FTTH Optical Fiber Transmission Line FAQ


Fiber to the home (Fiber To The Home, FTTH) is a transmission method of optical fiber communication. It is to directly connect the optical fiber to the user's home (where the user needs)...


FTTH optical fiber transmission line

1. The grounding problem of optical transfer box and fiber distribution box

Answers to questions based on documentation:

(1) Communication industry standard YD/T 5186-2010 "Specifications for Installation Design of Outdoor Cabinets for Communication Systems".

(2) Communication industry standard YD5102-2010 "Code for Engineering Design of Communication Lines".

(3) The national standard GB50689-2011 "Code for Design of Lightning Protection and Grounding Engineering of Communications Bureau (Station)".

(4) Gongxin Bugui [2008] No. 75, Communication Construction Project Budget Quota Volume 1 Communication Power Equipment Installation Project.


1. Are the optical transfer box and optical splitter box grounded?

Answer: "Communication Line Engineering Design Specification" requires that the transfer box (room) must be set with a ground wire, and the grounding resistance should not be greater than 10Ω. There are 2 kinds of understanding:

(1) This regulation only regulates the optical cable junction box, excluding the grounding of the optical fiber splitting box.

(2) The optical fiber distribution box is a small transfer box for user nodes, and the optical fiber distribution box should be grounded.

ftth cable

"Communication Bureau (Station) Lightning Protection and Grounding Engineering Design Specifications" requires that the equipment of the broadband access point subscriber unit must be grounded, and the grounding should directly use the steel bars in the building foundation as the grounding body. Understanding: For example, the wall-mounted optical transfer box and optical fiber splitter box installed in the building only need to connect the grounding lead wire to the equipotential terminal in the building.


2. What is the grounding resistance of the optical transfer box and fiber distribution box?

Answer: The grounding resistance of the ground wire should not be greater than 10Ω.


3. What is the cross-sectional area of ​​the grounding lead?

Answer: The grounding lead-in should be multi-strand copper wire with a cross-sectional area of ​​not less than 16mm2; the protective ground of all equipment in the cabinet should be connected to the grounding collection bar by copper wire with a cross-sectional area of ​​not less than 6mm2.


4. How many grounding electrodes are generally used?

Answer: The grounding electrode refers to a conductor or a group of conductors for electrical connection with the soil (earth) for the purpose of connecting with the ground. One, two or more grounding electrodes are used, depending on the type and conductivity of the soil. When using one of them cannot meet the requirement of less than 10Ω, two or more can be used; the distance between the two grounding electrodes is 5 meters, and the grounding electrodes are connected by a grounding bus.


5. Types and specifications of materials used for grounding electrodes and grounding bus bars?

Answer: The vertical grounding body (grounding electrode) should be made of hot-dip galvanized steel, copper, copper-clad steel, etc. with a length of not less than 2.5 meters. The horizontal grounding body (grounding busbar) should be made of hot-dip galvanized flat steel or copper. The horizontal grounding body should be connected with the vertical grounding body by welding.


When the grounding body is made of hot-dip galvanized steel, its specifications shall meet the following requirements:

(1) The wall thickness of the steel pipe should not be less than 3.5mm. Generally, φ50 galvanized steel pipe is used, and the length is 2.5 meters.


(2) The angle steel should not be less than 50mm×50mm×5mm.


(3) The flat steel should not be less than 40mm×4mm.


(4) The diameter of the round steel should not be less than 10mm.


6. How to ground the optical cable junction box in different scenarios?

Answer: According to the installation method and environment, the optical cable transfer box is divided into four types: outdoor overhead, outdoor wall, outdoor floor, and indoor wall hanging.


In addition to the grounding of the indoor wall-mounted box, the other three types of junction box grounding are calculated as follows:

(1) Install the ground electrode.


(2) Lay the outdoor grounding bus.


(3) Ground jumper.


(4) Grounding grid resistance test.


Indoor wall-mounted optical grounding only counts the engineering quantity of laying single-core power cables.


7. How to ground the fiber distribution box in different scenarios?

Answer: The fiber distribution box is divided into three types: outdoor overhead, outdoor wall, and indoor wall hanging according to the installation method and environment.


The overhead and outdoor wall-mounted fiber distribution box grounding covers the engineering quantity of "installing directly buried ground wires"; the indoor wall-mounted grounding covers the engineering quantity of "laying single-core power cables".


Some operators use loose-sleeve twisted non-metallic strength optical cable GYFTY for the optical cable between the distribution box and the fiber distribution box, and the fiber distribution box is not grounded.


8. How to measure the resistance of the grounding grid (how to operate)?

Answer: The grounding resistance is tested with a "grounding resistance tester". The tester includes:


(1) 1 set of grounding resistance tester


(2) 2 auxiliary grounding probes


(3) One wire each of 5m, 20m, and 40m.


The operation steps are as follows:

(1) Insert the two grounding probes into the ground 20m and 40m away from the grounding body along the radiation direction of the grounding body, and the insertion depth is 400 mm.


(2) Place the grounding resistance measuring instrument flat near the grounding body, and wire it up. The wiring method is as follows:


①Use the shortest special wire to connect the grounding body to the terminal "E1" of the grounding measuring instrument (measurement instrument for three-terminal button) or the common terminal after short-circuiting with C2 (measuring instrument for four-terminal button).


②Use the longest dedicated wire to connect the measuring probe (current probe) 40m away from the grounding body to the connecting button "C1" of the measuring instrument.


③Connect the measuring probe (potential probe) 20m away from the grounding body to the terminal "P1" of the measuring instrument with the remaining special wire in the center.


(3) After placing the measuring instrument horizontally, check whether the pointer of the galvanometer points to the center line, otherwise adjust the "zero adjuster" to make the pointer of the measuring instrument point to the center line.


(4) Set the "multiplier scale" (or coarse adjustment knob) to the maximum multiplier, and slowly turn the generator handle (the pointer begins to shift), while rotating the "measurement dial" (or fine adjustment dial) Adjust the knob) so that the galvanometer pointer points to the center line.


(5) When the pointer of the galvanometer is close to the balance (the pointer is close to the center line), shake the handle faster to make the rotation speed reach 120r/min or more, and adjust the "measurement dial" at the same time, so that the pointer points to the center line.


(6) If the reading of the "measurement dial" is too small (less than 1) and difficult to read accurately, it means that the magnification scale is too large. At this time, the "magnification scale" should be set to a smaller multiple, and the "measurement dial" should be re-adjusted so that the pointer points to the center line and an accurate reading is read.


(7) Calculate the measurement result, that is, R = "magnification scale" reading × "measurement dial" reading.


2. Other issues

1. Port ratio?

Answer: The port ratio refers to the ratio of the total number of final splitter ports/the number of households in the FTTH broadband access design.


2. How to calculate the compensation for electric pole digging, and can the compensation be listed in Table 5?

Answer: This fee can be listed in Table 5 “Construction Land and Compensation Fees” according to the actual expenses incurred by the prefecture and city. If a new pole is set up with a new cable at the same time, it shall be calculated according to (pole pit + cable pit) × unit price/pit.


3. How to calculate the working days for installing the optical splitter?

Answer: Optical splitter is divided into box optical splitter, rack optical splitter, chip optical splitter and miniature optical splitter. Two types are commonly used: box splitter and chip splitter. There are 2 quotas for installing optical splitters:


(1) The TXL6-054 is installed in a rack (box), and the unit technician is 0.2. The quota includes rack-type and plug-in optical splitter installation.


(2) TXL6-055 installation of box-type all-in-one machine, the unit technician is 1.0, this quota includes the installation of box-type optical splitter.


4. Where do the cement, sand, gravel, and machine-made bricks come from? (How to separate the materials supplied by A and B in the table)?

Answer: Cement, sand, and gravel are generally B materials. Divide the domestic material table into two tables: domestic equipment table (supply A) and domestic equipment table (supply B). In Table 2, the time-consuming calculation of auxiliary materials is the sum of the two values.


5. The optical splitter and the optical fiber line are plugged (how to calculate the number, and add the drawings)?

Answer: It is explained in the quota of "Optical splitter and optical fiber line plugging": it is suitable for the plugging of the upstream and downstream ports of the optical splitter and the optical fiber line with an existing active connector. It is literally understood that this work is for the plug-in optical splitter. The principle of the plug-in optical splitter is: after the pigtail with plug and the bare fiber (ordinary optical cable, leather cable) are directly fused in the direct fusion plate, it is not only an "existing active connector", and then inserted into the blade. in the interface of the splitter. There are 2 installation positions for the chip splitter:


(1) Jumper-free wiring in the optical transfer box.


(2) In the chip splitter box.


In the jumper-free optical cable junction box, there is a trunk end area, and the first-level splitter goes up to the trunk fiber area, which is completed by a FC/SC 3-meter fiber jumper. at this time:

The number of optical splitters and optical fiber lines plugged = the number of secondary optical splitters *2.


When the wiring optical cross-connect box uses the ordinary optical crossover and the first-level splitter uses the box type, at the distribution optical crossover, the first-level splitter is treated as a jumper fiber up and down, and the optical splitter is inserted into the optical fiber line. The amount of work connected only occurs in the splitter box. At this time:


The number of fiber jumpers = the number of first-level splitters + the number of second-level splitters;


The number of optical splitters and optical fiber lines plugged = the number of secondary splitters.


The quota of the fiber jumper is TSY1-073 (fiber jumper in the optical distribution frame), and the unit technician is 0.13; the quota of the optical splitter and the optical fiber line is TXL6-056, and the unit technician is 0.03.


There is a point of view that: in the ordinary optical crossover, the pigtail is self-contained by the splitter, and the top and bottom of the first-level splitter are the flanges where the upstream and downstream plugs of the splitter are inserted into the trunk and wiring. On the interface, the amount of engineering is not given to the fiber jumper (man-days), but to the engineering amount of the optical splitter and the optical fiber line. At this time, the number of optical splitters connected to the optical fiber line = the number of primary splitters + the number of secondary splitters*2.


6. When calculating the entire attenuation of the optical link, is the insertion loss of the active connector on the OLT and ONU sides calculated?

Answer: Not counted.


During the test, the emitting optical power and receiving sensitivity of the OLT and ONU already include the insertion loss on the OLT and ONU sides. The ODN attenuation index optical link reference model does not include the insertion loss of the OLT and ONU.


7. Which of the following optical cable programs is correct?

(1) GYTA-12D (2) GYTA-12B (3) GYTA-12B1


(4) GYSTA-12B1 (5) GYTA-12B1.3


Answer: (3), (5) are correct, (4) is not completely correct. B1 in the cable program represents standard single-mode fiber, including B1.1 and B1.3; B1.3 in the cable program represents G.652D single-mode fiber in the standard single-mode fiber.


Two major international system standards: ITU-T International Telecommunication Union; IEC International Electrotechnical Commission


The S in GYSTA stands for loose sleeve. In the naming of optical cables:


(1) D-fiber ribbon structure;


(2) J-fiber tight sleeve coating structure;


(3) C-skeleton groove structure;


(4) X-cable central tube (covered) structure;


(5) T-ointment filled structure;


(6) R-inflatable structure;


(7) C-self-supporting structure;


(8) B-flat shape;


(9) E-oval shape;


(10) Z-flame retardant;


(11) Optical fiber loose sleeve coating structure - no symbol.


8. What is the quota used by the FTTH access project?


A: There are 2 quotas for use:


(1) Ministry of Industry and Information Technology Document, Ministry of Industry and Information Technology [2008] No. 75, Notice on Issuing the "Measures for the Preparation of Budgetary Estimates for Communication Construction Projects" and the relevant quotas




1. Estimates and budget preparation methods for communication construction projects


2. Fixed cost of communication construction projects


3. Quota of construction machinery and instrumentation for communication construction projects


4. Communication construction project budget quota


Volume 1 Installation Engineering of Communication Power Equipment


Volume II Wired Communication Equipment Installation Engineering


Volume 4 Communication Line Engineering


(2) Ministry of Industry and Information Technology document, Ministry of Industry and Information Technology [2011] No. 426, notice and attachments on the issuance of "Supplementary Quotas for Communication Construction Projects such as Passive Optical Networks (PON)".


Before the promulgation of the Ministry of Industry and Information Technology [2011] No. 426 document, China Telecom Group issued two FTTH supplementary documents, which are now invalid. China Telecom [2012] No. 1003 Document "Notice on Forwarding the Ministry of Industry and Information Technology's Passive Optical Network (PON) and Other Communication Construction Supplemental Quotas and Release of Enterprise-related Supplementary Quotas". If you design for telecommunications, you can refer to this document for the amount of work that cannot be found in the two quotas.


9. About the optical cable test?


(1) Relay section optical cable test


In the local network, it refers to the test of the trunk optical cable between the offices.


(2) User optical cable test


In the local network, it refers to the test of the user optical cable from the office point and the optical switch to the user end.


Single core, 4 cores or less, 12 cores or less, etc.


(3) Optical fiber link test


In the local network, it refers to the whole process attenuation test of the link between the OLT side of the central office, through the optical splitting equipment, the optical splitting equipment, and the optical splitting box or optical splitting box closest to the user.


(4) Optical Distribution Network (ODN) Optical Fiber Link Attenuation Test


Refers to the PON port of the OLT refers to the entire attenuation test between ONUs. If the ONU is not installed at the user end, the test is carried out to the splitter end, and it is counted according to the branch ratio of the PON port. Minutes 1:2 to 1:128.


10. Is the installation box quota applied?


(1) Install the optical fiber splitter box and the optical splitter box, apply the TXL6-064 quota, the unit technician is 1.0, and the unit general worker is 0.5.


(2) Install wall-mounted/wall-mounted integrated chassis, apply TSY1-094 quota, unit mechanic 1.0, unit general worker 0.


(3) Install the home-type integrated information (network) chassis, apply the TSY1-095 quota, 0.7 per unit of mechanic, and 0 per unit of general labor.


11. Does FTTH access use primary or secondary splitting?


Answer: Mainly with secondary spectroscopy.


12. What is the relationship between calculating the optical channel optical link budget and the construction team's optical channel optical link attenuation test?


Answer: In the optical link attenuation test of the construction team's optical channel, the fiber redundancy is not included. Fiber redundancy: The increased attenuation due to the degradation of fiber performance at the end of the life of the fiber optic cable.



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