Cisco 802.11 Wireless Networking Quick Reference
| You probably already have one of the best network performance tools installed on your network. Microsoft includes System Monitor (formerly known as Performance Monitor and synonymously referred to as Perfmon) since the days of Windows NT. Perfmon provides current, accurate information on thousands of different attributes of your network, and you can easily draft it for WLAN performance monitoring. To start Perfmon, either select its snap-in from the Microsoft Management Console (MMC) or enter Perfmon in the command line. You might already use Perfmon to keep an eye on your wired network. The tool makes it easy to monitor both your wired network and WLAN. Figure 12-2 shows how Perfmon looks when it is first started. Figure 12-2. Perfmon's Opening Display: Ready for Action
Views
Perfmon tracks the data you choose to monitor, and then it offers four ways for you to manage that data. Think of Perfmon as an application with four different tools. These tools are known as views. Each view allows you to display, perform actions, store, and generate reports on the data monitored by System Monitor. Table 12-1 explains the Perfmon views in more detail.
Perfmon can track thousands of metrics. This chapter focuses on network performance in Perfmon. Chart View
To begin monitoring a given metric, start in Chart view (the view when you start the application, as shown in Figure 12-2). In Figure 12-3, we chose Chart view, and then selected Add (the plus sign) from the toolbar to bring up the Add Counters dialog box. Figure 12-3. Adding Counters to Perfmon's Chart View
The following explains the settings selected for this window, as marked in Figure 12-3. 1. This is used to select which computer in your network you monitor. In this case, the computer BLOFELD is chosen.
2. This provides a list of performance objects that you can monitor. These objects include memory, network interface, and server, among many other categories. In this case, Network Interface is chosen.
3. Within the performance object category, you can track certain instances. If you want, you can click the All counters radio button immediately above the list. However, this example tracks only the bytes received by the client computer. Therefore, Bytes Received/sec is chosen.
4. Because the computer BLOFELD has different network interfaces installed, you have the option to select which network interface you want to monitor. The interface you choose is the interface to the wireless network. (Here, the connection is bridged so it shows as MAC Bridge Miniport, although it contains the Wi-Fi connection.) Again, the option to monitor all interfaces is presented with a radio button (All instances).
5. When the monitored items are selected, click the Add button.
6. If you need an explanation of what the counter monitors, click Explain for a brief description. Note You could also click on the icon that looks like a plus sign at the top of the window.
If you care to add more instances to your monitor, use the aforementioned steps. When you finish, click the Close button. After you select the items you wish to monitor, Perfmon looks like the image in Figure 12-4. When Perfmon runs for a short time, you can see how well your client devices fare. If they do not receive all the data, you should reposition the client. Remember, that even under ideal circumstances you cannot see an 802.11g client that receives traffic at 54 Mbps. You should expect about half the 802.11 data rate if data comes from a local source. Figure 12-4. Checking the Client's Performance
You can set up Chart view to display information from saved log files or you can display information in real time. The uses for the Chart view range from network performance spot checks to long-term analysis of data. The information bar below the graph provides the last, average, minimum, maximum, and duration data on the selected counter. When the information is captured to a log file, it is stored with the ability to read it later. Alert View
If you actively monitor your network, Chart view is an excellent tool. However, if you need another option, alert view is helpful. For example, you can set up Alerts to notify you when packet errors exceed a given threshold. If that threshold is breached, you can run a command-line executable. You can add alert counters the same way you do in the Chart view. The Alert view is located in the left pane of the MMC while the System Monitor snap-in runs. Right-click the Alert icon, and then select New Alert Settings from the context menu. A window pops up and asks for you to name the alert. For this example, the Alert is called Client Notification. The window looks like the one in Figure 12-5. Figure 12-5. Adding an Alert and Sampling Rate
The following are important aspects of this window, as marked in Figure 12-5: 1. Add a brief comment that describes the purpose of this alert.
2. View the counters that are monitored.
3. Click Add to add counters using the same method used for the Chart view. If you no longer want a counter monitored, click the Remove button.
4. Establish your threshold. The pull-down menu allows you to select either Over or Under. Next to it, you enter your chosen value. For this example, the value is set at 25.
5. These settings allow you to determine how often data is sampled. You can select a given amount of seconds, minutes, hours, or days to check the data. After you select the data to monitor, click on the Action tab. The result is shown in Figure 12-6. Figure 12-6. The Action Tab Is Used to Specify a Behavior to Process When an Alert Is Tripped
As Figure 12-6 shows, when the threshold is surpassed, you can select one or more of the following actions:
For Perfmon to send an alert message, it must be sent to a registered NetBIOS name, and the Alerter and Messenger services must run. In this example, the computer's Net Name is GOLDFINGER, so you do not have to establish a name. However, you can register a NetBIOS name at a specific computer if you enter net name Goldfinger/add at the Windows command prompt. After the name is registered, the alerts are displayed on that computer, which you can view by selecting the Schedule tab. Figure 12-7 illustrates the Schedule tab. Figure 12-7. Scheduling Start and End Times for a Performance Scan
To set up the time when the scan begins and ends, use the Schedule tab. You can start the scan at an exact time, and it can end either at an exact time, or after a certain period of time. Log View
You can collect your performance data at predetermined intervals for analysis later. The other views can then read the log file and perform their various functions as if the logged data were in real time. Each selected object is monitored, then the data written to the log. To start the view, right-click on the log in the leftmost pane of the MMC, then select New Log Settings from the context menu. Figure 12-8 shows the resulting window. Figure 12-8. Defining Which Network Performance Metrics to Log
By now you should understand how to add information to this log. The following explain the features of the General tab of the Log view, as numbered in Figure 12-8: 1. The file name of the current log.
2. A list of the counters that are logged.
3. Click Add or Remove to change counters and objects. The process is identical to the methods used Previously to add counters to the Chart and Alert views.
4. Use the Units drop-down list to establish how often data is sampled for the log. Note Be careful when you establish the time interval. Some objects can generate a huge amount of data for the log, and you might find yourself running out of hard drive space.
The Log Files tab, illustrated in Figure 12-9, helps you to manage some housekeeping attributes. Figure 12-9. The Log Files Tab Is Used for File Management
The list that follows describes the features of the tab, as numbered in Figure 12-9. 1. Determine what format you want to save the file. You can choose from binary, binary circular, text (both comma- and tab-delimited), or as a SQL database file.
2. The End file names with option is used to name your log files. You can end log files with a sequential number or with a timestamp and date stamp. The Schedule tab for Log view is similar to that shown for Alert view in Figure 12-6, and it is used to tell when to start and end the log. You can also tell Perfmon what to do when logging has ended; for example, it can start a new log file or application. Report View
The Report view displays the same counter information available from the Chart view; however, rather than showing performance data graphically, the information displays in a tabular format. Useful Perfmon counters for WLAN performance tuning come from the Network Interface performance object and include:
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