Since a passive TAP is not powered, it would be unaffected during a power outage and the packets (originating from a source that still has power) would continue to flow. During a power outage, an active TAP cannot regenerate the signal, so it becomes a point of failure. From a highlevel perspective this would appear to be a positive feature. There is no split ratio consideration because the TAP receives the message and then retransmits it to both the network and monitoring destinations. They require their own power source to regenerate the signals. Impact of the TAP (the actual TAP signal loss)Īctive TAPs are not passive. Light loss within the cable plant (prior to TAP insertion)Ĥ. Receiver sensitivity (residual light seen at the other end)ģ. Transmit power (the starting light signal)Ģ. To quickly summarize light calculations determining passive TAP placements, there are four primary considerations that come into play:ġ. As a general rule, Gigamon does not recommend using a 70/30 split ratio for 10Gb multimode infrastructures as the light margins are too low for the monitored traffic. Best practices dictates running the numbers for each installation. As an example, the entire power budget allocated for some short-range 40Gb transceivers is less than 2 dBm. The 1Gb example shown above provides for a much larger margin than higher-speed optics such as 10Gb, 40Gb and 100Gb. However, the user should be aware that all environments are different. So there is ample margin to insert a 50/50, 60/40, or 70/30 split ratio TAP into this environment. The TAP with the highest Maximum Loss in Figure 6 is 6.2 db (including connections to the TAP). Thus with a Power Margin of 6.465 dB, a TAP will fit nicely into this network. Total Cable Plant Loss = Cable attenuation + Connection loss =. Plugging in the worst-case numbers into the original equations, we would come to the following conclusions:Ĭable Attenuation (10 meters) = 3.5/100 =. 035dB/10mĬonnection loss of multimode connectors =. If we were to pull numbers for a 10 meter run of OM2 multimode fiber running 1Gb (according to IEEE 802.3-2012 section 3 specifications) we would find:ġ000BASE-SX Transceiver Average Launch Power (Min) = -9.5dBmġ000BASE-SX Receiver Sensitivity = -17dBMĪttenuation rates of multimode cable (for 10 meters) = 3.5dB/Km =. An alternative method is to take the worst-case scenario and plug in the minimum numbers as established in the IEEE specifications. Whenever possible, it is best to run the calculations using the actual numbers from the transceivers and cables in use. Power Margin = Additional power that could be consumed while still providing a valuable signal = Power Budget – Total Cable Plant Loss Total Cable Plant Loss = Cable Attenuation + Connection loss = (a – b) + (b – c) + (c – d) Power Budget = Transmitter Power – Receiver Sensitivity = a – eĬable Attenuation = Decrease in signal strength due to absorption and scattering per kilometer of a given cable type = b – cĬonnection Loss = Signal degradation due to connectors in the system = (a - b) + (c - d) The above chart shows the assumed loss associated between two endpoints with a transmitter at one end and a receiver at the other with two connectors (at each end). In addition, Gigamon data sheets for TAPs describe the maximum acceptable network and monitor loss values (including connections) for each split ratio are as follows: Gigamon tests every TAP manufactured and provides the actual tested loss values with each Gigamon-branded TAP shipped. When light levels are marginal, the safe option is to move to better optics offering higher safety margins. The most common split ratio deployed in networks today tends to be 50/50, provided the proper light levels are available. Speeds such as 10Gb, 40Gb and 100Gb have different technical requirements and tend to use more of an even split ratio such as 50/50 or 60/40. The concept is to allocate more light to the network to reduce the risk of dropping network traffic. For example, a common split ratio for traditional 1Gb short-range links is 70/30 where seventy percent of the light continues to the network and thirty percent is allocated to the monitor port. The first number is designated as the network percentage, the second number is the monitor percentage. The split ratio is written as a combination of two percentages. The proportional share of light for each path is known as the split ration. Regardless of the method used, the passive splitter physically diverts a portion of the light from its original source.
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