In recent years, PON (passive optical network) access technology has been widely adopted by major telecom operators due to its advantages of no light source throughout the transmission process, large bandwidth capacity, high transmission rate, low cost, easy installation, and easy maintenance. In the PON system, the location of the OLT device node affects the entire ODN (optical distribution network) network layout and needs to be planned as a priority.

Overall idea of ​​OLT deployment planning

OLT deployment planning is ultimately about planning for coverage and the number of covered users. There are two main factors that affect OLT deployment: one is the investment in the OLT room, including basic civil engineering, supporting power supply and air conditioning, etc. The more OLT nodes there are, the higher the investment in the room. The second is the investment in optical cables for user access, including the investment in optical cables from the user end to the OLT room. The more OLT nodes there are, the shorter the length of the user optical cable, and the less investment in optical cables. Therefore, when planning the PON network, it is necessary to focus on comprehensive considerations from both OLT and ODN. Usually, the deployment of OLT follows the general principle of “large capacity, fewer offices”, and formulates an OLT rolling plan, which is planned, promoted and implemented in stages. For areas with dense users and a large number of users, OLT should be placed in access point rooms with a relatively large coverage area on the trunk optical cable, such as existing end offices or aggregation rooms, and should not be moved down to the community, thereby reducing the investment in the room and operation and maintenance costs.

In rural areas, because the business needs are more dispersed, it is necessary to consider the reasonable environment to place the equipment and power supply and other influencing factors. Therefore, OLT equipment is often placed in existing terminal base stations in the township, and it is not advisable to move it down, unless there is a large demand in rural areas and the users are concentrated, then it can be considered to be placed in living or industrial areas.

2. Principles of OLT planning and deployment

The deployment of OLT should be planned in combination with the current status of the access layer optical cable network and the service development trend of the overall planning. In the early stage of network construction, the coverage area and scope of OLT should be clarified, and the number of OLT nodes in the planning area and the coverage range of each OLT node should be determined according to the user density and the gradual expansion plan, in the spirit of reusing existing equipment room resources and the most economical coverage radius. Generally speaking, the placement of OLT equipment is usually the result of comprehensive consideration of two factors: data transmission demand density and economic coverage radius. The coverage range of a single device is within 2 km to 4 km, and the terminal office capacity is in the range of 20,000 to 50,000. For small towns, this data basis can be appropriately reduced, and the office capacity can be relaxed to the range of 5,000 to 20,000. At the same time, the comprehensive PON network transmission capacity is considered. Therefore, when planning and deploying OLT nodes, it is necessary to consider economy, purpose, coordination and foresight. The following principles apply:

1) In urban areas, the OLT coverage area should be based on urban planning, and should be bounded by highways, railways, rivers and roads that are difficult to cross, and should be comprehensively considered in combination with the actual situation of existing pipeline optical cables. It should be deployed in terminal offices and district centers as much as possible, with a coverage range of 2 to 4 kilometers and a terminal office capacity of 20,000 to 50,000 households, not less than 10,000 households. For areas with large business development potential and relatively high user density, OLT sinking can be implemented to shorten the coverage radius of OLT;

2) In small cities or county towns and large townships, the OLT terminal office capacity should be appropriately relaxed to 5,000 to 20,000 households, with a minimum of not less than 4,000 households;

3) In rural areas, due to the limitation of transmission distance, the maximum transmission distance of the PON system should be planned, and the combination of the existing base station and the computer room should be flexibly selected to complete the coverage by combining FTTB and FTTH. OLT equipment is usually set up in the township module office;

4) Considering network security and other factors, it is recommended that the PON boards of each OLT should not exceed 10, and the number of PON ports should not exceed 80. If the number of PONs exceeds 80, multiple OLTs can be set up in the same machine room or a new OLT can be built in another machine room;

5) OLT equipment should use optical modules (PX20+) that support a larger splitting ratio for networking.

Other issues of attention in OLT planning and deployment

1. Locate the machine room. In general, OLT should be set up in a machine room with its property rights to avoid excessive supporting investment and uncertainty in renting a machine room that will have an adverse impact on network stability. The site selection of the OLT machine room should be selected in a location with convenient transportation, safe and stable surrounding environment, stable and reliable power supply, abundant pipeline routes or convenient construction and construction, and should be as far away as possible from dust, oil smoke and harmful gases, floods and fires, strong noise sources, places where main power lines pass through, prone to lightning strikes, corrosive, flammable and explosive items, etc.
2. Occupied fiber core issues. The site selection of OLT node deployment should not be independent of the existing general machine room to avoid the situation of occupying a large number of relay optical cable cores. It should be close to the trunk optical node on the side of the planned coverage area in the forward direction to avoid the reverse occupation of the trunk fiber core, resulting in confusion in the direction of the fiber core.
3. Planning in the machine room. There must be enough space in the OLT machine room to facilitate the installation of other supporting equipment such as power supply, battery, transmission and ODF of the OLT equipment. The layout of the machine room should meet the principle of shortest wiring distance between equipment and reduce detours and crossing. It should also be convenient for wiring, maintenance, construction and expansion, and the neatness and beauty of the machine room should be properly considered. When the load capacity of the floor meets the requirements, the effective space of the machine room should be fully utilized, and face-to-face single-sided arrangement, face-to-back single-sided arrangement or back-to-back double-sided arrangement can be adopted. When the load capacity of the floor does not meet the requirements, reinforcement measures must be taken. In addition, the main equipment should be arranged in the same column or relatively concentrated, ODF should be arranged separately or relatively concentrated, and large-capacity machine buildings can set up MODF wiring rooms separately.
4. OLT coverage. In urban areas, there are typically 7 live connectors, supporting a maximum transmission distance of 10km at 1:32 splitting. In rural areas, there are typically 5 live connectors, supporting a maximum transmission distance of 12.5km at 1:32 splitting, a maximum transmission distance of 15km at 1:16 splitting, and a maximum transmission distance of 20km at 1:8 splitting.

Conclusion

In summary, the planning and deployment of OLT equipment is crucial in the communication network construction planning. If the selected deployment location results in too many fiber outputs from the equipment and a long distance from the user end, active relay equipment needs to be added. If too many OLTs are densely deployed, the equipment maintenance and operation costs will increase. Therefore, OLT planning, deployment and construction must precede the initial stage of communication network construction. OLT planning and deployment should be combined with ODN network planning, and OLT nodes must be deployed step by step year by year in combination with service development, user distribution and bandwidth requirements to provide support for later service expansion and promote the sustainable development of communication networks.