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iTap GigaBit Dual Port Aggregator
4
Memory
All traffi c that passes through the iTap is sent to the monitoring device NIC on
a fi rst-in-fi rst-out basis, including traffi c that is temporarily stored in memory. If
two packets enter at the same time then one packet is processed while the other is
stored briefl y in memory, preventing collisions.
When there is a burst of data, traffi c in excess of the NIC’s capacity is sent to the
iTap’s memory. Memory continues to fi ll until its capacity is reached, or the burst
ends, whichever comes fi rst. For controlling bursts, the iTap has 256 MB of total
memory.
In both cases, the iTap applies a fi rst-in-fi rst-out procedure, processing stored data
before new data from the link. If memory fi lls before the burst ends, the memory
stays fi lled as the stored data is processed – data that leaves the buffer is immedi-
ately replaced. If the burst ends before the memory fi lls, 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
traffi c is 800 Mbps, well below the capacity of the 1000 Mbps NIC.
Figure 1: Side A plus Side B is less or equal to 100% of the NIC’s receive capacity
Each using a single NIC,
the monitoring devices
both receive all combined
traffic from Side A and
Side B, including physical
layer errors.
1
FirewallRouter
Monitoring
Device 1
iTap GigaBit Dual
Port Aggregator
Monitoring
Device 2
Side B
Side A
Side A +
Side B
B
12
A
www.netoptics.com
®
RESET
Network
Monitor
1
2
B
A
Dual Port Aggregator
GigaBit Copper
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