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<meta name="description" content="What is Internet &amp; Protocal? 这节课上完需要能回答的问题： What is Internet? What is Protocol?(这个人说，如果你想描述一个东西，就描述这个东西的各个部分。) Internet edge: 就是说那些终端？用网络的东西，手机电脑什么的 设备。也叫 hosts (end systems) 有一个特别好玩的项目">
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<meta property="og:description" content="What is Internet &amp; Protocal? 这节课上完需要能回答的问题： What is Internet? What is Protocol?(这个人说，如果你想描述一个东西，就描述这个东西的各个部分。) Internet edge: 就是说那些终端？用网络的东西，手机电脑什么的 设备。也叫 hosts (end systems) 有一个特别好玩的项目">
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<time title="创建时间：2024-09-09 00:13:20 / 修改时间：01:38:50" itemprop="dateCreated datePublished" datetime="2024-09-09T00:13:20+08:00">2024-09-09</time>
<time title="创建时间：2024-09-09 00:13:20 / 修改时间：01:51:47" itemprop="dateCreated datePublished" datetime="2024-09-09T00:13:20+08:00">2024-09-09</time>
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<h1 id="What-is-Internet-amp-Protocal"><a href="#What-is-Internet-amp-Protocal" class="headerlink" title="What is Internet &amp; Protocal?"></a>What is Internet &amp; Protocal?</h1><blockquote>
<p>这节课上完需要能回答的问题：<br> What is Internet?<br> What is Protocol?<br>(这个人说，如果你想描述一个东西，就描述这个东西的各个部分。)</p>
</blockquote>
<!---more--->
<span id="more"></span>

<ul>
<li>Internet edge: <ul>
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<span class="post-meta-item-text">发表于</span>


<time title="创建时间：2024-09-09 00:13:20 / 修改时间：01:38:50" itemprop="dateCreated datePublished" datetime="2024-09-09T00:13:20+08:00">2024-09-09</time>
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<h1 id="What-is-Internet-amp-Protocal"><a href="#What-is-Internet-amp-Protocal" class="headerlink" title="What is Internet &amp; Protocal?"></a>What is Internet &amp; Protocal?</h1><blockquote>
<p>这节课上完需要能回答的问题：<br> What is Internet?<br> What is Protocol?<br>(这个人说，如果你想描述一个东西，就描述这个东西的各个部分。)</p>
</blockquote>
<!---more--->

<ul>
<li>Internet edge: <ul>
<li>就是说那些终端？用网络的东西，手机电脑什么的 <strong>设备</strong>。也叫 hosts (<strong>end systems</strong>)</li>
<li>有一个特别好玩的项目，就是烤面包机连上网络天气预报，就是说是什么天气就把面包烤黑出那个天气的符号。</li>
</ul>
</li>
<li>Packet Switches:<ul>
<li>routers 路由器, switches 交换器</li>
<li>chunks of data</li>
</ul>
</li>
<li>Communication links:<ul>
<li>fiber, copper, radio, statellite</li>
</ul>
</li>
<li>Networks:<ul>
<li>Connects of devices, routers, links</li>
</ul>
</li>
</ul>
<h2 id="Internet"><a href="#Internet" class="headerlink" title="Internet:"></a>Internet:</h2><ul>
<li>The Network of Networks</li>
<li>类比 邮政服务 postal service，是一系列网络应用的基石。</li>
</ul>
<h2 id="protocols"><a href="#protocols" class="headerlink" title="protocols:"></a>protocols:</h2><ul>
<li>协议，就是控制发送接收的信息要以什么形式体现什么的吧。</li>
<li>Internet standards<ul>
<li>RFC: Request for Comments</li>
<li>IETF: Internet Engineering Task Force</li>
</ul>
</li>
</ul>
<h1 id="The-network-edge"><a href="#The-network-edge" class="headerlink" title="The network edge"></a>The network edge</h1><blockquote>
<p>device, hosts:<br> clients and servers<br>access networks, physical media<br>network core</p>
</blockquote>
<ul>
<li>Q: How to connect end systems to edge router?<ol>
<li>residential access nets (住宅接入网)</li>
<li>institutional access networkds</li>
<li>mobile access networks</li>
</ol>
</li>
</ul>
<h2 id="Access-networks"><a href="#Access-networks" class="headerlink" title="Access networks:"></a>Access networks:</h2><h3 id="cable-based-access"><a href="#cable-based-access" class="headerlink" title="cable-based access"></a>cable-based access</h3><ul>
<li>有线访问，有线访问你想想就那么一条线，连着好多家，只是分开了而已，为什么能够每家都分得出来呢？<ul>
<li>每家和电台一样都有不同的频率，但是频率是有限的，所以你可能和你邻居是一样的频率。也就是：<ul>
<li>frequency division multiplexing 频率复用 (FDM)</li>
</ul>
</li>
</ul>
</li>
<li>有线网络 Asymmetric 什么意思？<ul>
<li>意思是不对称，有线网络访问通常上传速度慢，下载速度快，因为网络运行商默认我们是数据的接收者使用者，而不是发出者。</li>
</ul>
</li>
<li>ISP:<ul>
<li>互联网提供商 Internet Service Provider.</li>
</ul>
</li>
</ul>
<h3 id="digital-subscriber-line-DSL"><a href="#digital-subscriber-line-DSL" class="headerlink" title="digital subscriber line (DSL)"></a>digital subscriber line (DSL)</h3><ul>
<li>简单说就是用电话线带来不和邻居共享的网络。</li>
<li>也是 asymmetric, 但是挺慢的。</li>
<li>就是用之前电话线已经铺设好的线路了，不需要再重新设置线路，这个网络是接到本地电话交换机，通常就是一个街区有那么一个，然后再接电话线进你家。</li>
<li>哦哦，为什么叫做这个名字，因为 subscriber line 就是电话线的意思哈哈哈哈哈哈。</li>
</ul>
<h3 id="home-network"><a href="#home-network" class="headerlink" title="home network"></a>home network</h3><ul>
<li>家里有个 DSL&#x2F;cable modem 调制解调器，用来连进 DSL&#x2F;cable. </li>
<li>然后接进入 router, 然后分别连接有线设备或者无线设备。</li>
</ul>
<h3 id="Wireless-access-networks"><a href="#Wireless-access-networks" class="headerlink" title="Wireless access networks"></a>Wireless access networks</h3><h4 id="wireless-local-area-networks-WLANs"><a href="#wireless-local-area-networks-WLANs" class="headerlink" title="wireless local area networks (WLANs)"></a>wireless local area networks (WLANs)</h4><ul>
<li>就是wifi什么的。</li>
</ul>
<h4 id="wide-area-cellular-access-networks"><a href="#wide-area-cellular-access-networks" class="headerlink" title="wide-area cellular access networks"></a>wide-area cellular access networks</h4><ul>
<li>就是 4G, 5G 什么的。</li>
<li>cellular 在这里有移动电话的意思。</li>
</ul>
<h3 id="enterprise-networks"><a href="#enterprise-networks" class="headerlink" title="enterprise networks"></a>enterprise networks</h3><ol>
<li>就是企业用网络，和家用的区别就是会有多个 switches &amp; routers。</li>
<li>另一种就是 数据中心。</li>
</ol>
<h2 id="Links-physic-media"><a href="#Links-physic-media" class="headerlink" title="Links: physic media"></a>Links: physic media</h2><ul>
<li>bits: <ul>
<li>propagates (传输) between transmitter&#x2F;receiver pairs</li>
</ul>
</li>
<li>physical link:<ul>
<li>what lies between transmitter &amp; reciever</li>
</ul>
</li>
<li>guided media:<ul>
<li>signals propagate in solid media: copper, fiber, coax</li>
<li>e.g. <ul>
<li>twisted pair (TP)</li>
<li>两股扭在一起的线</li>
</ul>
</li>
</ul>
</li>
<li>unguided media:<ul>
<li>signals propagate freely, like radio.<ul>
<li>wifi, wide-area, bluetooth, 都算</li>
</ul>
</li>
</ul>
</li>
</ul>
<h1 id="Network-Core"><a href="#Network-Core" class="headerlink" title="Network Core"></a>Network Core</h1><blockquote>
<p>packet switching<br>circuit switching<br>structure of today’s internet</p>
</blockquote>
<ul>
<li>network core 简单来说就是相互连接的路由器 routers。</li>
<li>packet-switching:<ul>
<li>就是把整个数据打乱分成小包，然后把这些包发到不同的 router 上，然后慢慢转移到其他的 router 上，慢慢转到最终目的地。</li>
</ul>
</li>
</ul>
<h2 id="forwarding"><a href="#forwarding" class="headerlink" title="forwarding"></a>forwarding</h2><ul>
<li>sometimes also known as switching and routing.</li>
<li>就是说整个全世界的 routers 里面都有一个 local forwarding table, 然后每个包的 header 里面都有一个 destination address, 每个包经过这个 router 的时候就查看下这个 table，上面就写了你要去哪里就怎么走，往哪转。</li>
</ul>
<h2 id="routing"><a href="#routing" class="headerlink" title="routing"></a>routing</h2><ul>
<li>routing 干的事就更难一些，像导航一样去计算出应该往哪跳，</li>
</ul>
<h2 id="Transmission-of-the-packet-bits"><a href="#Transmission-of-the-packet-bits" class="headerlink" title="Transmission of the packet bits"></a>Transmission of the packet bits</h2><h3 id="Hosts-sends-packets-of-data"><a href="#Hosts-sends-packets-of-data" class="headerlink" title="Hosts: sends packets of data"></a>Hosts: sends packets of data</h3><ul>
<li>什么意思？就是说，你传输数据的时候是把整个数据拆分成一个个小块，然后通过 protocal 来每个小块加上 header 什么的，便于传输的一致性。</li>
<li>L: <ul>
<li>每个块的 bits 大小长度</li>
</ul>
</li>
<li>R: <ul>
<li>transmission rate, 每秒钟能传输多少 bits</li>
</ul>
</li>
<li>packet transmission delay:<ul>
<li>$\frac{L}{R}$</li>
</ul>
</li>
</ul>
<h3 id="store-and-forward"><a href="#store-and-forward" class="headerlink" title="store and forward:"></a>store and forward:</h3><ul>
<li>就是说，必须要每个小 packet 全部到了才能 forward，在没全传输完之前只能先 store。</li>
</ul>
<h3 id="packet-switching-queueing"><a href="#packet-switching-queueing" class="headerlink" title="packet-switching: queueing"></a>packet-switching: queueing</h3><ul>
<li>就是说在第一跳的数据很多，但是第二跳 R 很慢，要等，就要排队，就要 queue。<img src="https://raw.githubusercontent.com/GEORGE-Ta/G_image_host/main/202409081812287.png" alt="image.png"></li>
<li>! 噔噔噔 ！<ul>
<li>如果实在是太多东西排队积压，一个 router 里的 memory 放满了，那剩下挤不进来的东西就会被丢弃。</li>
</ul>
</li>
</ul>
<h2 id="circuit-switching"><a href="#circuit-switching" class="headerlink" title="circuit-switching"></a>circuit-switching</h2><ul>
<li>和 packet-switching 是同一 level 的，是 switching 的不同方法。</li>
<li>call 的概念替代 packet 的概念。（但实际上，circuit-switching 是比 packet-switching 更早的概念，是用来给电话信号用的。</li>
<li>没有 delay，没有 lost，就是一个 call 就要从头走到尾。</li>
<li>但是：<ul>
<li>因为他必须要每次都从头走到尾，而且有固定的线路，如果这一个 call 其实跑不满这个线路的话，其实很浪费，空余的地方其他的也不能用，就只能等，所以 circuit-switching 效率很低。</li>
</ul>
</li>
</ul>
<h3 id="Frequency-Division-Multiplexing"><a href="#Frequency-Division-Multiplexing" class="headerlink" title="Frequency Division Multiplexing"></a>Frequency Division Multiplexing</h3><blockquote>
<p>FDM</p>
<ul>
<li>就是同一频率的分一组<img src="https://raw.githubusercontent.com/GEORGE-Ta/G_image_host/main/FDM.png" alt="image.png"></li>
</ul>
</blockquote>
<ul>
<li>FDM 适合模拟信号的传播，因为不能断是吧，而且是可以同一时间传播不同的频率的。</li>
</ul>
<h3 id="Time-Division-Multiplexing"><a href="#Time-Division-Multiplexing" class="headerlink" title="Time Division Multiplexing"></a>Time Division Multiplexing</h3><blockquote>
<p>TDM</p>
</blockquote>
<ul>
<li>就是同一个时间的分同一组<img src="https://raw.githubusercontent.com/GEORGE-Ta/G_image_host/main/TDM.png" alt="image.png"></li>
<li>TDM 适合数字信号传播，因为数字信号也是一段一段的对吧，可以分割，所以适合数据传输。</li>
</ul>
<h3 id="Network-of-Networks"><a href="#Network-of-Networks" class="headerlink" title="Network of Networks"></a>Network of Networks</h3><ul>
<li><img src="https://raw.githubusercontent.com/GEORGE-Ta/G_image_host/main/network.png" alt="image.png"></li>
<li>这里的 IXP 是 internet exchange point。<img src="https://raw.githubusercontent.com/GEORGE-Ta/G_image_host/main/202409081907849.png" alt="image.png"></li>
</ul>

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