congestion Notification, this segment would be marked by routers and the receiver would return the congestion mark in the corresponding acknowledgment.</source>
        <target state="translated">Redraw the same figure assuming that the second segment that was delivered by the sender in the figure experienced congestion. In a network that uses Explicit Congestion Notification, this segment would be marked by routers and the receiver would return the congestion mark in the corresponding acknowledgment.</target>
        <context-group name="" purpose="location">
          <context context-type="sourcefile">../../exercises/tcp-2.rst</context>
          <context context-type="linenumber">832</context>
        </context-group>
      </trans-unit>
      <trans-unit xml:space="preserve" approved="no" id="9240346c4c40f95d" weblate-flags="read-only">
        <source>Same question, but assume now that the fourth segment delivered by the sender experienced congestion (but was not discarded).</source>
        <target state="translated">Same question, but assume now that the fourth segment delivered by the sender experienced congestion (but was not discarded).</target>
        <context-group name="" purpose="location">
          <context context-type="sourcefile">../../exercises/tcp-2.rst</context>
          <context context-type="linenumber">834</context>
        </context-group>
      </trans-unit>
      <trans-unit xml:space="preserve" approved="no" id="97d890bb222975ff" weblate-flags="read-only">
        <source>A TCP connection has been active for some time and has reached a congestion window of 4000 bytes. Four segments are sent, but the second (shown in red in the figure) is corrupted. Complete the time-sequence diagram.</source>
        <target state="translated">A TCP connection has been active for some time and has reached a congestion window of 4000 bytes. Four segments are sent, but the second (shown in red in the figure) is corrupted. Complete the time-sequence diagram.</target>
        <context-group name="" purpose="location">
          <context context-type="sourcefile">../../exercises/tcp-2.rst</context>
          <context context-type="linenumber">837</context>
        </context-group>
      </trans-unit>
      <trans-unit xml:space="preserve" approved="no" id="c463aea6549199a2" weblate-flags="read-only">
        <source>Footnotes</source>
        <target state="translated">Footnotes</target>
        <context-group name="" purpose="location">
          <context context-type="sourcefile">../../exercises/tcp-2.rst</context>
          <context context-type="linenumber">871</context>
        </context-group>
      </trans-unit>
      <trans-unit xml:space="preserve" approved="no" id="b73769b34f5c01c7" weblate-flags="read-only">
        <source>On Linux, most of the parameters to tune the TCP stack are accessible via :manpage:`sysctl`. These parameters are briefly described in https://github.com/torvalds/linux/blob/master/Documentation/networking/ip-sysctl.txt and in the :manpage:`tcp` manpage. Each script sets some of these configuration variables.</source>
        <target state="translated">On Linux, most of the parameters to tune the TCP stack are accessible via :manpage:`sysctl`. These parameters are briefly described in https://github.com/torvalds/linux/blob/master/Documentation/networking/ip-sysctl.txt and in the :manpage:`tcp` manpage. Each script sets some of these configuration variables.</target>
        <context-group name="" purpose="location">
          <context context-type="sourcefile">../../exercises/tcp-2.rst</context>
          <context context-type="linenumber">876</context>
        </context-group>
      </trans-unit>
      <trans-unit xml:space="preserve" approved="no" id="806e185503c12354" weblate-flags="read-only">
        <source>packetdrill_ requires root privileges since it inject raw IP packets. The easiest way to install it is to use a virtualbox image with a Linux kernel 4.x or 5.x. You can clone its git repository from https://github.com/google/packetdrill and follow the instructions in https://github.com/google/packetdrill/tree/master/gtests/net/packetdrill. The packetdrill_ scripts used in this section are available from https://github.com/cnp3/ebook/tree/master/exercises/packetdrill_scripts</source>
        <target state="translated">packetdrill_ requires root privileges since it inject raw IP packets. The easiest way to install it is to use a virtualbox image with a Linux kernel 4.x or 5.x. You can clone its git repository from https://github.com/google/packetdrill and follow the instructions in https://github.com/google/packetdrill/tree/master/gtests/net/packetdrill. The packetdrill_ scripts used in this section are available from https://github.com/cnp3/ebook/tree/master/exercises/packetdrill_scripts</target>
        <context-group name="" purpose="location">
          <context context-type="sourcefile">../../exercises/tcp-2.rst</context>
          <context context-type="linenumber">883</context>
        </context-group>
      </trans-unit>
      <trans-unit xml:space="preserve" approved="no" id="353a97e81ab93f72" weblate-flags="read-only">
        <source>By default, packetdrill_ uses port 8080 when creating TCP segments. You can thus capture the packets injected by packetdrill_ and the responses from the stack by using ``tcpdump -i any -n port 8080``</source>
        <target state="translated">By default, packetdrill_ uses port 8080 when creating TCP segments. You can thus capture the packets injected by packetdrill_ and the responses from the stack by using ``tcpdump -i any -n port 8080``</target>
        <context-group name="" purpose="location">
          <context context-type="sourcefile">../../exercises/tcp-2.rst</context>
          <context context-type="linenumber">885</context>
        </context-group>
      </trans-unit>
      <trans-unit xml:space="preserve" approved="no" id="3f2a8b2864a21f26" weblate-flags="read-only">
        <source>The `Push` flag is one of the TCP flags defined in :rfc:`793`. TCP stacks usually set this flag when transmitting a segment that empties the send buffer. This is the reason why we observe this push flag in our example.</source>
        <target state="translated">The `Push` flag is one of the TCP flags defined in :rfc:`793`. TCP stacks usually set this flag when transmitting a segment that empties the send buffer. This is the reason why we observe this push flag in our example.</target>
        <context-group name="" purpose="location">
          <context context-type="sourcefile">../../exercises/tcp-2.rst</context>
          <context context-type="linenumber">887</context>
        </context-group>
      </trans-unit>
      <trans-unit xml:space="preserve" approved="no" id="8ea774d17e701c9a" weblate-flags="read-only">
        <source>The variables that are included in TCP_INFO are defined in https://github.com/torvalds/linux/blob/master/include/uapi/linux/tcp.h</source>
        <target state="translated">The variables that are included in TCP_INFO are defined in https://github.com/torvalds/linux/blob/master/include/uapi/linux/tcp.h</target>
        <context-group name="" purpose="location">
          <context context-type="sourcefile">../../exercises/tcp-2.rst</context>
          <context context-type="linenumber">889</context>
        </context-group>
      </trans-unit>
      <trans-unit xml:space="preserve" approved="no" id="83300c70aa5fa299" weblate-flags="read-only">
        <source>These states are defined in https://github.com/torvalds/linux/blob/master/include/net/tcp_states.h</source>
        <target state="translated">These states are defined in https://github.com/torvalds/linux/blob/master/include/net/tcp_states.h</target>
        <context-group name="" purpose="location">
          <context context-type="sourcefile">../../exercises/tcp-2.rst</context>
          <context context-type="linenumber">891</context>
        </context-group>
      </trans-unit>
    </body>
  </file>
</xliff>
