How to Choose Between Breakout Cables and Trunk Cables

In structured cabling systems—especially in data centers and enterprise networks—selecting the right type of fiber cable is essential for achieving efficient, scalable, and well-organized infrastructure. Two of the most commonly used cable types are breakout cables and trunk cables. While both serve critical roles in high-density fiber environments, their purposes and ideal use cases are very different. Understanding these differences will help you choose the right cable for new builds, network expansions, or equipment upgrades.

What Are Breakout Cables?

Breakout cables are designed to “break out” a multi-fiber connector—such as MTP/MPO—into multiple individual connectors like LC or SC. This allows one high-density connector to feed several single-fiber ports on switches, patch panels, or transceivers.

They are commonly used when you need to connect:

• An MPO port to multiple LC ports
• High-speed backbone links to lower-port-count switches
• 40G or 100G QSFP ports to 10G SFP+ ports

Typical Use Cases

• Connecting a 40G QSFP+ switch to multiple 10G servers: A 40G MPO port can be broken out into four 10G LC connections.
• Upgrading older equipment: Breakout cables allow existing LC-based hardware to interface with modern MPO-based systems.
• Rack-level distribution: Ideal for spreading high-bandwidth connections to multiple devices within the same rack.

What Are Trunk Cables?

Trunk cables serve as the high-fiber-count backbone of a structured cabling system. These cables typically feature MPO/MTP connectors on both ends and are used to transport large volumes of data between distribution areas, network rooms, or data center rows.

They are designed for:

• High-density backbone connections
• Longer-distance routing between racks or rooms
• Future-ready capacity for expanding networks

Typical Use Cases

• Data center spine-and-leaf connections: Trunk cables act as the main fiber “highway” between switching layers.
• Inter-rack connections: Efficient for running multiple fibers between server rows.
• Modular cabling systems: MPO-to-MPO trunks connect structured cabling modules, patch panels, and cassettes.

Breakout vs. Trunk Cables: Key Differences

• Purpose: Breakout cables distribute high-speed ports into multiple lower-speed ports, while trunk cables aggregate many fibers into a backbone or main run.
• Connector Types: Breakout cables typically have MPO → LC/SC; trunk cables are usually MPO → MPO.
• Placement: Breakout cables are used at endpoints or equipment connections; trunk cables run in horizontal or vertical pathways across racks or rooms.
• Scalability: Trunks provide future expansion capacity; breakouts optimize existing hardware.

Choosing the Right Cable for Your Application

Choose Breakout Cables If:

• You need to connect MPO-based high-speed switches to LC-based devices.
• You are upgrading to 40G/100G but still using 10G distribution hardware.
• You want flexible connectivity within a single rack or to multiple devices.

Choose Trunk Cables If:

• You are building or expanding a data center’s backbone infrastructure.
• You need organized high-fiber-count pathways between racks or network rooms.
• You want scalable fiber infrastructure that supports future growth without rewiring.

Real-World Examples

Example 1: Data Center Refresh with 40G Switches

A company upgrades its top-of-rack switches to 40G QSFP+ models but still uses servers with 10G SFP+ ports. A breakout cable allows a single 40G MPO port to feed four 10G LC connections—making it a seamless transition without replacing every server NIC.

Example 2: Building a New Data Center Row

When deploying a new row of server cabinets, the network design calls for a high-density backbone linking each rack to a central core switch. Trunk cables are installed overhead between racks, providing dozens of fiber pathways in a single streamlined run. Breakout cables may then be used at the rack ends to connect to individual devices.

Example 3: Preparing for Future Upgrades

An organization planning to move from 10G to 100G installs MPO/MTP trunk cables throughout the building. Later, when switching hardware is upgraded, breakout cables are added at endpoints to support mixed-speed environments during the transition.

Conclusion

Breakout cables and trunk cables each serve unique and essential roles in structured cabling systems. Breakout cables are ideal for distributing high-speed connections to multiple lower-speed devices, while trunk cables provide the backbone of high-density, scalable fiber networks. By understanding the purpose and practical applications of each, you can design a cabling infrastructure that is efficient, organized, and ready for the future.