Helping You Manage Your Network: Tapped Fiber Cassettes

Data center networks are becoming more and more complex making it more difficult to trouble shoot and balance traffic within LANs and SANs. That is why more network architects and data center managers are deploying Tapped Fiber optic Cassettes (TFC).

Basic TFC Usage TFCs give network analyzers, packet brokers, and other pieces of test equipment access to the fiber link.

So, what are TFCs and how do they work?

First, they perform the function of a typical fiber optic cassette. They aggregate duplex fiber links into multi-fiber backbone trunks and, vice versa. However, they also provide another function.  The optical splitter inside a TFC takes a bit of the laser energy that is flowing back and forth between networking equipment and sends it to a third port. The third port is then connected to network analyzers, packet brokers, or whatever other monitoring tool one may need to use.

Optical splitters are used to siphon off some of the laser energy. Since they are splitting off a portion of the signal, they are making an exact copy of what is coming in and going out of the cassette. That means that no matter what the problem with the network is, the test equipment will get an exact duplicate of the network’s traffic, including corrupt packets. This is something that a mirroring port just cannot do.

Tapped fiber cassettes can be used several different ways, but the two most popular are with crash carts, and with racked test equipment.  Let’s say a problem has been identified with one of the inter-switch links. To debug the problem, a technician rolls up a cart that is equipped with test gear, monitor, and a keyboard. The tech then connects the test gear to the tapped fiber cassette to analyze the problem. For this application, the tapped fiber cassettes have the tap port on the front of the cassette. This provides the technician with easy access to the tap port.

For larger networks and/or extremely critical links that might benefit from, or require continuous monitoring, it might be better to have the test equipment rack mounted. In this case, the test equipment is in a permanent location. Since the network is continuously monitored, the connections to the test equipment are also semi-permanent. This deployment example would use a tapped fiber cassette with the tap port on the rear of the cassette. That allows the tap port to be connected to permanent link trunks just like the networking equipment is.

When deploying tapped fiber cassettes, one needs to be careful with the lengths of fiber between the tapped fiber cassette, the networking equipment, and the test equipment. Because the splitter in the TFC is taking a bit of the laser energy from the link, the length of the link may have to be shorter than it would be otherwise. The actual lengths are dependent on the speed of the link, the type of fiber that is used, and the split ratio of the TFC. Download our technical brief that addresses link lengths from our web site for more detail on deploying TFCs.

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