The guiding ideology of building intelligent system construction is that "infrastructure construction is based on the long term, and the application system meets the short-term needs". All systems associated with building decoration and supporting equipment installation are infrastructure. For example, the generic cabling, cabling bridge and pipeline of the building are infrastructure. Once these systems are completed, they are difficult to change. Therefore, it is necessary to achieve a long-term return on one-time investment. As an infrastructure, we should not only meet the current needs, but also consider the needs of future development. We should consider not only the needs of non classified networks, but also the needs of classified networks. This is what we call "infrastructure based on the long term". For the application system, due to the rapid development of network technology and great changes in market price, if the advanced system functions can not play a role at that time after investment and construction, when these advanced functions can be used, their creation has been greatly reduced and automatic devaluation has been formed. Therefore, do not pursue excessive money for the application system, It can meet the needs of about 5 years.

In order to ensure the security of state secrets, the construction owner and the engineering construction company shall implement in accordance with the specific technical requirements of the national confidentiality regulations. In the actual implementation, the following problems shall be paid attention to.

1、 The network design must ensure that the classified network and the non classified network are independent, and they are not allowed to be connected through any equipment and lines.
In the process of bid evaluation, it is found that the private network scheme designed by some companies connects secret related networks with non secret related networks through firewalls, vulnerability scanning, intrusion detection and other equipment, which is extremely wrong.

2、 The selection of classified network wiring type shall be determined by analyzing the relationship between spacing and wiring material type according to work demand, economic power, overall layout of various lines and pipelines in the building.
The classified network wiring project adopts optical fiber, and there is no need for spacing with other wiring; Shielded wire shall be used for classified network wiring, and unshielded wire shall be used for non classified network (including telephone line), with small specified spacing; Both classified networks and non classified networks adopt unshielded wiring, and they are required to maintain a large specified distance. From the engineering practice, both adopt unshielded wiring. Although the cost is low, it is difficult to achieve the specified spacing in the corridor of the building. The secret related network adopts shielded wire and the non secret related network adopts unshielded wire. Its spacing is easy to realize and the investment will not increase too much. It is more economical to adopt this scheme in engineering practice, which is conducive to popularization and construction.

3、 Problems needing attention in engineering design and construction
3.3.1 bridge and pipeline are the basic construction. Once the construction is completed, the relative installation position between them and the heating and ventilation pipe, water pipe, fire water pipe and power line pipe of the supporting installation system is determined. The change of any system position and other positions will be changed, and the quantities are very large. Therefore, it is almost impossible to change the specification and position of wiring bridge unless the building is reconstructed as a whole. Therefore, the bridge construction must implement the construction idea of "based on the long term", so as to benefit from one-time investment for a long time. The following problems should be paid attention to in the specific construction design: first, the specification of the bridge. According to the construction specification of generic cabling, the utilization rate of its space is 50%. Due to the bending and overlapping of wiring, the space occupation can reach 70% with 50% of the wiring volume, and the actual margin is only 30%. Therefore, the margin should be larger in practical application to ensure the needs of future development; The second is the installation position of the bridge. The classified network wiring bridge can only lay the classified network wiring, and another bridge is set for laying the non classified network wiring and other professional wiring. It is forbidden to lay the two types of lines in the same bridge. The distance between bridges is the distance between classified and non classified wiring; Third, when the bridge enters the corridor from the weak current room and leads the metal pipe from the corridor bridge to the information socket, the specified spacing shall be maintained.

(1) The calculation of wiring length is the total distance from the wiring room to the information point. In practice, some people only calculate the length of the cable in the bridge, not the length of the cable entering the room, which is wrong. The reason is very simple. If two lines are laid in parallel, mutual induction will occur. The longer the parallel direction, the stronger the induction signal.

(2) For the surface treatment of bridge, galvanizing is better than plastic spraying and painting. Since the wiring bridge is a complete set of products connected and installed by straight groove, elbow, cross and tee through connecting plate, the surface treatment adopts plastic spraying or painting products, its joint connection is insulated, and only jumper wire is used for electrical connection; There is an insulating layer between the cover plate of the bridge and the tank, so the shielding effect and grounding effect are poor. The bridge with galvanized surface is installed as a complete product to form a fully enclosed shielding groove, with good overall shielding effect and low grounding resistance. There is no big difference in the cost of the two products. Therefore, the bridge with galvanized surface shall be selected.

It should also be noted that although the bridge has shielding effect, its shielding index is an uncertain point, and there is no shielding index for the product itself in the national standard. Therefore, in practical application, it can not be recognized as a shield. As a shielding material specified in confidentiality laws and regulations, it can only be used as a technical auxiliary means beyond the specification to strengthen the shielding and isolation effect and improve the shielding effect. In other words, cable tray cannot be used to replace shielded wiring.

(3) The bridge shall be grounded to ensure that the shielding and isolation of the bridge play a role. However, the bridge cannot be used as grounding wire.

(4)  the wiring pipe shall be metal pipe instead of plastic pipe. According to the requirements of construction specifications, exposed installation and ceiling installation conduits must adopt metal pipes. The pipeline entering the room is generally constructed by the combination of suspended installation on the ceiling and embedded in the facade wall. Therefore, metal pipes should be selected from the construction specifications and from the perspective of improving the shielding and isolation effect. When the metal pipe is used as the threading pipe, the jumper must be made at the joint to make the whole line grounded and play a shielding role.

(5) Selection of information points and embedded boxes. Optical fiber wiring and shielded wiring are adopted, generally one 86 × 86 panel can only be designed with 2 information points. Since the wire diameter and hardness of shielded wiring are slightly larger than those of non shielded wires, the project construction requires an allowance of 5-10cm. In addition, the tail of shielding module is long and occupies more space, so the embedded box is required to have enough space. Generally, it is more appropriate to install two information points according to one panel. 86 is required for embedded box × eighty-six × 60 metal box. If the depth is not enough, it will increase the construction difficulty, and it is also difficult to ensure that the cable has sufficient margin, which is extremely unfavorable to future maintenance.

(6) When shielded wiring is adopted for classified networks, good independent grounding shall be ensured. The classified network itself requires independent grounding, so the shielding grounding of generic cabling must be set separately from that of other networks. That is, the grounding point is independently led from the joint grounding body to the weak current room on each floor as the independent grounding wire of the classified network. Shielding layer grounding is divided into one end grounding and two end grounding. One end is grounded only at one end of the weak current room. When both ends are grounded, the other end is grounded at the information point user box, both ends are connected to the same grounding point, and the shielding layer is continuous. If there are two grounding bodies, the grounding potential difference shall not be greater than 1VR. M.S. (valid values). This is the comprehensive requirement of the shielding system. Otherwise, the grounding wire forms a closed loop, which can not shield the signal, but turn the shielding sheath into a radiator and weaken the shielding effect. Shielding grounding resistance requirements: the resistance of independent grounding body is less than 1 Ω, and the resistance of combined grounding body is less than 4 Ω.

(7)  keep enough space between classified network wiring and power line during construction.