UDP协议
<span lang="EN-US"></span><span style="font-family:宋体;mso-ascii-font-family:Calibri;mso-ascii-theme-font:minor-latin;mso-fareast-font-family:宋体;mso-fareast-theme-font:minor-fareast;
mso-hansi-font-family:Calibri;mso-hansi-theme-font:minor-latin"> </span><span lang="EN-US">UDP</span><span style="font-family:宋体;mso-ascii-font-family:Calibri;
mso-ascii-theme-font:minor-latin;mso-fareast-font-family:宋体;mso-fareast-theme-font:
minor-fareast;mso-hansi-font-family:Calibri;mso-hansi-theme-font:minor-latin">协议的全称是用户数据报，在网络中它与</span><span lang="EN-US">TCP</span><span style="font-family:宋体;mso-ascii-font-family:Calibri;
mso-ascii-theme-font:minor-latin;mso-fareast-font-family:宋体;mso-fareast-theme-font:
minor-fareast;mso-hansi-font-family:Calibri;mso-hansi-theme-font:minor-latin">协议一样用于处理数据包。在</span><span lang="EN-US">OSI</span><span style="font-family:宋体;mso-ascii-font-family:Calibri;
mso-ascii-theme-font:minor-latin;mso-fareast-font-family:宋体;mso-fareast-theme-font:
minor-fareast;mso-hansi-font-family:Calibri;mso-hansi-theme-font:minor-latin">模型中，在第四层</span><span lang="EN-US">——</span><span style="font-family:宋体;mso-ascii-font-family:Calibri;
mso-ascii-theme-font:minor-latin;mso-fareast-font-family:宋体;mso-fareast-theme-font:
minor-fareast;mso-hansi-font-family:Calibri;mso-hansi-theme-font:minor-latin">传输层，处于</span><span lang="EN-US">IP</span><span style="font-family:宋体;mso-ascii-font-family:Calibri;
mso-ascii-theme-font:minor-latin;mso-fareast-font-family:宋体;mso-fareast-theme-font:
minor-fareast;mso-hansi-font-family:Calibri;mso-hansi-theme-font:minor-latin">协议的上一层。</span><span lang="EN-US">UDP</span><span style="font-family:宋体;mso-ascii-font-family:Calibri;
mso-ascii-theme-font:minor-latin;mso-fareast-font-family:宋体;mso-fareast-theme-font:
minor-fareast;mso-hansi-font-family:Calibri;mso-hansi-theme-font:minor-latin">有不提供数据报分组、组装和不能对数据包的排序的缺点，也就是说，当报文发送之后，是无法得知其是否安全完整到达的。</span><span style="font-size:12.0pt;font-family:宋体;mso-bidi-font-family:宋体;
mso-font-kerning:0pt" lang="EN-US"></span>
<p class="MsoNormal" style="text-indent:21.0pt"><span style="font-size:12.0pt;font-family:宋体;mso-bidi-font-family:宋体;mso-font-kerning:
0pt" lang="EN-US">UDP</span><span style="font-size:12.0pt;font-family:宋体;mso-bidi-font-family:
宋体;mso-font-kerning:0pt">用来支持那些需要在计算机之间传输数据的网络应用。包括</span><span style="font-family:宋体;mso-ascii-font-family:Calibri;mso-ascii-theme-font:minor-latin;
mso-fareast-font-family:宋体;mso-fareast-theme-font:minor-fareast;mso-hansi-font-family:
Calibri;mso-hansi-theme-font:minor-latin">网络视频会以系</span><span style="font-size:
12.0pt;font-family:宋体;mso-bidi-font-family:宋体;mso-font-kerning:0pt">统在内的众多的客户<span lang="EN-US">/</span>服务器模式的网络应用都需要使用<span lang="EN-US">UDP</span>协议。<span lang="EN-US">UDP</span>协议从问世至今已经被使用了很多年，虽然其最初的光彩已经被一些类似协议所掩盖，但是即使是在今天，<span lang="EN-US">UDP</span>仍然不失为一项非常实用和可行的网络传输层协议。<span lang="EN-US"><span style="mso-tab-count:1"> </span></span></span></p>
<p class="MsoNormal" style="text-indent:21.0pt"><span style="font-size:12.0pt;font-family:宋体;mso-bidi-font-family:宋体;mso-font-kerning:
0pt" lang="EN-US">UDP</span><span style="font-size:12.0pt;font-family:宋体;mso-bidi-font-family:
宋体;mso-font-kerning:0pt">协议的主要作用是将</span><span style="font-family:宋体;
mso-ascii-font-family:Calibri;mso-ascii-theme-font:minor-latin;mso-fareast-font-family:
宋体;mso-fareast-theme-font:minor-fareast;mso-hansi-font-family:Calibri;
mso-hansi-theme-font:minor-latin">网络数据</span><span style="font-size:12.0pt;
font-family:宋体;mso-bidi-font-family:宋体;mso-font-kerning:0pt">流量压缩成数据包的形式。一个典型的数据包就是一个二进制数据的传输单位。每一个数据包的前<span lang="EN-US">8</span>个字节用来包含报头信息，剩余字节则用来包含具体的传输数据。<span lang="EN-US"></span></span></p>
<p class="MsoNormal" style="text-indent:21.0pt"><span style="font-size:12.0pt;font-family:宋体;mso-bidi-font-family:宋体;mso-font-kerning:
0pt" lang="EN-US">UDP</span><span style="font-size:12.0pt;font-family:宋体;mso-bidi-font-family:
宋体;mso-font-kerning:0pt">的特性：它不属于连接型协议，因而具有资源消耗小，处理速度快的优点，所以通常音频、视频和普通数据在传送时使用<span lang="EN-US">UDP</span>较多，因为它们即使偶尔丢失一两个数据包，也不会对接 收结果产生太大影响。比如我们聊天用的<span lang="EN-US">ICQ</span>和<span lang="EN-US">QQ</span>就是使用的<span lang="EN-US">UDP</span>协议。<span lang="EN-US"></span></span></p>
<p class="MsoNormal" style="text-align:left;text-indent:21.0pt;
mso-pagination:widow-orphan" align="left"><span style="font-size:12.0pt;
font-family:宋体;mso-bidi-font-family:宋体;mso-font-kerning:0pt" lang="EN-US">UDP</span><span style="font-size:12.0pt;font-family:宋体;mso-bidi-font-family:宋体;mso-font-kerning:
0pt">报头由<span lang="EN-US">4</span>个域组成，其中每个域各占用<span lang="EN-US">2</span>个字节，具体如下：<span lang="EN-US"></span></span></p><p class="MsoNormal" style="text-align:left;mso-pagination:widow-orphan" align="left"><span style="font-size:12.0pt;font-family:宋体;mso-bidi-font-family:宋体;mso-font-kerning:
0pt">源端口号 目标端口号 数据报长度 校验值<span lang="EN-US"></span></span></p>
<p class="MsoNormal" style="text-align:left;mso-pagination:widow-orphan" align="left"><span style="font-size:12.0pt;font-family:宋体;mso-bidi-font-family:宋体;
mso-font-kerning:0pt" lang="EN-US"> </span></p>
<p class="MsoNormal" style="text-align:left;text-indent:21.0pt;
mso-pagination:widow-orphan" align="left"><span style="font-size:12.0pt;
font-family:宋体;mso-bidi-font-family:宋体;mso-font-kerning:0pt" lang="EN-US">UDP</span><span style="font-size:12.0pt;font-family:宋体;mso-bidi-font-family:宋体;mso-font-kerning:
0pt">协议使用端口号为不同的应用保留其各自的数据传输通道。<span lang="EN-US">UDP</span>和</span><span lang="EN-US">TCP</span><span style="font-family:宋体;mso-ascii-font-family:Calibri;
mso-ascii-theme-font:minor-latin;mso-fareast-font-family:宋体;mso-fareast-theme-font:
minor-fareast;mso-hansi-font-family:Calibri;mso-hansi-theme-font:minor-latin">协议</span><span style="font-size:12.0pt;font-family:宋体;mso-bidi-font-family:宋体;mso-font-kerning:
0pt">正是采用这一机制实现对同一时刻内多项应用同时发送和接收数据的支持。数据发送一方（可以是客户端或服务器端）将<span lang="EN-US">UDP</span>数据报通过源端口发送出去，而数据接收一方则通过目标端口接收数据。有的网络应用只能使用预先为其预留或注册的静态端口；而另外一些网络应用则可以使用未被注册的动态端口。因为<span lang="EN-US">UDP</span>报头使用两个字节存放端口号，所以端口号的有效范围是从<span lang="EN-US">0</span>到<span lang="EN-US">65535</span>。一般来说，大于<span lang="EN-US">49151</span>的端口号都代表动态端口。 <span lang="EN-US"></span></span></p>
<p class="MsoNormal" style="text-align:left;mso-pagination:widow-orphan" align="left"><span style="font-size:12.0pt;font-family:宋体;mso-bidi-font-family:宋体;mso-font-kerning:
0pt"> 数据报的长度是指包括报头和数据部分在内的总字节数。因为报头的长度是固定的，所以该域主要被 用来计算可变长度的数据部分（又称为数据负载）。数据报的最大长度根据操作环境的不同而各异。从理论上说，包含报头在内的数据报的最大长度为<span lang="EN-US">65535</span>字 节。不过，一些实际应用往往会限制数据报的大小，有时会降低到<span lang="EN-US">8192</span>字节。
<span lang="EN-US"></span></span></p>
<p class="MsoNormal" style="text-align:left;text-indent:24.0pt;
mso-pagination:widow-orphan" align="left"><span style="font-size:12.0pt;
font-family:宋体;mso-bidi-font-family:宋体;mso-font-kerning:0pt" lang="EN-US">UDP</span><span style="font-size:12.0pt;font-family:宋体;mso-bidi-font-family:宋体;mso-font-kerning:
0pt">协议使用报头中的校验值来保证数据的安全。校验值首先在数据发送方通过特殊的算法计算得 出，在传递到接收方之后，还需要再重新计算。如果某个数据报在传输过程中被第三方篡改或者由于线路噪音等原因受到损坏，发送和接收方的校验计算值将不会相符，由此<span lang="EN-US">UDP</span>协议可以检测是否出错。这与<span lang="EN-US">TCP</span>协议是不同的，后者要求必须具有校验值。<span lang="EN-US"></span></span></p>
<p class="MsoNormal" style="text-align:left;text-indent:24.0pt;
mso-pagination:widow-orphan" align="left"><span style="font-size:12.0pt;font-family:宋体;
mso-bidi-font-family:宋体;mso-font-kerning:0pt">许多链路层协议都提供错误检查，包括流行的以太网协议，也许想知道为什么<span lang="EN-US">UDP</span>也要提供检查，其原因是链路层以下的协议在源端和终端间的某些通道可能不提供错误检测。虽然<span lang="EN-US">UDP</span>提供有错误检测，但检测到错误时，<span lang="EN-US">UDP</span>不做错误校正，只是简单地把损坏的消息段扔掉，或者给应用程序提供警告信息。<span lang="EN-US"></span></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:
auto;text-align:left;mso-pagination:widow-orphan;mso-outline-level:2" align="left"><b><span style="font-size:18.0pt;font-family:宋体;mso-bidi-font-family:宋体;
mso-font-kerning:0pt" lang="EN-US">UDP</span></b><b><span style="font-size:18.0pt;
font-family:宋体;mso-bidi-font-family:宋体;mso-font-kerning:0pt">协议的几个特性<span lang="EN-US"></span></span></b></p>
<p class="MsoNormal" style="text-align:left;mso-pagination:widow-orphan" align="left"><span style="font-size:12.0pt;font-family:宋体;mso-bidi-font-family:宋体;mso-font-kerning:
0pt"> （<span lang="EN-US">1</span>）<span lang="EN-US"> UDP</span>是一个无连接协议，传输数据之前源端和终端不建立连接，当<span lang="EN-US"></span></span><span style="font-size:12.0pt;font-family:宋体;mso-bidi-font-family:宋体;mso-font-kerning:
0pt" lang="EN-US">UDP</span><span style="font-size:12.0pt;font-family:宋体;mso-bidi-font-family:
宋体;mso-font-kerning:0pt">它想传送时就简单地去抓取来自应用程序的数据，并尽可能快地把它扔到网络上。在发送端，<span lang="EN-US">UDP</span>传送数据的速度仅仅是受应用程序生成数据的速度、计算机的能力和传输带宽的限制；在接收端，<span lang="EN-US">UDP</span>把每个消息段放在队列中，应用程序每次从队列中读一个消息段。<span lang="EN-US"></span></span>
</p><p class="MsoNormal" style="text-align:left;text-indent:21.0pt;
mso-pagination:widow-orphan" align="left"><span style="font-size:12.0pt;font-family:宋体;
mso-bidi-font-family:宋体;mso-font-kerning:0pt">（<span lang="EN-US">2</span>） 由于传输数据不建立连接，因此也就不需要维护连接状态，包括收发状态等，因此一台服务机可同时向多个客户机传输相同的消息。
<span lang="EN-US"></span></span></p>
<p class="MsoNormal" style="text-align:left;mso-pagination:widow-orphan" align="left"><span style="font-size:12.0pt;font-family:宋体;mso-bidi-font-family:宋体;mso-font-kerning:
0pt"> （<span lang="EN-US">3</span>）<span lang="EN-US"> UDP</span>信息包的标题很短，只有<span lang="EN-US">8</span>个字节，相对于<span lang="EN-US">TCP</span>的<span lang="EN-US">20</span>个字节信息包的额外开销很小。
<span lang="EN-US"></span></span></p>
<p class="MsoNormal" style="text-align:left;mso-pagination:widow-orphan" align="left"><span style="font-size:12.0pt;font-family:宋体;mso-bidi-font-family:宋体;mso-font-kerning:
0pt"> （<span lang="EN-US">4</span>） 吞吐量不受拥挤控制算法的调节，只受</span><span style="font-family:宋体;mso-ascii-font-family:Calibri;mso-ascii-theme-font:minor-latin;
mso-fareast-font-family:宋体;mso-fareast-theme-font:minor-fareast;mso-hansi-font-family:
Calibri;mso-hansi-theme-font:minor-latin">应用程序生产</span><span style="font-size:
12.0pt;font-family:宋体;mso-bidi-font-family:宋体;mso-font-kerning:0pt">数据的速率、传输带宽、源端和终端主机性能的限制。
<span lang="EN-US"></span></span></p>
<p class="MsoNormal" style="text-indent:21.0pt"><span style="font-size:12.0pt;
font-family:宋体;mso-bidi-font-family:宋体;mso-font-kerning:0pt">（<span lang="EN-US">5</span>）<span lang="EN-US">UDP</span>使用尽最大努力交付<b>，</b>即不保证可靠交付，因此主机不需要维持复杂的链接状态表（这里面有许多参数）。<span lang="EN-US"></span></span></p>
<p class="MsoNormal" style="text-align:left;text-indent:21.0pt;
mso-pagination:widow-orphan" align="left"><span style="font-size:12.0pt;font-family:宋体;
mso-bidi-font-family:宋体;mso-font-kerning:0pt">（<span lang="EN-US">6</span>）<span lang="EN-US">UDP</span>是面向报文的。发送方的<span lang="EN-US">UDP</span>对应用程序交下来的报文，在添加首部后就向下交付给<span lang="EN-US">IP</span>层。既不拆分，也不合并，而是保留这些报文的边界，因此，应用程序需要选择合适的报文大小。 <span lang="EN-US"></span></span></p>
<p class="MsoNormal" style="text-align:left;mso-pagination:widow-orphan" align="left"><span style="font-size:12.0pt;font-family:宋体;mso-bidi-font-family:宋体;mso-font-kerning:
0pt"> 虽然<span lang="EN-US">UDP</span>是一个不可靠的协议，但它是分发信息的一个理想协议。例如，在屏幕上报告股票市场、在屏幕上显示航空信息等等。<span lang="EN-US">UDP</span>也用在路由信息协议<span lang="EN-US">RIP</span>（<span lang="EN-US">Routing
Information Protocol</span>）中修改路由表。在这些应用场合下，如果有一个消息丢失，在几秒之后另一个新的消息就会替换它。<span lang="EN-US">UDP</span>广泛用在多媒体应用中，例如，<span lang="EN-US">Progressive Networks</span>公司开发的<span lang="EN-US">RealAudio</span>软件，它是在</span><span style="font-family:宋体;mso-ascii-font-family:
Calibri;mso-ascii-theme-font:minor-latin;mso-fareast-font-family:宋体;mso-fareast-theme-font:
minor-fareast;mso-hansi-font-family:Calibri;mso-hansi-theme-font:minor-latin">因特网上</span><span style="font-size:12.0pt;font-family:宋体;mso-bidi-font-family:宋体;mso-font-kerning:
0pt">把预先录制的或者现场音乐实时传送给客户机的一种软件，该软件使用的<span lang="EN-US">RealAudio audio-on-demand
protocol</span>协议就是运行在<span lang="EN-US">UDP</span>之上的协议，大多数因特网电话软件产品也都运行在<span lang="EN-US">UDP</span>之上。<span lang="EN-US"></span></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:
auto;text-align:left;mso-pagination:widow-orphan;mso-outline-level:2" align="left"><b><span style="font-size:18.0pt;font-family:宋体;mso-bidi-font-family:宋体;
mso-font-kerning:0pt" lang="EN-US">UDP vs TCP</span></b></p>
<p class="MsoNormal" style="text-indent:21.0pt"><span style="font-size:12.0pt;font-family:宋体;mso-bidi-font-family:宋体;mso-font-kerning:
0pt" lang="EN-US">UDP</span><span style="font-size:12.0pt;font-family:宋体;mso-bidi-font-family:
宋体;mso-font-kerning:0pt">和<span lang="EN-US">TCP</span>协议的主要区别是两者在如何实现信息的可靠传递方面不同。<span lang="EN-US"></span></span></p>
<p class="MsoNormal" style="text-indent:21.0pt"><span style="font-size:12.0pt;font-family:宋体;mso-bidi-font-family:宋体;mso-font-kerning:
0pt" lang="EN-US">TCP </span><span style="font-size:12.0pt;font-family:宋体;mso-bidi-font-family:
宋体;mso-font-kerning:0pt">协议中包含了专门的传递保证机制，当数据接收方收到发送方传来的信息时，会自动向发送方发出确认消息；发送方只有在接收到该确认消息之后才继续传送其它信息，否则将一直等待直到收到确认信息为止。
<span lang="EN-US"></span></span></p>
<p class="MsoNormal" style="text-indent:21.0pt"><span style="font-size:12.0pt;
font-family:宋体;mso-bidi-font-family:宋体;mso-font-kerning:0pt">与<span lang="EN-US">TCP</span>不同，<span lang="EN-US">UDP</span>协议并不提供数据传送的保证机制。如果在从发送方到接收方的传递过程中出现数据报的丢失，协议本身并不能做出任何检测或提示。因此，
通常人们把<span lang="EN-US">UDP</span>协议称为<b>不可靠的传输协议</b>。<span lang="EN-US"></span></span></p>
<p class="MsoNormal" style="text-align:left;text-indent:21.0pt;
mso-pagination:widow-orphan" align="left"><span style="font-size:12.0pt;font-family:宋体;
mso-bidi-font-family:宋体;mso-font-kerning:0pt">相对于<span lang="EN-US">TCP</span>协议，<span lang="EN-US">UDP</span>协议的另外一个不同之处在于如何接收突发性的多个数据报。不同于<span lang="EN-US">TCP</span>，<span lang="EN-US">UDP</span>并不能确保数据的发送和接收顺序。例如，一个位于客户端的应用程序向服务器发出了以下<span lang="EN-US">4</span>个数据报
<span lang="EN-US"></span></span></p>
<p class="MsoNormal" style="text-align:left;mso-pagination:widow-orphan" align="left"><span style="font-size:12.0pt;font-family:宋体;mso-bidi-font-family:宋体;mso-font-kerning:
0pt"> <span lang="EN-US">D1 </span></span></p>
<p class="MsoNormal" style="text-align:left;mso-pagination:widow-orphan" align="left"><span style="font-size:12.0pt;font-family:宋体;mso-bidi-font-family:宋体;mso-font-kerning:
0pt"> <span lang="EN-US">D22 </span></span></p>
<p class="MsoNormal" style="text-align:left;mso-pagination:widow-orphan" align="left"><span style="font-size:12.0pt;font-family:宋体;mso-bidi-font-family:宋体;mso-font-kerning:
0pt"> <span lang="EN-US">D333 </span></span></p>
<p class="MsoNormal" style="text-align:left;mso-pagination:widow-orphan" align="left"><span style="font-size:12.0pt;font-family:宋体;mso-bidi-font-family:宋体;mso-font-kerning:
0pt"> <span lang="EN-US">D4444 </span></span></p>
<p class="MsoNormal" style="text-align:left;mso-pagination:widow-orphan" align="left"><span style="font-size:12.0pt;font-family:宋体;mso-bidi-font-family:宋体;mso-font-kerning:
0pt"> 但是<span lang="EN-US">UDP</span>有可能按照以下顺序将所接收的数据提交到服务端的应用： <span lang="EN-US"></span></span></p>
<p class="MsoNormal" style="text-align:left;mso-pagination:widow-orphan" align="left"><span style="font-size:12.0pt;font-family:宋体;mso-bidi-font-family:宋体;mso-font-kerning:
0pt"> <span lang="EN-US">D333 </span></span></p>
<p class="MsoNormal" style="text-align:left;mso-pagination:widow-orphan" align="left"><span style="font-size:12.0pt;font-family:宋体;mso-bidi-font-family:宋体;mso-font-kerning:
0pt"> <span lang="EN-US">D1 </span></span></p>
<p class="MsoNormal" style="text-align:left;mso-pagination:widow-orphan" align="left"><span style="font-size:12.0pt;font-family:宋体;mso-bidi-font-family:宋体;mso-font-kerning:
0pt"> <span lang="EN-US">D4444 </span></span></p>
<p class="MsoNormal" style="text-align:left;mso-pagination:widow-orphan" align="left"><span style="font-size:12.0pt;font-family:宋体;mso-bidi-font-family:宋体;mso-font-kerning:
0pt"> <span lang="EN-US">D22 </span></span></p>
<p class="MsoNormal" style="text-indent:21.0pt"><span style="font-size:12.0pt;
font-family:宋体;mso-bidi-font-family:宋体;mso-font-kerning:0pt">事实上，<span lang="EN-US">UDP</span>协议的这种乱序性基本上很少出现，通常只会在网络非常拥挤的情况下才有可能发生。<span lang="EN-US"></span></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:
auto;text-align:left;mso-pagination:widow-orphan;mso-outline-level:2" align="left"><b><span style="font-size:18.0pt;font-family:宋体;mso-bidi-font-family:宋体;
mso-font-kerning:0pt" lang="EN-US">UDP</span></b><b><span style="font-size:18.0pt;
font-family:宋体;mso-bidi-font-family:宋体;mso-font-kerning:0pt">协议的应用<span lang="EN-US"></span></span></b></p>
<p class="MsoNormal" style="text-align:left;mso-pagination:widow-orphan" align="left"><span style="font-size:12.0pt;font-family:宋体;mso-bidi-font-family:宋体;mso-font-kerning:
0pt"> 既然<span lang="EN-US">UDP</span>是一种不可靠的</span><span style="font-family:
宋体;mso-ascii-font-family:Calibri;mso-ascii-theme-font:minor-latin;mso-fareast-font-family:
宋体;mso-fareast-theme-font:minor-fareast;mso-hansi-font-family:Calibri;
mso-hansi-theme-font:minor-latin">网络协议，</span><span style="font-size:12.0pt;
font-family:宋体;mso-bidi-font-family:宋体;mso-font-kerning:0pt">那么还有什么使用价值或必要呢？其实不然，在有些情况下<span lang="EN-US">UDP</span>协议可能会变得非常有用。因为<span lang="EN-US">UDP</span>具有<span lang="EN-US">TCP</span>所望尘莫及的速度优势。虽然<span lang="EN-US">TCP</span>协议中植入了各种安全保障功能，但是在实际执行的过程中会占用大量的</span><span style="font-family:宋体;mso-ascii-font-family:Calibri;mso-ascii-theme-font:minor-latin;
mso-fareast-font-family:宋体;mso-fareast-theme-font:minor-fareast;mso-hansi-font-family:
Calibri;mso-hansi-theme-font:minor-latin">系统开销，</span><span style="font-size:
12.0pt;font-family:宋体;mso-bidi-font-family:宋体;mso-font-kerning:0pt">无疑使速度受到严重的影响。反观<span lang="EN-US">UDP</span>由于排除了信息可靠传递机制，将安全和排序等功能移交给上层应用来完成，极大降低了执行时间，使速度得到了保证。 <span lang="EN-US"></span></span></p>
<p class="MsoNormal" style="text-align:left;mso-pagination:widow-orphan" align="left"><span style="font-size:12.0pt;font-family:宋体;mso-bidi-font-family:宋体;mso-font-kerning:
0pt"> 关于<span lang="EN-US">UDP</span>协议的最早规范是<span lang="EN-US">RFC768</span>，<span lang="EN-US">1980</span>年发布。尽管时间已经很长，但是<span lang="EN-US">UDP</span>协议仍然继续在主流应用中发挥着作用。包括视频</span><span style="font-family:宋体;mso-ascii-font-family:Calibri;mso-ascii-theme-font:minor-latin;
mso-fareast-font-family:宋体;mso-fareast-theme-font:minor-fareast;mso-hansi-font-family:
Calibri;mso-hansi-theme-font:minor-latin">电话会议系统在</span><span style="font-size:
12.0pt;font-family:宋体;mso-bidi-font-family:宋体;mso-font-kerning:0pt">内的许多应用都证明了<span lang="EN-US">UDP</span>协议的存在价值。因为相对于可靠性来说，这些应用更加注重实际性能，所以为了获得更好的使用效果（例如，更高的画面帧刷新速
率）往往可以牺牲一定的可靠性（例如，画面质量）。这就是<span lang="EN-US">UDP</span>和<span lang="EN-US">TCP</span>两种协议的权衡之处。根据不同的环境和特点，两种传输协议都将在今后的网络世界中
发挥更加重要的作用。<span lang="EN-US"></span></span></p>
<p class="MsoNormal" style="text-indent:21.0pt"><span lang="EN-US"> </span></p>
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