计算机专业英语书本部分文章翻译

计算机专业英语书本部分文章翻译内容摘要：

标准电话线路和传统的调制解调器提供 一般的 的拨号服务。 Although still the most popular type of connection service,dialup service is quite slow, and many users find it inadequate to meet their munication needs. 虽然仍然是最 受欢迎 的连接服务 ,但是拨号服务相当慢 ,很多用户发现它不足以满足需求。 For years, large corporations have been leasing special highspeed lines from telephone panies. 多年以来 ,大型公司 已经从电信公司 租赁 使用 特殊的高速线路。 These linesknown as T1, T2, T3, and T4 linessupport all digital munications, do not require conventional modems, and provide very high capacity. 这些线已知为 T T T T4，这些 线 路 支持所有数字通信 ,不需要传统的调制解调器 ,并提供非常高的 传输 能力 Unfortunately, this type of connection is very expensive. 不幸的是 ,这类 线路的连接费用非常昂贵 For example,T1 lines provide a speed of mbps (over 26 times as fast as a conventional modem) and cost several thousand dollars. 例如 ,T1线路提供的速度为 mbps(速度 超过 26倍常规调制解调器 )，但 成本 却是 数千美元。 While the special highspeed lines are too costly for most individuals,there are affordable connections that provide significantly higher capacity than standard dialup service. 特殊的高 速线 路对于大多数人来说， 太过昂贵。 但如果能够 负担 这笔费用 ,高速线路显然能比普通线路提供更快捷的服务。 These include DSL, cable modems, satellite,and cellular. For a parison of typical user connection costs and speeds,see figure 913 这些包括 DSL、电缆调制解调器、卫星 ,和细胞。 对于一个比较典型的用户连接的成本和速度。 Digital subscriber line (DSL) uses existing telephone lines to provide highspeed connections. ADSL (asymmetric digital subscriber line) is one of the most widely used types of DSL. This technology is widely available in most areas. 数字用户线 (DSL)使用现有电话线提供高速连接。 ADSL(不对称数字用户线 )是一种 使用 最广泛的 DSL。 此项技术仍 使用在大多数地区。 Cable modems use existing television cables to provide highspeed connections as fast as a T1 or DSL connection, at a lower cost. Although cable connections reach 90 percent of the homes in America, all cable nanies do not support cable modems. Industry observers, however. Predict 100 percent availability within the next few years. 电缆调制解调器使用现有的电视电缆 ，以较低的成本 提供高速互联网连接速度 T1 或 DSL连接 ,。 虽然电缆在美国 家庭覆盖率达到 90%。 行业 认识预测，几年内覆盖率就可达到 100% 248 Satellite/air connection services use satellites and the air to download(downlink) or send data to users at a rate seven times faster than dialup connections. While older satellite services could not upload (uplink)or send data to satellites and had to rely on slow dialup connections,newer twoway satellite connections are now available. While slower than DSL and cable modems, satellite/air connections are available almost anywhere that a satellitereceiving disk can be aimed at the southern skies. 卫星 /无线 连接服务使用卫星和 无线 下载 (下行 ),或将数据发送给用户速率比拨号连接快 7倍。 而 老 旧 的卫星服务不能上传 (上行 )或将数据发送给卫星 ,所以 不得不依靠缓慢的拨号连接 ,更新的双向卫星连接现在可用。 虽然低于 DSL和电缆调制解调器、卫星 /无线 连接 几乎可以在任何地方使用 Cellular services offer an alternative for mobile devices and laptops. Using 3G cellular works, devices such as cell phones and appropriately equipped laptop puters can download data from the Inter at 400 to 700 kbps. Uploading data, however, is a much slower 50 kbps. At present,the availability of this service is limited to specific metropolitan areas. In the future, however, this service is expected to be more widespread and to operate at speeds parable to DSL. 蜂窝服务替代移动设备和笔记本电脑。 使用 3 g 蜂窝网络 ,设备 ,如手机和笔记本电脑 的 下载 速度可以维持在 400 至 700 kbps。 但是 上传数据是非常慢 ，只有 50 kbps。 目前 ，此服务仅限于特定的大都市地区 开放。 在未来 ,然而 ,这种服务 相对于 DSL， 应用将更快，更广泛。 DATA TRANSMISSION Several factors affect how data is transmitted. These factors include bandwidth and protocols. 有 几个因素影响数据传输 速度。 这些因素包括带宽和协议。 BANDWIDTH Bandwidth is a measurement of the width or capacity of the munication channel. Effectively, it means how much information can move across the munication channel in a given amount of time. For example, to transmit text documents, a slow bandwidth would be acceptable. However, to effectively transmit video and audio, a wider bandwidth is required. There are three categories of bandwidth. 带宽是一个测量的宽度或容量的通信通道。 实际上 ,带宽意味着可以在固定时间内传输多少数据量。 传输文本文档 ,小带宽可以接受。 但是 ,为了流畅的 传输视频和音频 ,则需要比较高的带宽。 目前， 有三个类别的带宽。 Voiceband, also known as low bandwidth, is used for standard telephone munication. Microputers with standard modems and dialup service use this bandwidth. While effective for transmitting text documents, it is too slow for many types of transmission, including highquality audio and video. Typical speeds are 56 to 96 kbps. 音频带宽 ,也称为低带宽 ,是用于电话沟通 的标准形式。 微型计算机与标准调制解调器和拨号服务使用这个带宽。 能有效的传输文档，但是太慢了，不能满足 ,包括高质量的音频和视频传输。 典型的速度是 56 至 96 kbps。 Medium band is the bandwidth used in special leased lines to connect miniputers and mainframes as well as to transmit data over long distances. Unlik。