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毕业设计 外文文献及译文
文献、资料题目: The future of structure cabling systems 文献、资料来源:
Cabling Installation & Maintenance
Magazine
文献、资料发表（出版）日期:
2005.12.1
院（部）:
信息与电气工程学院
专
业:
电子信息工程
班
级:
姓
名:
学
号:
指导教师:
翻译日期:
2012.4.1
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外文文献：
The future of structured cabling systems Which technologies will meet speed and data-transmission requirements in the future? To discuss the future of structured cabling systems, we should spend a moment looking at the past and present practices. Before early 1984, communications wiring systems, as they were then called, were not topics of much discussion. Data-transport speeds were comparatively slow, transmission bandwidth requirements were minimal, and "others" provided the design and installation of the cabling system. The telephone companies took care of the installation and maintenance of the telephone service. When data services became distributed, the cabling system was vendor-specific, and the installation and maintenance of the cable plant was provided by the equipment vendors, or specialized independent contractors. In January 1984, the courts in the U.S. made several important rulings that changed the way telecommunications was provided and distributed. Outside of traditional suppliers of cabling systems, not much was understood about the cabling requirements for communications transport. The proliferation of media and connector interfaces, a lack of standard transmission specifications, and the introduction of cabling schemes by vendors added to the user"s confusion. Bringing order to the confusion and creating generic cabling systems demanded the creation of a standards body whose output would focus on commercial buildings and communications cabling. Since the introduction of the first cabling standard in1991 by the Telecommunications Industry Association/Electronic Industry Alliance (TIA/EIA), that same group has issued a series of standards and specifications regarding most aspects of the structured cabling systems. These standards have provided guidance related to evolving high-speed information transport systems. The vast majority of past and present digital communications, used in the commercial world, has been transported on unshielded twisted-pair (UTP) cabling systems. UTP became the medium of choice because it was economical, perfectly adequate for the applications, and comparatively easy to install versus other available media types. With advancements in network speeds, new transmission specifications for UTP cable
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and connecting hardware have been promoted by manufacturers and eventually endorsed by the standards community. In 1991, the highest rated bandwidth over UTP was 16 MHz; we are now faced with transport speeds demanding transmission bandwidths of 250MHz and beyond. Manufacturers have risen to the challenge and provided UTP components for today"s transmission requirements in excess of 600 MHz. What media and connectors will be available that will be economically feasible at bandwidths of 1G MHz? At what point does UTP become less easy to use and less economical than other media? Future directions As far as we can see into the future, commercial information transfer will consist of both low-speed and high-speed requirements. Applications such as voice, building automation systems, alarms, and security systems will still use low bandwidths. Voice information may change from central office exchange delivery to intelligent peripheral, but bandwidth requirements won"t increase by a large amount. The data packets, with which the voice packets ride, will increase bandwidth requirements. The requirements to transport large amounts of information in shorter and shorter periods of time are changing, and will continue to change. Applications such as graphical data (both schematic and pictorial), scientific modeling, desktop videoconferencing, multi-tiered relational databases and other data-intensive information will drive up the bandwidth requirements. If history is any predictor of the future, we will see information transfer speeds increase at least one order of magnitude per decade. We have seen local area network speeds, on UTP, increase from 10 Mb/s in the mid 1980s to 100 Mb/s in the mid 1990s then to 1 Gb/s in the late 1990s. Today, standards are being written for 10 Gb/s. Where will we be in 2010 or 2020? Microsoft"s Bill Gates is quoted as saying, "We will have infinite bandwidth in a decade"s time." Lawrence Berkeley Laboratory (Berkeley, CA) has projected its throughput needs for 2020 to be 40 Gb/s. What will be its media of choice: UTP, coaxial, shielded twisted-pair, optical fiber, or wireless technology? The two major properties required for any cabling system to be the system of choice are its performance and its relative economics (which include ease of installation). Undoubtedly, fiber and shielded twisted-pair (STP) systems are quite robust and provide greater signal
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headroom than UTP. However, they lag far behind UTP in customer acceptance for today"s applications. But will UTP and other media systems provide the bandwidth for future applications? Will they provide economical solutions? Let"s look at the proposed solutions for future requirements.
Unshielded twisted-pair Currently, standards are being solidified to extend the transmission characterization of UTP to 250 MHz. Many manufacturers are advertising the availability of products that exceed yet-to-be-ratified specifications. Many technical hurdles have to be solved before a Category 6 standard is published. However, it is reasonable to expect that these hurdles - both technical and political - will be resolved. It is generally recognized that UTP has not yet been pushed to its theoretical limits. The question yet remains as to the continued viability of UTP as information speeds increase. If future technology does not improve the efficiency of band-width utilization, then the cost of the electronics, installation detail, and the testing requirements may diminish UTP"s benefits relative to other potential options. It should be noted that currently, there are no plans to develop a standard copper solution for 10 Gigabit Ethernet. Shielded twisted-pair
Shielded twisted-pair is currently characterized at frequencies to 300 MHz. The International Organization for Standardization and International Electro-technical Commission (ISO/IEC-Geneva, Switzerland) is now studying STP for potential publication as a Category 7 standard. The spectral bandwidth will be characterized at frequencies to 600 MHz. Despite being an exception ally good transmission medium, its material and installation costs have restricted its use to special situations and certain countries.
Undoubtedly, STP"s bandwidth limitations have not yet been reached, but as is the case with UTP, economics could be the major stumbling block to its adaptation. The installation of STP requires highly trained installers. North American industry experts doubt that end users or installation contractors will be quick to embrace STP.
Fiber-optic WDM
Wave division multiplexing (WDM) is a new technology that expands the data-carrying
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capacity of optical fiber rather than using a new media type for structured cabling systems. To increase the carrying capacity of fiber, the laser light that carries data through fiber-optic glass can be split into different colors, or more precisely, wavelengths, each of which carries a discrete data channel.
Today, the technology will support up to 40 different wavelengths. In the near future, 128 channels will be available. The best result of this technological development is that transmission facilities for new wavelengths can be retrofitted onto existing plants that connect to fiber already in the ground, which makes it the easiest way to increase bandwidth. This technology will obviate the requirements of additional fiber and will use the existing optical fiber and connectors.
Plastic optical fiber Historically, plastic optical fiber (POF) has been relegated to low-speed, short-distance applications. Recent technical developments of graded-indexed POF have increased bandwidths to 3 GHz/100 meters. But this medium is not endorsed by any standards body because the current technology is limited to a distance of 50 meters at the required bandwidth. Endorsement within a written standard is crucial for market acceptance. It will be perhaps five years before low-cost POF will be commercially available. If and when a standards body sanctions POF, it should offer a more robust system for applications currently served by copper media, at a cost below that of glass optical fiber.
Wireless technology
Much has been written about the prospect of wireless networking replacing fixed-media structured cabling systems in the future. Currently, cost and low bandwidth have left wireless technology with approximately 1% of the number of deployed Ethernet ports. The features of wireless networking are beguiling to those who are involved with the design, installation, and maintenance of structured cabling systems. With wireless, there are no more concerns about running cable to inaccessible locations, and no more concerns about cable types. But for all the magic of wireless networking, there are downsides. Although a standard for wireless networking exists - IEEE 802.11b put out by the Institute of Electrical and Electronics Engineers - complete interoperability among all WLAN vendors remains unattained.
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IEEE 802.11b stipulates an 11Mb/s data-transfer rate. An Australian company has recently developed a wireless system that claims to support 54Mb/s. In an open office plan, propagation of the radio waves may be limited to distances of 200 feet to 500 feet. In a closed-wall office environment, propagation may be limited to as little as 100 feet. Undoubtedly, the cost of wireless networking will be reduced and the bandwidth will increas...