Capacity and redundancy space are different

First, it's important to understand that core count design is typically configured based on actual demand plus redundancy. For example, a 24-core optical cable actually requires 12 cores, with 12 cores reserved for backup (this is just an example).

Second, each core represents an independent optical path, and the number of cores directly determines how many independent optical paths the cable can carry.

Imagine two highways: one with two lanes and another with four lanes. If an accident occurs in one lane or construction/expansion occurs, only one lane remains available on the first highway, while the second highway still has three lanes available.

Therefore, 24-core and 48-core cables differ in capacity and redundancy. For a 5-10 year network lifecycle plan, more redundant cores result in faster response times for future expansion and emergency repairs.

Different cable diameters,weights, and supporting facilities

An increase in the number of cores means an increase in the number of cable core bundles. Under the same fiber type and sheath structure, the outer diameter of a 48-core optical cable is usually one specification larger than that of a 24-core cable. Correspondingly, the requirements for duct space, traction tension, junction box capacity, and number of ODF terminals are all higher.

The workload of welding differs from the complexity of troubleshooting

The number of splice points in a 48-core optical cable is twice that of a 24-core cable, resulting in a higher workload and a greater probability of errors in on-site splicing, testing, and labeling management. In scenarios where multiple devices share a cable, unclear color rings and color scheme markings for the core wires can increase the difficulty of tracing and locating the cable later.

The procurement cost differs from the initial investment

Under the same manufacturer and specifications, the price per unit length of a 48-core optical cable is usually higher than that of a 24-core cable. However, the difference is not as significant as the ratio of core count (2 times), because the structural costs of the sheath, reinforcing cores, etc., are shared. In other words, if it is anticipated that there is a high probability of capacity expansion within the next 3-5 years, installing 48 cores upfront is often more cost-effective than starting with 24 cores and adding another if necessary.

Different applicable scenarios

24-core: Commonly used in inter-building cabling, small campus aggregation, and cabling segments before FTTH secondary splitting, or in scenarios where the number of links is relatively fixed and the probability of expansion is low.

48-core: Commonly used in data center backbones, cross-building aggregation layers, data center internal interconnections, or backbone links with clear expansion plans for the next 3-5 years and requiring reserved redundant cores.

How to calculate the required number of cores

First, determine the current actual number of cores in use. Then, list the total number of independent links that this section of optical cable needs to support.

Secondly, reserve redundant cores for faults. In engineering practice, it is generally recommended to reserve 10%-20% of redundant cores to cope with construction losses, mis-welding, and rapid replacement in case of sudden failures, so as to avoid having to dig again or re-lay cables for every minor fault.

Forecast future capacity expansion needs. Reserve a certain percentage of expansion slots based on business growth expectations. If the probability of expansion is high and the timeframe is clear, it is recommended to directly select the next higher standard number of slots.

Round up to the standard specification. Fiber optic cables are usually manufactured according to standard specifications such as 4, 6, 8, 12, 24, 48, 96, and 144. The calculated theoretical core count should be rounded up to the nearest standard level, rather than requiring the manufacturer to make non-standard customizations. This can control costs and facilitate alignment with supporting products (ODF, junction boxes) later.

A simplified reference formula can be written as: Required number of cells ≈ (Current actual number of cells used + Redundant number of cells) × (1 + Expected expansion growth rate), then rounded up to the standard number of cells.

For example

Suppose a newly built office building in a certain industrial park needs to run a main fiber optic cable from the central server room to the building's low-voltage electrical room. The specific details are as follows:

The building has three low-voltage electrical rooms, each requiring two cores (one receive and one transmit) to connect to the central server room, totaling 6 cores currently in use. Following engineering practice, a 20% fault redundancy is reserved: 6 cores × 20% = 1.2 cores, rounded up to 2 cores for redundancy. The client specifies that a security monitoring system and a wireless AP aggregation system will be installed in the building within the next three years, anticipating an additional 4 cores for expansion.

Adding these three parts together: 6 (actually used) + 2 (redundancy) + 4 (expansion reserve) = 12 cores.

However, if there is a more specific expansion plan for this building in the next 3 years, the theoretical value may reach 15-16 cores. In this case, we should directly round up to 24 cores.