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<h1 id="firstHeading" class="firstHeading mw-first-heading"><span class="mw-page-title-main">DCF Interframe Space</span></h1>
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<div id="mw-content-text" class="mw-body-content mw-content-ltr" lang="fr" dir="ltr"><div class="mw-content-ltr mw-parser-output" lang="fr" dir="ltr"><p>Le <b>DCF Interframe Space (DIFS)</b> est l'un des intervalles inter-trames utilisé par les réseaux <a href="R%C3%A9seau_sans_fil" title="Réseau sans fil">WLAN</a> de la norme <a href="IEEE_802.11" title="IEEE 802.11">IEEE 802.11</a>. Une station ayant activé le <a href="Distributed_Coordination_Function" title="Distributed Coordination Function">DCF</a> doit sonder le medium pendant une durée d'un DIFS. Si pendant cet intervalle, aucun trafic n'est détecté, la station est autorisée à transmettre. Sinon, elle doit reporter sa transmission. Cet intervalle fait partie de la méthode d'accès <a href="Carrier_Sense_Multiple_Access_with_Collision_Avoidance" title="Carrier Sense Multiple Access with Collision Avoidance">CSMA/CA</a> qui permet de partager un réseau 802.11 (<a href="Wi-Fi" title="Wi-Fi">Wi-Fi</a>) entre plusieurs stations.
</p><p>Le DIFS peut être calculé de la manière suivante :
</p><p><span class="mwe-math-element mwe-math-element-inline"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle \mathrm {DIFS} =}">
<semantics>
<mrow class="MJX-TeXAtom-ORD">
<mstyle displaystyle="true" scriptlevel="0">
<mrow class="MJX-TeXAtom-ORD">
<mi mathvariant="normal">D</mi>
<mi mathvariant="normal">I</mi>
<mi mathvariant="normal">F</mi>
<mi mathvariant="normal">S</mi>
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<mo>=</mo>
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<annotation encoding="application/x-tex">{\displaystyle \mathrm {DIFS} =}</annotation>
</semantics>
</math></span><img src="./_assets_/eb734a37dd21ce173a46342d1cc64c92/5f35660bf174377fee4260a2efe591c637e41e5d.svg" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.338ex; width:7.879ex; height:2.176ex;" alt="{\displaystyle \mathrm {DIFS} =}" loading="lazy"></span><a href="Intervalle_inter-trame_court" title="Intervalle inter-trame court"> <span class="mwe-math-element mwe-math-element-inline"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle \color {Blue}\mathrm {SIFS} }">
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<mrow class="MJX-TeXAtom-ORD">
<mstyle displaystyle="true" scriptlevel="0">
<mstyle mathcolor="#2D2F92">
<mrow class="MJX-TeXAtom-ORD">
<mi mathvariant="normal">S</mi>
<mi mathvariant="normal">I</mi>
<mi mathvariant="normal">F</mi>
<mi mathvariant="normal">S</mi>
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</mstyle>
</mstyle>
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<annotation encoding="application/x-tex">{\displaystyle \color {Blue}\mathrm {SIFS} }</annotation>
</semantics>
</math></span><img src="./_assets_/eb734a37dd21ce173a46342d1cc64c92/50bd2780383363059dd5e31df82b253b1a2d4437.svg" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.338ex; width:4.942ex; height:2.176ex;" alt="{\displaystyle \color {Blue}\mathrm {SIFS} }" loading="lazy"></span></a><span class="mwe-math-element mwe-math-element-inline"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle +(2\times {\text{Dur}}\mathrm {\acute {e}} {\text{e d'un slot}})}">
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<mrow class="MJX-TeXAtom-ORD">
<mstyle displaystyle="true" scriptlevel="0">
<mo>+</mo>
<mo stretchy="false">(</mo>
<mn>2</mn>
<mo>×<!-- × --></mo>
<mrow class="MJX-TeXAtom-ORD">
<mtext>Dur</mtext>
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<mrow class="MJX-TeXAtom-ORD">
<mrow class="MJX-TeXAtom-ORD">
<mover>
<mi mathvariant="normal">e</mi>
<mo>´<!-- ´ --></mo>
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<mrow class="MJX-TeXAtom-ORD">
<mtext>e d'un slot</mtext>
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<mo stretchy="false">)</mo>
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<annotation encoding="application/x-tex">{\displaystyle +(2\times {\text{Dur}}\mathrm {\acute {e}} {\text{e d'un slot}})}</annotation>
</semantics>
</math></span><img src="./_assets_/eb734a37dd21ce173a46342d1cc64c92/7025a92ceec6ff15b64a40cced822e532efe7ce0.svg" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.838ex; width:23.111ex; height:2.843ex;" alt="{\displaystyle +(2\times {\text{Dur}}\mathrm {\acute {e}} {\text{e d'un slot}})}" loading="lazy"></span> <sup id="cite_ref-1" class="reference"><a href="#cite_note-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup>
</p>
<table style="margin-bottom: 10px;" class="wikitable">
<tbody><tr>
<th>Standard
</th>
<th>Durée d'un slot (µs)
</th>
<th>DIFS (µs)
</th></tr>
<tr>
<td>IEEE 802.11-1997 (FHSS)
</td>
<td>50
</td>
<td>128
</td></tr>
<tr>
<td>IEEE 802.11-1997 (DSSS)
</td>
<td>20
</td>
<td>50
</td></tr>
<tr>
<td><a href="IEEE_802.11b" title="IEEE 802.11b">IEEE 802.11b</a>
</td>
<td>20
</td>
<td>50
</td></tr>
<tr>
<td><a href="IEEE_802.11a" title="IEEE 802.11a">IEEE 802.11a</a>
</td>
<td>9
</td>
<td>34
</td></tr>
<tr>
<td><a href="IEEE_802.11g" title="IEEE 802.11g">IEEE 802.11g</a>
</td>
<td>9 ou 20
</td>
<td>28 ou 50
</td></tr>
<tr>
<td><a href="IEEE_802.11n" title="IEEE 802.11n">IEEE 802.11n</a> (2.4 GHz)
</td>
<td>9 ou 20
</td>
<td>28 ou 50
</td></tr>
<tr>
<td><a href="IEEE_802.11n" title="IEEE 802.11n">IEEE 802.11n</a> (5 GHz)
</td>
<td>9
</td>
<td>34
</td></tr>
<tr>
<td><a href="IEEE_802.11ac" title="IEEE 802.11ac">IEEE 802.11ac</a> (5 GHz)
</td>
<td>9
</td>
<td>34
</td></tr></tbody></table>
<p>La norme <a href="IEEE_802.11g" title="IEEE 802.11g">IEEE 802.11g</a> est rétrocompatible avec la norme <a href="IEEE_802.11b" title="IEEE 802.11b">IEEE 802.11b</a>. Quand un appareil 802.11b est associé à un point d'accès 802.11g, les valeurs du DIFS changent pour celles de 802.11b.
</p>
<div class="mw-heading mw-heading2"><h2 id="Références"><span id="R.C3.A9f.C3.A9rences"></span>Références</h2></div>
<div class="references-small decimal" style=""><div class="mw-references-wrap"><ol class="references">
<li id="cite_note-1"><span class="mw-cite-backlink"><a href="#cite_ref-1">↑</a> </span><span class="reference-text"><a rel="nofollow" class="external text" href="http://standards.ieee.org/getieee802/download/802.11-2012.pdf">"IEEE 802.11 Standard"</a> (PDF), 2012, Page 843 of PDF</span>
</li>
</ol></div>
</div>
<div class="mw-heading mw-heading2"><h2 id="Voir_aussi">Voir aussi</h2></div>
<div class="mw-heading mw-heading3"><h3 id="Articles_connexes">Articles connexes</h3></div>
<ul><li>SIFS - <a href="Intervalle_inter-trame_court" title="Intervalle inter-trame court">Short Interframe Space</a></li>
<li>RIFS - <a href="Reduced_Interframe_Space" title="Reduced Interframe Space">Reduced Interframe Space</a></li>
<li>PIFS - <a href="PCF_Interframe_Space" title="PCF Interframe Space">PCF Interframe Space</a></li>
<li>EIFS - <a href="Extended_Interframe_Space" title="Extended Interframe Space">Extended Interframe Space</a></li>
<li>AIFS - <a href="Arbitration_Interframe_Space" title="Arbitration Interframe Space">Arbitration Interframe Space</a></li>
<li>PCF - <a href="Point_Coordinated_Function" title="Point Coordinated Function">Point Coordination Function</a></li>
<li>DCF - <a href="Distributed_Coordination_Function" title="Distributed Coordination Function">Distributed Coordination Function</a></li></ul>
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