Bare fiber transmission solution for metro backbone network

The metro backbone transport network mainly transmits the circuits between the backbone nodes of the metropolitan area. This part of the circuit is mainly based on 10G and 100G, and the number of circuits between each node is also large.

At present, the metro backbone transport network mainly uses OTN (Optical Transport Network) to realize the transmission and scheduling of services. However, because the power consumption of the OTN equipment is relatively large and the space of the equipment room is occupied, as the number of OTN equipment increases, the equipment space of the existing backbone nodes, the supporting power supply capacity, and the air-conditioning facilities are facing huge challenge.

Feasibility of bare fiber transmission solution

The bare fiber is adapted for carrying a transmission distance of no more than 80km and a point-to-point unprotected circuit. Most of the services carried in the metro backbone transport network (such as Cmnet and IP private network circuits), because the service system itself has protection functions, does not require protection from the transport network. This part of the circuit is also basically not configured when transmitted over the metropolitan area OTN. The protection of the circuit; and the distance between different nodes in the same system in the metro backbone transport network is also less than 80km. Therefore, in the metro backbone transport network, it is feasible to use a bare fiber transmission scheme.

Analysis of current status of fiber optical cable network in backbone transmission network.

The core layer optical cable networking structure of the metro backbone transmission network is a mesh, and the convergence layer optical cable networking structure is like a ring.

circle node

Each optical cable of the existing backbone transmission network is end-to-end, and there is no direct access between the nodes of the optical cable (such as node N and node O in Figure 2). If a bare fiber direct link is to be established, the intermediate node must be jumped through the intermediate node.

Realization and the capacity of the optical cable is generally small, the spare core cannot meet the needs of the bare fiber transmission between the backbone nodes; therefore, to adapt to the bare fiber transmission between the backbone nodes, it is necessary to build a fiber optic cable between the backbone nodes.

Suitable optical cable construction solution for bare fiber transmission.

The following is an example of constructing a 288-core optical cable between the four core nodes of M, N, O, and P to illustrate the construction scheme of the optical cable between the backbone nodes.

The optical cable between the core nodes should be formed into a ring according to the position of each node and the cable construction conditions between the nodes. Since there are different fiber link requirements between any two core nodes, you need to first list the fiber link requirements between each core node.


The shared optical fiber is terminated at each node, and is mainly used by systems with a topology of a ring network (such as PTN and OTN); the exclusive optical fiber is only at the end of a certain two nodes, and provides a direct optical link between the two nodes; The reserved fiber is not reserved at any node.

When a fiber link needs to be added between two nodes in the future, it is only necessary to reserve the fiber at both nodes. According to the core link requirements of each node in Table 1, the fiber core connection relationship between the M, N, O, and P nodes is configured.

Comparison of OTN and bare fiber transmission solution

Engineering investment

When the OTN solution is adopted, the cost of each OTN device is about 500,000 RMB for each 100G port, and the supporting power, battery, and air conditioner are equivalent to about 150,000 RMB for each 100G port. The client device that interfaces with the OTN can use a 10km optical module. The unit price is about 60,000 RMB. The investment in each 100G circuit is about 720,000 RMB.


The bare fiber transmission scheme needs to newly build the optical cable between the nodes. Taking the new 288-core optical cable between the core nodes as an example, when the new length is 80km, the cost of the newly built optical cable line is about 2.58 million RMB. Since the newly-built optical cable has a ring structure, the 288-core optical cable can provide 288 pairs of optical fiber links in a clockwise direction and a counterclockwise direction, and the cost of each pair of optical fiber links is about 0.9 million yuan. At this time, the client device connected through the bare fiber also needs to adopt an 80km optical module, and the unit price is about 100,000. The investment in each 100G circuit is about 209,000 RMB. When the length of the newly built cable is less than 80km, the investment will be reduced accordingly. Room space and environmental requirements.

OTN equipment consumes a lot of power and requires high power environment in the equipment room. Adding OTN equipment often requires the expansion of the DC system of the AC system, switching power supply, and storage battery. OTN equipment has large heat dissipation; it is demanding on air conditioning systems.

In order to increase OTN equipment, nodes often need to increase or expand the air conditioning system. The OTN construction requires high space in the equipment room.

In addition to the installation location of the OTN rack and the branch side ODF, it is also necessary to consider the expansion of the power system and the installation position of the air conditioner. The cooling fan of the OTN equipment and the associated air conditioner generate a lot of noise, and many backbone nodes are adjacent to the residential area, which will cause noise disturbance.

Maintenance and management

The OTN system supports optical power detection, pre-correction/correction error rate statistics, OTDR and other monitoring functions. Through the network management, data such as channel utilization, port utilization, and proportion of different types of services can be obtained. The means of protection, flexible scheduling of services.

Conclusion and Suggestion

Although the OTN transmission scheme has the disadvantages of large investment, large power consumption, and large space occupied by the equipment room, its perfect network management performance determines its irreplaceable role in the metro backbone transmission network.

However, in the face of the large space used by OTN, the space of the engine room, the lack of power, and the problem of noise disturbance, the large-core fiber optic cable is selectively built between some backbone nodes, and the bare fiber transmission scheme is also adopted for the service that has the protection capability of the system itself.

Echo Huang

Echo Huang is an expert wordsmith and marketing professional at Bonelinks with more than 8 years of experience in high technology businesses – fiber optics, IoT, and telecommunication. She is very glad to share industry knowledge and communicate with others.

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