Net Optics 96542iTP, 96547iTP manual Memory, iTap GigaBit Dual Port Aggregator, Side A, Firewall

iTap GigaBit Dual Port Aggregator

Memory

All traffic that passes through the iTap 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 iTap’s memory. Memory continues to fill until its capacity is reached, or the burst ends, whichever comes first. For controlling bursts, the iTap has 256 MB of total memory.

In both cases, the iTap 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 immedi- ately replaced. If the burst ends before the memory fills, memory clears until the full memory capacity is available, or until another burst in excess of the NIC’s capacity requires additional memory.

The following diagrams illustrate a simple example of a 1000 Mbps NIC mov- ing from 80% utilization to 140% utilization, then back to 80% utilization. In this example, Side A begins as 300 Mbps and Side B is at 500 Mbps, The aggregated traffic is 800 Mbps, well below the capacity of the 1000 Mbps NIC.

Side A	iTap GigaBit Dual
	Port Aggregator

A	Network	B	1	2	Dual Port Aggregator
					GigaBit Copper

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Router

Side B

Side A +

Side B

Monitoring

Device 1

Firewall

1Each using a single NIC, the monitoring devices both receive all combined traffic from Side A and Side B, including physical layer errors.

Monitoring

Device 2

Figure 1: Side A plus Side B is less or equal to 100% of the NIC’s receive capacity

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