TAP 40/100G BiDi Connections

In today’s digital age, the growing dependence on cloud computing, virtualization, and the Internet of Things (IoT) has placed unprecedented demand on the bandwidth of data centers and campus networks. This increase in data traffic has been particularly noticeable at aggregation points of top-of-rack switches in data centers or from leaf to spine in modern architectures. Meanwhile, in campus networks, the uplinks to the core and distribution levels are under increased strain due to the surge in digitization and the expanding quantity of networked devices.

Network managers struggle with these mounting pressures by turning to 40G and 100G connections. But this transition brings with it some challenges. One of the primary hurdles is the cost of upgrading the passive network infrastructure, particularly fiber optic cabling. Additionally, expansions and changes necessitate extended project lead times, making scalability a major concern.

The BiDi Module Solution

In response to these challenges, network professionals have turned to bidirectional (or “BiDi”) modules as a cost-efficient solution for migrating from 10G to 40G or 100G over short distances. The beauty of BiDi modules lies in their ability to work with existing OM3 and OM4 multimode connections with LC connectors.

Unlike conventional modules that need eight fibers, BiDi modules only require two. These modules operate based on passive Wavelength Division Multiplexing (WDM) technology with 850nm and 910nm on both sides. In a 40G setup, each module transmits and receives 20G on each fiber, while in a 100G setup, each module transmits and receives 50G on each fiber. This streamlines the migration process, improves cost efficiency, and reduces project time.

The Challenge of Tapping BiDi

However, as with all technological advancements, BiDi modules have challenges. The main problem lies in monitoring these links. Because of their bidirectional nature, the modules do not support receive-only (Rx-only) operations. This poses a significant concern because any network monitoring or analysis solution connected to the link might unintentionally inject packets back into the network, potentially interfering with network operation and performance.

This challenges network visibility, as traditional network monitoring tools may be ineffective or disrupt normal network operations. Special consideration or specific network monitoring solutions might be necessary to safely and effectively monitor BiDi links.

Monitoring BiDi Links: The Possible Solutions

Despite these challenges, several solutions are available for safely and effectively monitoring BiDi links.

  • Specialized TAP Solutions for BiDi Links: These TAPs are purpose-built to support the bidirectional nature of BiDi links, allowing them to capture network traffic for analysis without disrupting normal operation.
  • Passive Optical TAPs: These devices split the light signal passing through the fiber link, diverting a portion of the signal for monitoring. They operate at the physical layer and do not interfere with the data traffic.
  • Out-of-Band Network Packet Brokers (NPBs): These devices aggregate, filter, and distribute network traffic to monitoring and security tools. They can be used in a BiDi environment to receive full duplex traffic from a specialized TAP or passive optical TAP and distribute it to the monitoring tools.
  • TAP Aggregation and Packet Filtering: This technique combines traffic from multiple TAPs and sends it to a single monitoring tool, allowing traffic from both directions of BiDi links to be monitored simultaneously. Advanced TAPs and NPBs can also filter out irrelevant or duplicate packets, reducing the volume of data sent to the monitoring tool.


As the demand for bandwidth continues to grow, innovative solutions like BiDi modules are paving the way for efficient and cost-effective network scaling. However, they are not without their challenges. Network professionals must know the potential issues posed by monitoring bidirectional links to ensure they can gain visibility into network traffic without disrupting network performance.