An assessment of network utilization statistics is included in the VoIP Readiness Assessment for one basic reason: your voice over IP traffic will have to share device CPU time and network bandwidth with all your other application traffic. Monitoring network utilization is important for two main reasons:
The chances are extremely good that your enterprise will exhaust all of its existing bandwidth—and probably sooner rather than later. Even without additional users, there will be new, bandwidth-hungry applications running on your network in the coming months.
Different types of network traffic not only use widely varying amounts of bandwidth, but they use it in different ways.
For example, when a network user in the CEO’s office downloads an Internet radio broadcast of a baseball game, the traffic flows over the wires in a steady stream and demands a constant amount of bandwidth for several hours; otherwise, the audio would be choppy and difficult to decipher. By contrast, when this same user downloads an .mp3 file or a large PowerPoint presentation, the traffic grabs a great deal of the available bandwidth for a fairly short period of time. So if this user tries to simultaneously perform both tasks, their differing requirements may clash: the amount of available bandwidth may affect the speed of the download or the quality of the audio stream.
When different types of network traffic compete for bandwidth, VoIP traffic is seldom the victor. The RTP protocol it uses does not resend packets that are lost by the receiver, so lost data may mean a lost syllable. And VoIP traffic is extremely delay-sensitive; your conversation will sound like you are using a walkie-talkie—or worse—if delay levels are too high. When a phone conversation has to compete in a router queue with the CEO’s .mp3 file, the utilization level of your router may become an issue for your VoIP implementation.
The Utilization assessment is crucial to recognizing places where upgrades will be needed to ensure the network supports high-quality VoIP calls.
One key to getting a helpful assessment of your network’s VoIP readiness is correctly setting up the Utilization assessment. First, you may want to check the result ranges for utilization monitoring. These ranges set network- or enterprise-specific standards for peak and normal utilization levels and determine what's rated “Good,” “Acceptable,” or “Poor” utilization on this particular network. The default selections are appropriate for industry-standard VoIP implementations, but you should check to make sure they are realistic for the network you are assessing.
You can configure Utilization assessment result ranges by clicking Result Ranges from the Options menu in the Assess Utilization view. For more information, see Section 5.2, Determining Assessment Result Ranges.
When you create a schedule for the Utilization assessment in the Set Up view, be sure your schedule will give you an accurate sense for how much of your capacity is already being consumed on a typical workday. Bandwidth Modeling can then help you calculate how much more of your capacity VoIP traffic will demand.
Set the speed for WAN and LAN links before starting utilization monitoring by editing them in the Inventory Network Discover view. There may be a difference between a link’s configured data rate and its actual capacity. With the exception of frame-relay links, Vivinet Assessor finds the link’s actual capacity, which may be much higher than the configured data rate, from utilization monitoring. This disparity could skew the utilization results. For more information, see Section 3.3, Working with Discovered Routers, Switches, and Links.
If you can, perform utilization monitoring on especially busy days, such as the day of the month when the Accounting Department is sending out its payroll updates. You need to know what your utilization is like at your busiest times of day and days of the week—what Cisco Systems calls “Busy Hours Traffic” or BHT—so that you can plan for adequate or, even better, excess capacity to be available if needed, at any time.
Or run a VoIP Quality assessment while the Utilization assessment is running. The extra traffic from the simulated calls will give you an accurate indication of utilization levels when VoIP is actually deployed.
For more help in capacity planning, see Section 6.1, Understanding Bandwidth Modeling.