Net Optics PA-CU-AR, PAD-CU-AR manual Application Diagrams Memory Operation, 80% Utilization

10/100 Port Aggregator Tap

Application Diagrams: Memory Operation

All traffic that passes through the Tap is sent to the monitoring device NIC on a first-in, first-out basis, including traffic that is temporarily stored in memory. (If two packets enter at the same time then one packet is processed while the other is stored briefly in memory, preventing collisions.)

When there is a burst of data, traffic in excess of the NIC's capacity is sent to the Tap's memory. .Up to one megabyte of data per side of the full-duplexstream can be stored in memory. Memory continues to fill until its capacity is reached, or the burst ends – whichever comes first.

In both cases, the Tap applies a first-in, first out procedure, processing stored data before new data from the link. If memory fills before the burst ends, the memory stays filled as the stored data is processed – data that leaves the buffer is immediately replaced. If the burst ends before the memory fills, memory clears until the full megabyte of capacity is available, or until another burst in excess of the NIC's capacity requires additional memory..

The following three diagrams illustrate a simple example of a 100 Mbps NIC moving from 80 percent utilization, to 140 percent utilization, then back to 80 percent utilization. .If you have PA-CU-AR model, there is only one monitor port..

State 1: Side A + Side B is less than or equal to 100% of the NIC's receive capacity.

Example: On a 100 Mbps link, Side A is at 30 Mbps and Side B is at 50 Mbps. The NIC receives 80 Mbps of traffic (80% utilization), so no memory is required for the monitoring device NIC to process all full-duplex traffic.

Side A	Active Response Dual
	Port Aggregator Tap
	A B 1 2
	Router	Firewall
	Side B
	1	Each using a single NIC, the monitoring
	Side A +	devices both receive all combined traffic
	Side B	from Side A and Side B, including physical
		layer errors.
	Monitoring
	Device 1
	Monitoring
	Device 2

Figure 4: 80% Utilization