A Comprehensive Guide To Passive Optical TAP

Updated on Apr 3, 2019 by

Data network monitoring is becoming more and more common. For fiber networks, a cost effective and easy method to enable this is to use passive fiber cassettes with TAP functionality. Whether observing data flow is for diagnostic, monitoring, or maintenance purposes, passive optical TAP cassettes can provide the desired result. Let’s get close to passive optical TAP cassettes to monitor network links together in this article.

What Passive Optical TAP Is

Two types of optical TAPs are available—active network TAP and passive network TAP. The active network TAP uses electricity for operation while the passive network TAP does not. The active network TAP is mainly used for applications that require manipulation of the signal sent to the monitoring port. This is required only for very specialized applications. Passive network TAP is much more common in enterprise data centers and used for applications that require simple monitoring. More detailedly, passive network TAP provides a simple and powerful way to monitor optical networks. And because of requiring no power and having no electrical components, passive network TAP can't be a point of failure when deployed in a production network. And passive network TAP is highly reliable and requires no maintenance. In all, passive network TAP provides access to data flowing across a network, without creating either a location to corrupt data or a prospective point of failure.

How a Passive Optical TAP Works

An optical TAP is essentially a splitter that divides the light into two or more outputs. It can also combine two or more inputs into a single output. For example, in Figure 1 below, the input in Channel 1 (C1) from the host is passed through the TAP to the recipient (P1). The transmitter not only pushes through live traffic to the recipient, it also transmits through the TAP to the monitoring tool (R1).

There are two primary technology options for creating a TAP splitter: a fused biconical taper, or thin film filters, as shown in Figure 2. The fused biconical taper is the older of the two technologies, and while it is easier to produce than thin film filters, it creates a higher insertion loss. The thin film filters, which are made up of a stack of layers of refraction that both reflect and transmit light, are the preferred method. It provides a lower loss that is critical for a TAP solution, since that loss can impact the power budget in the link.

A Comprehensive Guide To Passive Optical TAP

Optical TAP Split Ratio

The construction of a splitter makes the flow of data directionally specific. The monitoring outputs (reflect fibers) only receive traffic. In each TAP, one monitoring/reflect output receives transmitted traffic from the original host device and the other receives response transmission from the recipient device.

A TAP cassette has multiple tap splitters based on the number of designed outputs. Each signal (per TAP splitter) is split to “live” and “monitoring” output signals at a pre-determined ratio - typically 50/50 or 70/30 (70 live and 30 monitoring).

A 70/30 split ratio is generally the preferred method, as it dedicates a higher percentage for network traffic, avoiding any dropped packets. The 70/30 split is most commonly used in 1 Gb/s and 10 Gb/s networks. However, at higher speeds such as 40 Gb/s and 100 Gb/s, the 50/50 ratio is more commonly used in order to meet power budgets.

A Comprehensive Guide To Passive Optical TAP

Benefits of Passive Optical TAP

Passive optical TAPs are much more common in enterprise data centers, as they offer several distinct advantages:

1. TAPs pass all link traffic for monitoring. Even corrupt data will not be rejected, so users are able to see everything in real time.

2. There is no programming or switch configuring required with a passive TAP.

3. They are invisible to the network: they place no burden on the network or any changes to packets or data transmitted through the link.

4. They offer full duplex port monitoring with a transmit and receive path that is scalable at data rates.

5. This means you won’t encounter oversubscription when using a passive TAP.

6. TAPs that are built into the existing patching environment reduce the number of connections required in the structured cabling, taking at least two connections out of the link.

Deploying Passive TAPs in the network

Traditionally, when installing a passive TAP, one would add a dedicated TAP panel and extend a patch cord from the TAP panel to the network patching environment. In contrast, there is now TAP technology that is built into an existing fiber cassette footprint so it can be part of the patching environment, instead of an additional element added to the network. This integration eliminates the need for a dedicated TAP panel and therefore removes two additional connections from the channel.

The integrated design also conserves rack space, since no additional TAP panel is required. With TAP ports on the rear of the cassette instead of front, no patching density is lost.

Passive optical TAPs have become a popular choice for creating network visibility and enhancing network security. They place no burden on the network, and don’t contribute to dropped packets. Passive TAP adoption will continue to grow, with products now available that can be built into the existing patching environment, reducing the number of connections required in the structured cabling infrastructure, and in turn lowering channel insertion loss.


Data center networks are becoming more and more complex making it more difficult to trouble shoot and balance traffic within LANs and SANs. Optical TAP allows network and storage engineers to gather valuable data analytics, which give you a much fuller understanding of your data flow patterns and allow you to plan your technology integrations accordingly. FS.com provide a series of 10G, 40G or 100G network TAP cassette, and is available in single mode or multimode with a 50/50 or 70/30 split ratio.

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