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With the development of IT technology, the campus network has become the essential infrastructure of the school under the background of modern education, and it has become an important way and means to improve the teaching, scientific research and management level of the school. Especially in the context of the current country's active promotion of educational information reform, many schools in the country are actively planning, building and perfecting the campus network. Among them, the construction of Chinese education and scientific research computer network directly promoted the development of campus networks. China Education and Research computer network has formed more than 900 educational institutions and scientific research units, more than 160 cities across the country, users reach more than 8 million people, become the country after the telecommunications public networks of the second largest internet. Since 2001, the Ministry of Education has officially started the school-pass project of primary and secondary schools, and the comprehensive construction of campus network has been kicked off.
In this context, how can the construction of campus network cabling System be considered in a more strategic and integrated way? How to plan, step, subregion and stage reasonable planning? How can you best avoid short-term, repetitive low-level network construction? How to coordinate the contradiction between the rapid development of local area network and the actual application demand from the angle of wiring? These are questions that we should seriously explore. The author has long been engaged in local network wiring work, has presided over a number of large and medium-sized campus network Cabling System implementation work, quite a lot of experience, now on the following several hot issues, to talk about their views:
L, campus topological structure design
The IP based local area network solution is now dominant in the campus network solution, and the IEEE802.3 series protocol is the core foundation of the campus network. Therefore, when we consider the campus network construction, we should be sure that layered star structure is the best choice for the topology of campus wiring. I have also met individual schools, the whole or part of the campus to the network operators to carry out the design, implementation and operation. In this way, a small number of network based on the SDH transmission mode of metropolitan area network also exists. However, from the point of view of national implementation of education industrialization, such a model of campus network construction is unreasonable. With the strength of the colleges and universities continuously enrich, so the practice of quick success will be less and more, will not become the current stage of the mainstream campus network construction.
Usually, the topology structure of the new large campus network usually adopts the core layer (level), the convergence layer (level two), the access layer (level three) and the star network structure above the three level of the edge access layer. Some schools have built network expansion, can also be based on their own characteristics, step-by-step implementation. In particular, such as the domestic use of more than 100M FDDI, 155M ATM and other backbone networks, can be logically adopted by the ring or tree-type model to deal with, not only the use of existing resources, but also for the future development laid a good foundation. Of course, when considering the overall topological structure, the complexity of the topological structure is reduced from the macroscopic point of view. Under the premise that the distance, the speed, the network management and so on can meet the sufficient demand in a certain period of time, the operation cost of using single level simple structure must be the lowest. In particular, early network technology as the backbone of campus network, can only meet the low speed of data communication requirements, the campus network, networking technology, networks structure is far away, many of the domestic campus teaching building or dormitory layout determines the complexity of the network, not suitable for the implementation of network cabling optimization, the old campus of individual schools have a long history, The low available space in the old buildings determines that the network is not easy to use the distributed structure. Therefore, the optimization of network topology design and product selection put forward higher requirements. (Computer science)
A lot of campus network consider its layered star structure, it is easy to ignore the harm caused by network single point connection. The author suggests that the physical link backup problem of network backbone should be considered when the topology is considered in large campus network. Physical link backup not only refers to the number of optical fiber backup, but also should include its cable routing backup, as far as possible to avoid the single point of optical cable failure caused by the overall network paralysis problem.
2, the choice of campus backbone fiber
Campus network applications mainly include: Internet access, distance education, video on demand, multi-media teaching, school office automation, campus card, Campus IP phone, book information inquiries, research high-speed network, campus network backbone of the information flow is very large. For backbone networks, it is absolutely necessary to build and maintain a large capacity channel that is suitable for now and can be geared towards the future, and its design must be as reasonable and flexible as possible.
From the results of campus network implementation at home and abroad, the choice of optical fiber from the physical structure is mainly Single-mode (8.3/125μm) and Multimode (62.5/125μm, 50/125μm) two kinds of fiber. Single-mode fiber has the advantages of high transmission bandwidth, long transmission distance, high scalability and low price of optical fiber, and multimode optical fiber has the advantages of easy maintenance, wide application and low cost of the whole network. From the current situation of LAN application at home and abroad, the author thinks that it is a reasonable choice to use the form of single mode and multimode to lay the backbone fiber network in the campus network. This can avoid weaknesses, both Low-cost network high-speed applications, but also to meet the future development and other weak system signal transmission (such as cable TV signals, etc.) needs. Especially in recent years, some foreign mainstream wiring companies, actively advocated a new generation of high bandwidth multimode fiber (NGMMF) gradually to the practical, its ability to provide the transmission bandwidth and distance is very close to the current Single-mode fiber, while the overall network cost is significantly lower than single-mode fiber. For example, the cabling giant American Avaya Company since 2000 in the domestic push lazrspeed fiber average bandwidth per kilometer 2000mhz@850nm, its transmission gigabit Network (1GBASE-SX) distance of 1km, The transmission of the million-gigabit network (10GBASE-SR draft) reached 300m, very close to the current single mode fiber in the domestic practical application level, and its network equipment fiber module price is only the same type of Single-mode module 1/3 (in Cisco Gigabit SX/LX Module for example). Of course, the current high price of NGMMF fiber (usually many times the price of common multimode fiber) is a major obstacle to its large-scale promotion, but believe that with the domestic large-scale application, the price will gradually be accepted by the majority of users. This year, Canada's NORDX/CDT company also launched a similar product shortly thereafter.
The author has also tried some of the domestic small optical cable factory production of low-cost fiber optic cable, these fibers are mostly used in domestic inferior quality of the defective fiber made, its usual price of 5 yuan (4 cores/meters). The so-called cheap no good goods, this optical fiber in the network low speed short-term application effect is fair, but it is difficult to ensure stable long-term high-speed applications. Information Industry Department of Information products Quality supervision and testing center has been associated with the Department of some schools through the network has done some random inspection, found that the network "bad name" phenomenon is very serious, an important reason is that the loss of optical fiber transmission is severely exceeded, the gigabit fiber backbone of the actual throughput far lower than the network design indicators.
3. Optical fiber connecting device
The majority of campus network and even local network wiring engineering is still accustomed to using St interface as the standard of optical fiber connection devices. However, in the face of optical installation, not only encountered the problem of installation speed, connection costs and loss performance requirements are often a problem for the construction staff headaches. Fast, cheap, easy to install optical fiber tool Small (SFF) connector also came into being. SFF is not only compact, but, like most connectors, allows at least two docking. SFF is much smaller than conventional fiber optic connectors, and it is the size of the 8-core five-wire cable connectors we normally use. The current mainstream SFF standard products include: MT-RJ, LC, VF45, lx.5, Opti-jack and SCDC-SCQC, performance statistics are as follows table. SFF universality can be far higher than the traditional St and SC, and the production process complexity is not high, some products such as LC Head sales price is even lower than St and SC. How to choose a suitable SFF connector? In the face of many choices, we must be clear about the following issues: first, fiber optic connectors can be compatible with Single-mode and multimode fiber? Secondly, does the optical fiber connection device have good price/performance? Again, does the optical fiber connection device have good system compatibility with the network active equipment? Finally, the supply channel problem of fiber optic connection device? Is the domestic spot, or foreign futures is worth our attention to the problem.
SFF Fiber Connector Product Information
4, indoor twisted-pair wire
According to the authoritative data statistics, more than 70% of the network fault is caused by twisted pair, the author is convinced that this sentence. Believe in systems integration of peers, often encounter some "inexplicable" problem. For example: Network time and time pass; Close to the time pass, a slightly longer distance (are not more than 100M); 10Mbps Normal, 100Mbps is not normal; the number of workstations, the task is not too busy and use or Super Five line, can network speed is surprisingly slow and so on.
Twisted-pair technology was born in At&t in the middle of 80, and was introduced into China in the middle of 90, during the period of roughly four large-scale applications. First of all, from the mid-80 to the early 90, with the popularity of 10Mbps Ethernet, three types of unshielded twisted-pair cable replaced a variety of unbalanced cables (such as coarse, thin coaxial cable, etc.). Then, from the beginning of the 90 to the middle of 90, with the promotion of 100Mbps Fast Ethernet, five types of unshielded twisted pair have replaced three kinds of market. Since then, by the end of the 90, with the potential of 1GBASE-T network fully tapped, super five unshielded twisted pair has become the mainstream of the wiring market. Now, with the formal release of the Tia/eia six type of unshielded wiring standards, 1GBASE-TX officially launched, six types of unshielded twisted-pair has gradually become the preferred product of key items. Through this process, we can clearly see the speed of cabling development is amazing. The so-called factory wiring 15 or 20 technical level is not backward guarantee is completely unrealistic, select the type of twisted pair must fully consider the future of a certain period of time the development of network applications.
The author thinks that the choice of campus network wiring system in the current situation, should be very cautious to different network application level of the region to distinguish treatment. For example, student dormitory area, teaching area, teachers dormitory area, office area, logistics area and other networks based on the Super five twisted pair of dual-stranded gigabit backbone combined with hundreds of desktop, to deal with the current application has more than enough, the future can be a smooth transition to gigabit to the desktop, the real meaning can meet the next 10-20 years of network application requirements. However, in areas such as library area, Network Center, Scientific Research Center, multimedia classroom and so on, it is worth discussing whether the system of super Five is unified or not. The author from the construction of several large campus network construction project as a whole process, think that in the case of capital conditions, it is necessary in the initial design of these areas to consider the use of six types of cabling system to meet its future for a considerable period of time demand for bandwidth.
On the whole, the Super five cable is a very mature industrial products, the current network application of the overall cost-effective is very high, suitable for the campus network of large-scale procurement. But it is worth noting that the impostors of counterfeit and shoddy products must be carefully protected. In the fakes flooded the computer city, from hundreds of yuan to hundreds of of the various types of true and false twisted twisted wire dazzling. As a user, how do we identify the true and false?
First of all, to determine whether a super five-type twisted pair is counterfeit foreign manufacturers. Domestic users usually use imported brands of Super Five Cable, the reason is that the foreign Super five cable quality is better than domestic quality, product construction rich degree, the project is easier to pass acceptance. Therefore, some illegal manufacturers in China began to imitate foreign twisted-pair lines. How do you sign a fake? One of the technicians who worked in the Customs and Excise Department told a simple test method: The original imported twisted-pair skin PVC materials are usually used in the United States du Pont (du Pont) chemical materials, plastic skin tensile elasticity, a network of lines in half, if you can immediately bounce back, basically you can think that this network cable for the real. Many domestic manufacturers of counterfeit cable, the general use of Low-cost low-quality PVC materials, finished twisted pair of skin or thin or thick, but usually very low tensile capacity.
Second, you have to actually test the speed. "Trickery" phenomenon in the twisted-pair market also exists, now set up a network generally use more than five pairs of twisted-pair, five types of twisted-pair line has been eliminated products. However, some irresponsible twisted-pair manufacturers in the Super five-type twisted pair become the mainstream of the market, they will be unsalable five types of line packaging change the label and packaging, often dubbed over five types of telecommunications broadband line for sale. This type of inferior super five linear energy is obviously lower than the same normal cable, the implementation of the construction business to leave a very small, the actual speed after the implementation of the network usually can only reach five types of wiring level. This kind of false means is very concealed, the general user is difficult to discover.
Finally, the true quality of twisted pair has a certain heat, tensile, flame-retardant, easy to bend characteristics. You can test the twisted pair in a high-temperature environment, and the good twisted pair will not soften when the ambient temperature reaches 35 ℃ to 40 ℃. and the false will; At the same time, in order to ensure the safety of wiring connections, good twisted pair cable outsourcing rubber has a strong tensile resistance, while the false but not; Also, twisted-pair cable using metal copper , some domestic manufacturers in the production in order to reduce costs, in the copper added other cheap metal, its performance is inferior twisted twisted wire core than normal obviously to hard, not easy to bend, construction process easily broken. In addition, high quality twisted-pair sheath also has a flame-retardant function, ul cm-level twisted pair with horizontal non-combustion characteristics, UL CMR-grade twisted-pair line with horizontal and longitudinal non-combustion characteristics, UL CMP-level twisted pair with PVC material high ignition point temperature under the flame retardant characteristics. The fakes are made of inferior materials and can be tested in person when purchased. North America, South America, Asia Pacific and China are based on North America's cable Fire standards UL and NEC (National electronical Code), while some parts of Europe, low halogen or low smoke halogen-free green cable standard, but the type of cable has a low ignition, can be spontaneous combustion, It is unfavorable to the fire protection and the soft and the electrical characteristics of the electric cable are more vulnerable to the construction damage than the fireproof gate area.
Need to point out, such as Jiangsu Leting Cable Factory, Shanghai Kang Hua cable factory, Jiangsu Zhongtian Cable Factory and other domestic cable factory, has introduced a number of production lines for a number of foreign brand products for domestic fixed-point OEM production, in the IT industry jargon, this is called OEM. I have been invited to visit some of these plants, found that many foreign brands of twisted-pair (including five, five and six categories) are in this production, the same production line made of products, brand different, the price difference is also very large, OEM products are usually the original brand product price of 2 to 3 times times. Therefore, the choice of products must be carefully differentiated, do not think that the choice of foreign brands of wiring, the choice of imported foreign similar high-quality products, to avoid the network wiring construction name is inconsistent. A lot of campus network wiring construction is to spend the original imported money, actually bought affixed with foreign brand label domestic products, wasted a lot of valuable money.
5, work area jumper
Manufacturers often claim that its special jumper for the overall performance of the wiring system, the author believes that the advantages of special jumpers mainly have the following advantages:
First of all, the special jumper once the electrical performance is higher than the manual on-site production products. The same super five wiring link uses the special jumper and the self-made jumper test respectively, usually its channel performance difference is about 30%. Secondly, the special jumper adopts multi-core core (usually 8 cores) and proprietary core fixing process, the physical characteristics, especially the jumper flexibility and RJ45 contact reliability is obviously higher than the manual jumper made by the horizontal single core twisted pair line. Therefore, the service life of the special jumper is longer and the reliability is higher. Finally, the specialized wiring supplier's special jumper's impedance matching performance is better. Wiring factory production standards are usually far higher than the industry standards, the author has visited an international well-known brand research and development laboratory, its wiring channel impedance production standards for 100ω positive and negative 6ω, that is, the brand industrial product impedance error range control in 94ω to 106ω, far higher than the international standard of positive and negative 15ω requirements. Full Channel product application of the same brand product, the coupling performance of different components can embody the standard of laboratory design, minimize the signal reflection caused by impedance mismatch, which will lead to the high rate of switch of network data and greatly affect the speed of actual operation of the net.
But in the practical application of campus network engineering, we find that the drawbacks of the large-scale application of special jumpers are also very obvious. First of all, compared to the manual production of jumper 10 yuan cost, the price of the original jumper is too high. Second, the original jumper specifications are limited, usually only 3 feet, 5 feet, 7 feet, 10 feet and other specifications, the lack of application of targeted. For example, the campus network of staff in the residential building of the jumper in the direction of the more troublesome thing. In addition, the special jumper supply cycle is also a long-standing problem. Because the application of the special jumper is not scale, it causes the retail circulation channel is very not smooth. It is difficult to imagine as a user in order to buy an original jumper and spend 3 months to order from abroad bar!
The author thinks, as an important link of campus network wiring, the jumper problem needs to be analyzed seriously. Under normal circumstances, between the equipment and the management of the room inside the jumper to take into account the number of plugs may be more, the reliability of the product requirements higher. It is recommended to select the original jumper as much as possible according to the port usage rate, and keep a sufficient number of spare parts (usually 10% of the order quantity). Jumpers in the work area can be made by hand, according to the needs of the specific application of RJ45 pliers to suppress their own, the main points of concern are two: first, RJ45 Crystal Head and cable must choose a good quality control of the factory products to the maximum extent to meet the requirements of system impedance matching; second, Manual jumper should pay attention to line to order, in principle, recommend the use of Eia/tia 568B standard, so that the system has better compatibility.
The methods described above are limited to five types of system applications. The campus network uses six class cabling system, when chooses the jumper, only then chooses the specialized six kind of jumper to be able to make the system to achieve the design request, six kinds of jumpers cannot be self-made. But can also adopt step-by-step implementation of the method, temporary use of manual jumper to achieve Super five application standards, the next few years after the network transition to Gigabit desktop, and then order a special six jumper, phased rational application.
6, Work Area panel
The selection of the workspace panel is an easy to ignore problem, and system integrators provide panels that are often functionally and visually passable and difficult to satisfy. As a user, we have the right to choose fine workmanship, full-featured products.
The author has visited a school campus network, the value of nearly 8 million of a set of so-called "domestic leading, international level" of the gigabit Backbone/hundred Mega Desktop Campus network. During the visit, the author fully experienced the luxurious and orderly configuration of the computer room and the regional Management center of the School Network Center. In stark contrast to this, wiring system work area used in the form of simple, innovative domestic counterfeit panels and the school office decoration Style has formed a sharp contrast, unknown to the individual teachers even suspect that the office of such inferior product is really good value for money, all this does not let us be filled with emotion.
Really good working area panels should have the following characteristics:
1. General: High degree of generalization, a wide range of combinations, the use of imported PC plastic as a panel material, good strength, smooth appearance. The panel frame has a right angle (type) arc angle (type) and a variety of styles to choose from;
2. Ultra-thin: The thickness of the panel generally does not exceed 6mm, the product is lightweight, beautiful;
3. Simple: Card buckle connection, installation and convenient, and shielding the installation screws, the appearance of more concise and crisp, even after repeated disassembly can still be closely coordinated;
4. Colorful: The Panel has a variety of colors to choose from, you can meet a variety of occasions, the environment of indoor decoration requirements.
At present, the vast majority of well-known wiring products suppliers can provide imported or domestic GB panels for users to choose. There are two main import panels, one is the United States as the representative of North American style panels, which usually do not include dustproof spring doors, but the use of plug-type dust cover. The utility model has the advantages that the RJ45 module can be installed on the panel in any way 90° or 45°, and has good function in use. Another is the French, German and British products represented by the European style, these panels are usually equipped with dust-proof spring door on the panel and replaceable signage, its products are quite elegant, fully embodies the personality style. Due to the global popularity of cabling products in the United States, European electrical panel manufacturers have also tailored European-style panels for the American wiring manufacturers, which are typical examples of China's first building-Shanghai Jinmao mansion. It is said that the Jinmao tower has installed more than 20,000 points of information, wiring system with a full set of Avaya Super Five products, all of its panels are used in French-style products from Europe.
At present, to Matsumoto electrician led professional manufacturers of domestic panels after years of technological innovation, but also launched a corresponding wiring supporting panels for users to choose. These products usually have a strong appearance and moderate price, but there is still a gap between the manufacturing process and the service life of the products and the imported products.
In addition, there are some small-scale manufacturers in Jiangsu and Zhejiang, the production of counterfeit imported panels, these products are often rough workmanship, poor quality, but cheap. System integrators often prefer to recommend similar products in order to reduce costs, and many schools are less likely to be defensive because of their lack of systemic performance. Seemingly a very small problem, resulting in the entire network cabling system external image damage.
7, lightning Protection problems
Campus network wiring In addition to outdoor cable according to the standard to choose a special outdoor lightning-proof armored cable, outdoor optical cable grounding problem also deserves our attention. There are usually two types of lightning intrusion, one is direct lightning strike, the other is inductive thunder. In general, there is little likelihood that the network equipment in a building in a lightning strike is likely to be installed, usually without the need to install protective lightning-struck equipment. Inductive Thunder is caused by the lightning flow generated by the strong electromagnetic field changes with the conductor induced overvoltage, over current to form a lightning strike. Inductive mine intrusion electronic equipment and computer systems are mainly the following three ways: first, the Lightning ground potential counterattack voltage through the grounding of the intrusion; Secondly, the lightning is invaded by the AC power supply line; Finally, the lightning is invaded by the communication signal line. If you do not manage which form, which way to invade, the network equipment and computer system will be different degrees of damage.
Experts recommend the campus network Cabling System Lightning Practice is as follows: the use of optical cable as the backbone of the network to connect the medium, you do not need to install lightning arrester, can be directly overhead laying. If the use of twisted-pair as an outdoor connection, it is best to choose a dedicated metal armored direct buried cable, or must be buried through pipe laying. In the interior part twisted-pair wire, the best lay in the Equipotential electric metal bridge frame or the metal pipe, the metal bridge and the metal pipeline must connect with the grounding system to be good, the grounding resistance must not exceed 1 Ω. Wiring system can not be shared with strong electric wire bridge or metal pipe. For overhead cables, it is necessary to take lightning protection measures in the network input, such as loading surge arresters, pressure-sensitive resistors, strong filter circuits, etc. to restrain their interference. Common grounding resistance Test instruments include: Italy ht234e digital precision grounding resistance tester, Austrian Geox double jaw multi-function precision grounding resistance tester, France c.a6411-c.a6413-clamp grounding resistance tester.
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