Think Before You Upgrade: Will More Bandwidth Really Help?
Upgrading network connections to higher bandwidth can bring some false hopes.
It is assumed, understandably, that if we go from a 10Mbps link to a 100Mbps link that application performance will improve by a measureable factor. Even non-computer people would think this is logical. However, unless a performance problem is directly related to congested bandwidth on a LAN, WAN, or Data Center link, the application will continue slogging along as it always has.
Before upgrading a link to improve application performance, there are some steps that should be taken.
Conduct a Capacity Planning Assessment
A capacity assessment does more than simply show utilization on a link over a period of time. Utilization graphs can be misleading because often, they are built from data that is averaged over a one to five minute interval. Micro-bursts of utilization will be lost in these averages, and may lead us to think that the link is well below thresholds.
SNMP tools that poll for utilization on a link can also be misleading because they may poll during quiet times, between spikes of traffic on a connection.
Using a tool like the TruView, we can leverage both SNMP and NetFlow data to display the amount of time that a link spends at a certain threshold. If the utilization goes above a comfortable level, the graph will show when and for how long the burst appeared.
Using the Capacity Detail view, the TruView can correlate the time and utilization graph with the Flow data for that connection, which will display the applications that were in use during high traffic periods. In the graph above, we can see that the high utilization measurements directly correlate with an increase in YouTube Video traffic. When this traffic goes away, the connection returns to normal, or average. The Flow data will also show who is responsible for generating this traffic and how many connections were established.
Using this data, we can make better decisions about where and how to upgrade connections, saving precious dollars for the links that will really improve performance.
The next blog entry on this subject will cover the second step engineers should take before trying to upgrade a problem away – Analyze application traffic to determine if the network is the problem.