Net Optics 10_100 to Triple-speed Port Aggregator - Manual (Page 10)

10/100 to Triple-speed Port Aggregator
6
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 gigabyte of data from the full-duplex stream 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 gigabyte 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 .
State 1: Side A + Side B is less than or equal
to 100% of the NIC's receive utilization
Firewall Router
Monitoring
Device 1
1
10/100 to
Triple-speed
Port Aggregator
Using a single NIC each, both
monitoring devices receive all
combined traffic from Side A
and Side B, including physical
layer errors.
Side A
30 Mbps
Side B
50 Mbps
Side A + Side B
80 Mbps
Side A + Side B
80 Mbps
Example: On a 100 Mbps link, Side A is at 30 Mbs 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.
Monitoring
Device 2
B 2 1 A
96443
Figure 2: 80% Utilization