Data network monitoring is becoming more common.
What is a passive TAP (Traffic Analysis Point) within a fibre optic network?
A Traffic Analysis Point otherwise known as an optical TAP provides real-time reporting functionality between two or more points within a fibre-optic network.
Optical TAPs exist in two distinct types, namely active TAPs and passive TAPs. Active TAPs allow manipulation of a signal to the monitoring port and therefore tend to have more specialist applications and specialist transmission and monitoring equipment.
For the purposes of this overview however we shall talk only with reference to the passive versions. As the title of the product suggests, a passive TAP is typically a non-powered unit and is typically used in enterprise data centres for infrastructure and storage monitoring applications.
A passive TAP is a simple device that facilitates the comprehensive monitoring of a single or multiple network ports. Unlike electricity in copper network cables, in a typical fibre optic network, light/data travels only in a straight line and in one direction and this means that a portion of the light can be split out to a monitoring point. A TAP therefore provides access to data on a network without corrupting the data flow or interfering with the smooth running of the network.
Please see fig.1 below to see a TAP in operation where an input (C1) from the host is passed through a TAP not only to the recipient (P1) but also through the (R1) monitoring device.
A modern TAP is created from thin film filter technology and while other cheaper TAP technologies exist, they typically have higher dB insertion losses i.e. the light lost from the origin of a signal to the point at which it is received. Thin film filter technology is therefore the de facto standard and is formed from refraction layers that reflect and transmit light with low performance and insertion losses. Please see fig. 2 for the composition of a thin film filter.
A TAP is selected according to ‘live’ and ‘monitoring’ output signals or split ratios. These split ratios are pre-determined and are usually either 70/30 where the 70 is ‘live’ and the 30 is ‘monitoring’, or 50/50 where 50 is both ‘live’ and ‘monitoring’. On 1 Gb/s and 10 Gb/s networks, a higher live ratio is generally preferred as this higher percentage is dedicated to the network traffic, however on faster networks of, say, 40 Gb/s and 100 Gb/s, a 50/50 ratio is usually deployed to meet power budgets.
As networks advance in complexity and scale, the monitoring of them becomes critical to the system or network administrator. A large enterprise has a requirement to manage the visibility of staggering amount of data and deal quickly with any security or maintenance issues that arise, all without disrupting the flow of information on the network.
A passive TAP can be positioned in the cabling between a host and a recipient device to allow the system administrator seamless access to the traffic and manage any bottlenecks caused by the transmission of millions of transactions, records and files.
By diverting a small percentage of light to the TAP, a minimal dB loss will occur on the network signal strength. It should therefore be noted that sufficient optical power ought to be available for the efficient operation of the network and similarly sufficient power should be available to the TAP port to ensure that the quality of data is not compromised at the monitoring end. It should also be noted that some degradation of signal is to be expected, especially at network speeds of 10 Gb/s and above.
A Bi-directional TAP for 40G and 100G Port Monitoring
The four important factors when choosing a TAP are network speed, wavelength, cable type and link distance, as these will all affect the network’s power budgets.
Singlemode fibre is typically used for longer distances where higher data rates of up to 100 Gb/s are required but can also be used for shorter distances down to 150m. TAPs are available specifically for these applications.
Multimode fibre is typically used for data centre applications and the transceivers use short reach products based on 850nm optical transceivers. New generation transceivers can use multiple wavelengths and operate at wider spectral ranges and these different options will function differently inside a passive TAP.
In a traditional installation, a dedicated TAP panel would be added, and a patch cord would be connected between the TAP panel and the network-patching environment. New generation TAP technology, however, means that the TAP can be integrated into the existing cassette footprint as in the case of the modular approach using our modular MX series, so it is part of a patching environment instead of an additional component in the network.
Apart from the aesthetic value of this integration, a dedicated TAP panel means fewer connections and points of failure and loss within the channel and also that rack space and real estate is conserved.
Cassette based TAPs
With LC ports as the TAP
With Rear MTP port as the TAP
Used within enterprise data centres a TAP offers the following benefits:
Full duplex port monitoring;
No risk of over-subscription;
A TAP can be integrated into an existing cabling infrastructure removing at least two connections;
As a TAP is a passive device which sits invisibly on a network without altering packets or the data flowing through the network;
No configuration required whatsoever;
All data that flows through is captured even corrupted/high security risk data meaning that all traffic is visible at all times.