One. Overview
Information network system wiring is the key to one of the cabling system designers therefore must be based on the characteristics of the network, cable performance, system design of integrated planning total investment.Network cabling system design because of poor network performance due to poor performance and low cost make the system down in the wiring system design is the most common, while the price is very expensive, so the optimal design of network cabling is to ensure that the information network with high-quality, highthe basis of performance.
Cable choice should consider various factors, but in the wiring system should first determine the type of cable and wiring using the structure (shielded cable, non-screen cable, optical cable, joining them together or use).Cable typically used with the wire insulation and use one or more layers of plastic skin.The cable is usually from the 2-1800 line of the composition.Large number of cable typically used for backbone cabling systems, they are particularly suitable for low-rate voice and data applications.The cable in the trunk and horizontal (hub-to-desktop) applications in the wiring system in the international standard maximum length of ISO / IEC IS11801 in detail.Note that the maximum length restrictions apply to all media.They do not consider the cable as the network type and protocol used by the different types of performance differences caused by the impact.In fact, the maximum cable length will depend on the system application, the type of network and cable quality.
Table 1 transmission frequency and transmission rate difference
In determining the type of cable before the alignment of the cable to check the available space is very important.Size, weight and flexibility of shielding depends on such factors as whether the use of metal foil or cable jacket preparation, and the number of wires used in the cable.These factors are used with the cable shielding, with reflective material will determine the cable against electromagnetic interference (EMI) capabilities.In the choice of cable, consider the use of shielded cables, reflective material is also crucial.
In recent years, the unshielded twisted pair (UTP) research breakthroughs enabling them to 622Mbit / s or higher transmission rate to transmit data.This makes it possible to use only shielded in the original application of cable to use this cheaper, smaller cable.UTP cable through the cable line to match more closely to reduce EMI interference.This cable is called a balance circuit.In an ideal balance of the circuit, the conductor and the introduction of the noise voltage is zero, so that signal transmission between the lines of there will be no interference.However, this ideal situation is not fully achieved, the cable signal to noise ratio (SNR) is used to measure the noise signal in the presence of cable in the case of signal quality indicators.Because of shielding in the shielded cable, so it is less the balance of features, so good shielding integrity and a good grounding of the shielded cable is very important.High-quality UTP cable without the need for grounding or shielding the entire circuit is not the case can be well balanced circuits.
Light signal transmission through the fiber, so it is not any form of electromagnetic shielding effect.In the transmission rate requires more than 155Mbit / s and needs a longer distance applications, the fiber is usually the best choice.Fiber is small, durable and so on, but it's more expensive than other types of cable high.Most of the LAN cable used is a multi-mode optical fiber.Than high-performance single-mode optical fiber easier to install.In most networks, generally using fiber optic cable as the trunk, while the use of UTP cable used for horizontal cabling.However, with the communication rate of increase and decrease in prices of equipment, the use of fiber optic network directly to the desktop the number growing.For those due to the installation time, space or other constraints is not easy to install cable systems, wireless local area network can be used as an alternative solution.In wireless LAN uses radio waves instead of physical connections to achieve signal transmission, they are particularly suitable for old buildings in the network installation.
II. Cable select
Transmission frequency and transmission rate of 2.1
Transmission frequency and transmission rate is the structured cabling system design the greatest exposure to the two basic concepts.Frequency bandwidth of the cable (MHZ) and the cable on the transmission data rate (Mbps) are two distinct concepts.MHZ said that the unit of time lines in the oscillation frequency of the signal, is a characterization of the frequency of physical quantities, which Mbps represents the transmission line per unit time the number of bits, is a physical representation rate.Transmission frequency that the transfer of information transmission medium to provide the basic bandwidth, the bandwidth depends on the quality of wire used, the exact length of each wire and transmission technology.The transmission rate of a particular bandwidth in the information transmission capacity, transmission performance indicators to measure the device, including attenuation and near end crosstalk, the overall performance of the indicators link with attenuation / crosstalk ratio of ACR to measure.The more bandwidth the more fluid transmission, allowing higher the data rate.Encoding network system established the link between MHZ and Mbps, some special network coding scheme can in a limited frequency band width on the high-speed data transfer.Under normal circumstances the designer is concerned about a particular transmission medium transmission performance in meeting the system under the maximum transfer rate, the following Table 1 through to visually reflect the difference between the two.
Selection should be based on the technical performance of the system, the investment budget, product engineering performance and increase service quality into account.Cat5 +, and Cat6 choice: For the parameters tested Cat5 + limit and the experimental data is similar to UTP Gigabit Ethernet system can support the operation, and different vendors can be interoperable between systems Cat5 +.Cat6 Cat5 + expensive than the price, but 25% of its bandwidth has expanded, showing the transfer rate of increase, Cat6 system is proprietary, which means that each vendor has its unique design elements and performance indicators, the components from different vendorsinteroperability is unlikely, the component indicators are still being studied.Cat6 has been used in a few projects ahead, it is worth noting two issues: the use of Cat6 cable and businesses should choose the same level of production of the connector device, because the CAT6 is a dedicated parts, the manufacturers of the products still can not be exchanged; Cat6 fixed chainRoad and access the test content, in addition to EIA / TIA 568-67 of the content standards, the need to increase: the equivalent far-end crosstalk (ELFEXT), integrated the equivalent far-end crosstalk (PS ELFEXT), return loss (RETURNLOSS), Integrated near-end crosstalk (PS NEXT), integrated attenuation crosstalk ratio (PS ACR) and so on.Currently only the business enterprise Cat6 standards, the general term, prices are often higher than that of the underlying index of the test specifications, but is recognized as acceptance is still a pending problem.
2.2 Screening and selection of unshielded twisted pair
In the wiring system, the transmission medium is the most used variety of cables.Commonly used include copper and fiber cables, and copper for its cost-effective and become the main wiring system, and structured cabling are twisted-pair copper used.Twisted pair is protected by two copper wires with insulation composition.The two insulated wires twisted with each other at a certain density, together, can reduce signal interference.Each wire in the transmission of radio waves radiated by the other root will be offset by the wave line.Twisted pair usually 22 to 26 by two insulated copper wires entwined with each other.Twisted-pair unshielded twisted pair can be divided into UTP (Unshielded Twisted Pair) and shielded twisted-pair STP (Shileded Twisted Pair).And can be divided into aluminum foil shielded twisted pair unshielded twisted pair (FTP), aluminum foil, double-shielded twisted-pair copper network (S-FTP), independent of unshielded twisted pair (STP).Twisted-pair differences in the structure determines its performance, price difference, to provide users with a variety of choices.But how to choose the system transmission media, designers often face a primary issue.Table 2 below the above we make a comprehensive comparison of several twisted pair.
Table 2 Comparison of the price of copper
Of course, the system security technology implemented not only in the link, and can be practiced in the cell, non-shielded system using steel pipe, anti-interference ability has improved greatly.As technology advances, methods and means to solve the problem are also constantly change and improve.
UTP and FTP cables choice; depends critically on the impact of external EMC interference, interference field strength is lower than 3V / m, generally without regard to protective measures, according to the cable test results show that; in the 30MHz band, UTP and FTPthe transmission capacity of similar effect and anti-EMC over time, the FTP isolation than UTP is significantly higher than the 20 ~ 30dB, according to the order of interference signals than the standard size can be selected for FTP, SFTP, or STP cable shielding, such as differentline and shielding wiring devices, grounding requirements for strict FTP, and shall be fully shielded 360 °, or a radiation shield but the source of interference.Also, note that structural changes in the FTP shield the entire cable capacitive coupling, the attenuation of the UTP also increased slightly compared to the same level.Comprehensive cost about FTP: FTP = 1.2 ~ 1.6UTP.Therefore, FTP for serious regional and confidentiality EMC strong places, such as party and government special network, airports, military and industrial enterprises.
2.3 Other factors
Type of device connected to the network and cable carrying the traffic load on the cable is a key factor in selection.Meanwhile, during the cable select should also consider the following factors:
2.3.1 Network hubs and nodes (information oral) between the maximum distance;
2.3.2 in the pipeline and the floor, ceiling, wiring in the available space;
2.3.3 Electromagnetic interference (EMI) levels;
2.3.4 Service equipment for the system changes and the possible use of their way;
2.3.5 system resilience, network scalability;
2.3.6 The life cycle of network requirements;
2.3.7 Cable routing restrictions and restrictions on cable bend radius;
2.3.8 has the potential repeated use of the existing cable installation may be;
2.4 specification
In addition to these qualitative analysis, "Construction and building cabling system design specifications Amendment" (the "Code"), also made the following quantitative requirements:
2.4.1 all kinds of cables and wiring equipment, anti-jamming capability, the use of shielded cabling after the system noise can be reduced an average of 20dB.
2.4.2 The equipment used in various cable wiring principle should meet the following requirements:
(1) When the interference field strength of the surrounding environment or integrated wiring below the noise level specifications of Article 3, paragraph 12.2.1.Interference source signal or computer network signal frequency is less than 30MHZ, but also compliant with the provisions Table 12.2.2, we can use UTP cable systems and non-shielded wiring devices.
(2) When the interference of ambient noise level or cabling above the 12.21 level 3, provides that the source of interference signal or computer network signal frequency is 30MHZ, according to their order of magnitude more than the standard size, were selected FTP, SFTP, STP, such as different shielding systems and shielded cable wiring devices.In addition, the specification requirements of Table 12.2.2 can not guarantee the space, should take appropriate protective measures.
(3) When the user of the system requirement of confidentiality, does not allow the signal out of the launch, or the system can not meet emission targets norms of Article 4, paragraph 12.2.1, should be shielded cable and shielded cable system equipment or wiring.
In summary, what system to use shielded or non-shielded system, according to the application of the owners premises, application requirements, expectations and investment for the future status, etc. into account, select the appropriate system.
III. Focus on growth and flexibility
Most cable companies for their products provides 15-year shelf life.During this time, change is inevitable, but also can not be accurately predicted.The only solution is to design networks to meet the network requirements change and growth plan accordingly.Under normal use conditions, the new network should not be a 15-year building renovation cycle limit system upgrade.The cabling system is designed to withstand more than most of the LAN data transfer rate of 10-15 times the traffic.This will allow the situation does not change the wiring system using the new network technology.Network currently supported by the network application is defined as the minimum index requirements.In some applications, may use Category 3 cable to meet the current application requirements, but in order to meet possible future application upgrades, design, or should be five or over five cables.
Universal wiring and cabling is a structured cabling massive core of the general structure that uses an open platform that supports all the major private networks and non-private network standards and protocols, the use of UTP cable and fiber optic cable as a transmission medium, the use of startopology, using a standard socket for termination.A good routing system should have a simple cable type used to form modular networks, without prejudice to the case of users can easily extend or change the network characteristics.For the rapid development of the company, structured cabling system allows the company has a stable network, the ability to control the operation of expansion, and it allows companies to gradually increase the investment situation in the use of new equipment and new cables.Because all the structured cabling system uses standard components, when laying a new cable wiring system and add new information outlet, which simplifies the task of implementation.High flexibility, small diameter coaxial cable is easier than the alignment, and occupy a smaller space.
With the private network to the open computing system changes, cabling system has gradually shifted from dedicated system utility wiring system.Common cabling system for many different types of equipment to provide services, these devices can be computer and printer, can also be a camera and temperature control devices.The main advantage of generic cabling system is that users can use it to access network equipment from different vendors.It also allows the user to run on the same cabling network of several independent systems.For example, users can create a wiring system, telephone, computer and environmental control systems.Located in each building or buildings within the patch panel is used to implement the computer, peripherals, network hubs and other equipment or the withdrawal of fast access network components.In the structure and layout of the ongoing adjustment of the company, it can save a lot of cost.
IV. Immunity
Each active electronic and electrical equipment may generate electromagnetic interference to disrupt network traffic.With the increased use of electronic devices, this problem is becoming more and more prominent.In the choice of cable and wiring considerations, how to prevent EMI interference to protect the communication is also a very critical issue.In addition to external interference sources may interfere with the network, the in-house multi-pair cable between the lines will interfere with each other on.This interference is called crosstalk interference (cross talk).
There are two ways to measure the performance of cable crosstalk, and crosstalk between lines of the Power Sum crosstalk.Lines of crosstalk between the cables is used to measure the maximum interference generated by the center line of the situation.When multi-line many of the cable on line for data transmission, the cable line on the loss ratio performance of the crosstalk between the value given to large.Power Sum reflect a more realistic case of crosstalk.It is a multi-pair cable in all lines have signals transmitted on the measurement method.For the midline of the number of cable over four pairs of cable, Power Sum is the only test correctly crosstalk performance.
In the system used to measure inhibition of EMI interference indicator is the signal to noise ratio (SNR).The higher the SNR of the network, the network data transmission error occurs the less the risk.Including connectors and patch panels, including all network components, you must have some measures against EMI interference.When using the products from different manufacturers build the network, this is especially to be noted.
When using shielded cable, the cable termination and connector and cable jacket right good grounding feature is a very important point.Any incomplete shielding will reduce the protective effect of the shield, thereby reducing the resistance to electromagnetic interference (EMI) efficiency.The alignment of the cable should follow the manufacturer's recommended methods, and should try to avoid potential interference sources.This should give full consideration to the rapid development of the cable alignment with international standards related to the targets set.For example, in EIA / TIA 569 stipulates that the distance between communication cables and fluorescent lights not less than 15 cm, because the fluorescent lamps are the main sources of interference caused by one of EMI.Like the elevator motor, automatic doors and air conditioning units are all potential sources of interference EMI.The more obsolete equipment, the greater the resulting EMI interference.For those who can not avoid and overcome the EMI interference, the use of a closed metal tube wiring system can provide additional protection.Electromagnetic interference in a specific or sensitive environments, the use of optical fiber may be the only option.
System design, installation, construction supervision and acceptance testing should work together to ensure that the network systems and other electronic devices with electromagnetic compatibility (EMC).Designers in the design of the cable to ensure the technical performance indicators selected, routing and piping are designed to eliminate EMI problems.Manufacturers, the supply of cables for certification, provide the installation of the network system EMC performance guarantee.Installers to ensure the design and specification organizations by the construction, inspection personnel in strict accordance with the specifications and design for test and inspection, to ensure that the information network of high-quality, high performance.