How do you interpret a bandwidth utilization graph?

I have network management tools and am able to generate the bandwidth utilization graph. How do I interpret the graph to determine if the network bandwidth usage is good, oversize or underutilized? What is the best benchmark figure for bandwidth upgrade or downgrade?

Unfortunately, it's not that easy to interpret whether bandwidth usage is "good, oversized or under-utilized," based solely on a bandwidth utilization graph. The best benchmark for measuring if a network link is over-utilized is to measure the impact of the resulting network bottleneck on the critical business applications and users using that link. The following are examples where high and low bandwidth utilization does signal the types of link upgrades or downgrades you would expect.

Business versus Non-Business Traffic

Most companies don't want to invest in upgrading their WAN/Internet bandwidth for a saturated link that is filled up by employees that are Web surfing and listening to Internet radio. Now, if a link was saturated with critical SAP traffic, and this is impacting employee productivity, that is a different story.

Quality of Service (QoS)

While a link may have high utilization, it may not be a problem because priority traffic is still routing properly, and therefore, users are experiencing very little delays. Under these conditions, you could be running at extremely high bandwidths, yet not need to upgrade any of your links. However, if the available bandwidth for priority traffic is starting to reach the capacity of the link, then you may have to start thinking about upgrading your link.

Packet Loss

Although a link may show low bandwidth utilization, packets may be getting lost across the WAN or Internet. Typically, where there is packet loss, users experience slower application performance because data needs to be resent (retransmissions), and the user must wait for this resent data. In this case, there is no need to upgrade the link speed. However, you do need to call your service provider and ask for a fix to the packet loss problem.

Ideal Solutions

The following information is typically furnished by an ideal performance management solution:

  • Real-time and historical trending information
  • Auto-discovery of "Who" and "What" is using the network. Typically, this data consists of the top IP addresses, IP conversations (source and destination IP address), and applications being used.
  • End-user performance measurements including application response time, network latency, and delay, due to retransmissions.

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