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	<title>RMAODV 彙整 - 碼蟻創研工坊 - CODEANT STUDIOS</title>
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	<title>RMAODV 彙整 - 碼蟻創研工坊 - CODEANT STUDIOS</title>
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		<title>802.11s RMAODV 被動式路由協議(Mesh Routing Protocol)</title>
		<link>http://codeant.cc/archives/29</link>
		
		<dc:creator><![CDATA[codeant]]></dc:creator>
		<pubDate>Thu, 11 Jul 2013 01:02:52 +0000</pubDate>
				<category><![CDATA[Netowrk]]></category>
		<category><![CDATA[802.11s]]></category>
		<category><![CDATA[Mesh]]></category>
		<category><![CDATA[RMAODV]]></category>
		<category><![CDATA[路由協議]]></category>
		<guid isPermaLink="false">http://codeant.cc/2013/07/11/80211s-rmaodv-mesh-routing-protocol/</guid>

					<description><![CDATA[<p>802.11s RMAODV全名為Radio Metric Ad hoc On-Demand Distance [&#8230;]</p>
<p>這篇文章 <a href="http://codeant.cc/archives/29">802.11s RMAODV 被動式路由協議(Mesh Routing Protocol)</a> 最早出現於 <a href="http://codeant.cc">碼蟻創研工坊 - CODEANT STUDIOS</a>。</p>
]]></description>
										<content:encoded><![CDATA[<p style="text-indent: 24pt; line-height: 150%; text-align: left;"><span style="font-size: 16px; line-height: 26px;">802.11s RMAODV全名為Radio Metric Ad hoc On-Demand Distance Vector Radio，是一個運行在OSI第二層的網狀路由協議，屬於被動式的路由協議，採用距離向量的路由方法，是由目前使用率最高的被動式路由協議Ad hoc On-Demand Distance Vector（AODV）演化而來。</span></p>
<p>  <span id="more-29"></span>  </p>
<p style="font-size: 16px; line-height: 26px; text-align: left; text-indent: 24pt;"><span style="font-family: 'comic sans ms', sans-serif; font-size: 12pt;">不同的是在802.11s中PREQ封包有Target Only（TO）的旗標（flag）設定，所以在RMAODV協議中可以透過TO旗標設定成只有目的地可以回傳PREP，這是為了減少路由資訊封包在交換過程中所帶來的系統負擔，而AODV路由協議則是只要知道目的地的路徑的中間節點都可回傳PREP。</span></p>
<p style="font-size: 16px; line-height: 26px; text-align: left; text-indent: 24pt;"><span style="font-family: 'comic sans ms', sans-serif; font-size: 12pt;">802.11s其系統組成主要由下列三個裝置組成，其組成架構如圖:</span></p>
<p style="text-indent: 24pt; line-height: 150%; text-align: left;"><span style="font-size: 12pt; font-family: 'comic sans ms', sans-serif;">&nbsp;<img fetchpriority="high" decoding="async" class=" size-full wp-image-26" src="http://codeant.cc/wp-content/uploads/2013/07/images_phocagallery_Network_80211s-network-arch.jpg" alt="80211s-network-arch" width="491" height="382" style="display: block; margin-left: auto; margin-right: auto;" srcset="http://codeant.cc/wp-content/uploads/2013/07/images_phocagallery_Network_80211s-network-arch.jpg 491w, http://codeant.cc/wp-content/uploads/2013/07/images_phocagallery_Network_80211s-network-arch-300x233.jpg 300w" sizes="(max-width: 491px) 100vw, 491px" /></span></p>
<p style="font-size: 16px; line-height: 26px; text-align: left; text-indent: 24pt;"><span style="font-family: 'comic sans ms', sans-serif; font-size: 12pt;"></span></p>
<p style="font-size: 16px; line-height: 26px; text-align: left; text-indent: 24pt;"><span style="font-family: 'comic sans ms', sans-serif; font-size: 12pt;">1.<span style="line-height: normal;">&nbsp; &nbsp; &nbsp;</span><strong>Mesh Portal Point</strong><strong>（</strong><strong>MPP</strong><strong>）</strong>：具有網路閘道（Gateway）的功能，負責與外部網路連結，如網際網路（Internet）。</span></p>
<p style="font-size: 16px; line-height: 26px; text-align: left; text-indent: 24pt;"><span style="font-family: 'comic sans ms', sans-serif; font-size: 12pt;"></span></p>
<p style="font-size: 16px; line-height: 26px; text-align: left; text-indent: 24pt;"><span style="font-family: 'comic sans ms', sans-serif; font-size: 12pt;">2.<span style="line-height: normal;">&nbsp; &nbsp;&nbsp;</span><strong>Mesh Point</strong><strong>（</strong><strong>MP</strong><strong>）</strong>：此裝置負責了路由及資料轉發的功能，在同一個網狀網路基本服務組（Mesh Basic Service Set，簡稱MBSS）下，MP之間可以直接通信。</span></p>
<p style="font-size: 16px; line-height: 26px; text-align: left; text-indent: 24pt;"><span style="font-family: 'comic sans ms', sans-serif; font-size: 12pt;"></span></p>
<p style="font-size: 16px; line-height: 26px; text-align: left; text-indent: 24pt;"><span style="font-family: 'comic sans ms', sans-serif; font-size: 12pt;">3.<span style="line-height: normal;">&nbsp; &nbsp;&nbsp;</span><strong>Mesh Access Point</strong><strong>（</strong><strong>MAP</strong><strong>）</strong>：MAP負責與傳統的網路設備連接，並將資料轉送到MP，扮演MBSS與一般基本服務組（Basis Service Set，簡稱BSS）的中介橋梁。</span></p>
<p style="font-size: 16px; line-height: 26px; text-align: left; text-indent: 24pt;"><span style="font-family: 'comic sans ms', sans-serif; font-size: 12pt;"></span></p>
<p style="font-size: 16px; line-height: 26px; text-align: left; text-indent: 24pt;"><span style="font-family: 'comic sans ms', sans-serif; font-size: 12pt;">802.11s RMAODV路由協議使用了三種路由訊息封包，分別為路徑要求（Path Request，簡稱PREQ）、路徑回覆（Path Reply，簡稱PREP）、路徑錯誤（Path Error，簡稱PERR）[10][12]。</span></p>
<p style="font-size: 16px; line-height: 26px; text-align: left; text-indent: 24pt;"><span style="font-family: 'comic sans ms', sans-serif; font-size: 12pt;"></span></p>
<p style="font-size: 16px; line-height: 26px; text-align: left; text-indent: 24pt;"><span style="font-family: 'comic sans ms', sans-serif; font-size: 12pt;">其路由建立的步驟如下圖：</span></p>
<p style="text-indent: 24pt; line-height: 150%; text-align: left;"><span style="font-family: 'comic sans ms', sans-serif; font-size: 12pt;"></span></p>
<p style="text-indent: 24pt; line-height: 150%; text-align: left;"><span style="font-family: 'comic sans ms', sans-serif; font-size: 12pt;">&nbsp;<img decoding="async" class=" size-full wp-image-27" src="http://codeant.cc/wp-content/uploads/2013/07/images_phocagallery_Network_80211s-rmaodv-step.jpg" alt="80211s-rmaodv-step" width="549" height="395" style="display: block; margin-left: auto; margin-right: auto;" srcset="http://codeant.cc/wp-content/uploads/2013/07/images_phocagallery_Network_80211s-rmaodv-step.jpg 549w, http://codeant.cc/wp-content/uploads/2013/07/images_phocagallery_Network_80211s-rmaodv-step-300x216.jpg 300w" sizes="(max-width: 549px) 100vw, 549px" /></span></p>
<p style="font-size: 16px; line-height: 26px; text-align: left; text-indent: 24pt;"><span style="font-family: 'comic sans ms', sans-serif; font-size: 12pt;"></span></p>
<p style="font-size: 16px; line-height: 26px; text-align: left; text-indent: 24pt;"><span style="font-family: 'comic sans ms', sans-serif; font-size: 12pt;">1. &nbsp; &nbsp;當發送端（Source）需要傳送資料時，以廣播的方式送出PREQ封包。</span><span style="font-family: 'comic sans ms', sans-serif; font-size: 12pt;"></span></p>
<p style="font-size: 16px; line-height: 26px; text-align: left; text-indent: 24pt;"><span style="font-family: 'comic sans ms', sans-serif; font-size: 12pt;">2.<span style="line-height: normal;">&nbsp; &nbsp;&nbsp;</span>鄰近節點收到發送端的PREQ封包後，進行再廣播（Re-Broadcast），藉此傳遞PREQ封包到達目的端（Destination）。</span><span style="font-family: 'comic sans ms', sans-serif; font-size: 12pt;"></span></p>
<p style="font-size: 16px; line-height: 26px; text-align: left; text-indent: 24pt;"><span style="font-family: 'comic sans ms', sans-serif; font-size: 12pt;">3.<span style="line-height: normal;">&nbsp; &nbsp;&nbsp;</span>目的端收到PREQ封包後，以單點直播（Unicast）的方式回覆PREP封包。</span><span style="font-family: 'comic sans ms', sans-serif; font-size: 12pt;"></span></p>
<p style="font-size: 16px; line-height: 26px; text-align: left; text-indent: 24pt;"><span style="font-family: 'comic sans ms', sans-serif; font-size: 12pt;">4.<span style="line-height: normal;">&nbsp; &nbsp;&nbsp;</span>PREP封包傳遞過程中，每一個節點都會選擇最佳的下一跳節點進行轉發，而收到PREP封包的節點會選擇將PREP封包傳送過來的節點作為到達目的端的路徑。</span></p>
<p style="font-size: 16px; line-height: 26px; text-align: left; text-indent: 24pt;"><span style="font-family: 'comic sans ms', sans-serif; font-size: 12pt;">5.<span style="line-height: normal;">&nbsp; &nbsp;&nbsp;</span>當發送端收到PREP封包後，路由資訊即建立完成，這樣由目的端往來源端方向確認路由的方式，也稱為反向路由（Reverse routing）。</span><span style="font-family: 'comic sans ms', sans-serif; font-size: 12pt;"></span></p>
<p style="font-size: 16px; line-height: 26px; text-align: left; text-indent: 24pt;"><span style="font-family: 'comic sans ms', sans-serif; font-size: 12pt;">6.<span style="line-height: normal;">&nbsp; &nbsp;&nbsp;</span>當發送端發現路由出現錯誤時，會以廣播的方式送出PERR封包，鄰近節點進行再廣播，通知各節點刪除現有的路由資訊，並回到第1步驟重新建立路由。</span><span style="font-family: 'comic sans ms', sans-serif; font-size: 12pt;"></span></p>
<p style="font-size: 16px; line-height: 26px; text-align: left; text-indent: 24pt;"><span style="font-family: 'comic sans ms', sans-serif; font-size: 12pt;">&nbsp; &nbsp; &nbsp; &nbsp;</span></p>
<p style="font-size: 16px; line-height: 26px; text-align: left; text-indent: 24pt;"><span style="font-family: 'comic sans ms', sans-serif; font-size: 12pt;">&nbsp; &nbsp; &nbsp; &nbsp;802.11s RMAODV透過下面算式進行路徑選擇，其中Ca為連線品質，O為額外時間，Bt為訊框長度，r為傳輸速率（transmission rate），ef為訊框（frame）傳輸的錯誤率。Ca值越小代表路徑品質越好，算式中r與ef，反應了節點間的無線訊號品質，當訊號品質下降，會導致ef值上升及r值下降。</span></p>
<p style="margin-left: 24.1pt; text-indent: -24.1pt; line-height: 150%; text-align: left;"><span style="font-family: 'comic sans ms', sans-serif;"><span style="font-size: 12pt;"></span></span></p>
<p style="margin-left: 24.1pt; text-indent: -24.1pt; line-height: 150%; text-align: center;"><span style="font-family: 標楷體;"><span style="font-size: 12pt; font-family: 標楷體;"><img decoding="async" class=" size-full wp-image-28" src="http://codeant.cc/wp-content/uploads/2013/07/images_phocagallery_Network_80211s-cost.jpg" alt="80211s-cost" width="140" height="63" /></span></span></p>
<p style="text-align: justify; text-indent: 24pt; line-height: 150%;"><span style="font-family: 標楷體;"></span></p>
<p style="text-align: justify; text-indent: 24pt; line-height: 150%;"><span style="font-size: 12pt; font-family: 標楷體;"></span></p>
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