多路复用技术能够提高传输系统利用率。常用的多路复用技术有(34)。将一条物理信道分成若干时间片，轮换地给多个信号使用，实现一条物理信道传输多个数字信号，这是(35)。将物理信道的总频带宽分割成若干个子信道，每个信道传输一路信号，这是(36)。在光纤中采用的多路复用技术是(37)，多路复用技术一般不用于(38)中。

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VRML is a(71)for 3D multimedia and shared virtual worlds on the WWW. In comparison to HTML, VRML adds the next level of interaction, structured graphics, and extra(72)(z and time)to the presentation of documents. The applications of VRML are(73), ranging from simple business graphics to entertaining WWW page graphics, manufacturing, scientific, entertainment, and educational applications, and 3D shared virtual worlds and communities.

 X3D is the name under which the development of VRML is continued. X3D is based on XML and is backwards(74)with VRML. Furthermore, it is componentized, profiled, and extensible, which makes it possible to use X3D in very different(75), from high-end visualizations to lightweight applications.

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Most IP layer-based proxy mechanisms, such as network address translation(NAT), only support uni-directional proxy, from the internal network to external network(the Internet). The proxy establishes the communication channel by(66)IP addresses. The IP addresses must be(67). These proxy mechanisms prevent applications that must establish return data channels from establishing their data channels, such as, multimedia applications. IP layer-based proxy mechanisms need additional software(68)for each application that uses(69)channels. SOCKS identifies communication targets through domain names, overcoming the restriction of using private IP addresses. SOCKS can use domain names to establish communication between separate LANs, with(70)IP addresses.