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Introduction to Network Bottlenecks
Running programs over the network is likely to result in network bottlenecks. Other causes
of high network activity are, roaming profiles, file copying or large print jobs.
Use performance monitor to create a log and calculate the network utilization.
Network Topics
Network Interface\ Bytes Total/sec
Network Interface\ Bytes Sent/sec
Network Interface\ Bytes Received/sec
Network Interface\ Current Bandwidth
There are several cautionary tales with this performance monitor chart. Let me see if I
can convince you that the maths prove a network bottleneck.
The Bytes / Sec average 913,999. Beware, System Monitor never
uses thousand separators which make the figures awkward to read. I
have often revisited the data because I was out by a factor of ten.
For example, at a glance you could mis-read 913999 as approximately 91,399 or
even 9,1399,999.
Diagram 1
You may think that just comparing the red line (Current Bandwidth) with
the white line (Bytes /Sec) proves that the network is at full capacity. On
closer inspection of the Scale, you realize that the red line is 10x bigger than the white
line. Now you may revise you estimate and believe that the network is only running at 10%
of capacity.
However, there is one more factor, the red line is in bits while the white
line is in
bytes. 1 bytes = 8 bits. When you compute all these factors, the network is actually running at
73%.
Summary
White Line Bytes /Sec = 913,999 bytes x 8
White Line Bytes /Sec = 7,311,992 bits.
Red Line Current bandwidth = 10,000,000 bits
Network Utilization = 73.12%
One of the amazing features of the original ethernet network is that only one
machine can transmit at a time. Once the network reaches 30% capacity,
pure chance means that two machines try and send a packet at the same
instant. The result is more and more collisions start
happening, this leads to re-transmissions and a slow down of network
traffic.
Networks bottlenecks occur at surprisingly low levels of utilization.
40% would normally be considered a bottleneck, and the only reason that I
got a higher value was that there are only three machines on my test
network. The more machines the greater the risk of collisions from two
machines wanting to transmit at once. However, with modern production networks two items of technology have alleviated the above bottleneck problem:
a) Switched networks replacing hubs
b) 100MB
network cards replacing the old 10MB cards.
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