Measure wireless network performance using testing tool i. Perf. Many companies are upgrading their wireless networks to 8. By submitting your personal information, you agree that Tech. Target and its partners may contact you regarding relevant content, products and special offers. Here, we describe how to quantify network performance using i.

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Perf, a simple, readily- available tool that measures TCP/UDP throughput, loss, and delay. Getting startedi. Perf was developed to simplify TCP performance tuning by making it easy to measure maximum throughput and bandwidth.

When used with UDP, i. Perf can also measure datagram loss and delay (aka jitter). See this article to learn how to use i. Perf to measure throughput of wide area network (WAN) links. To use i. Perf, you must install two components: an i. Perf server (which listens for incoming test requests) and an i.

Perf client (which launches test sessions). A Win. 32 i. Perf installer can be found at NLANR, while a Java GUI version (JPerf) is available from Source. Forge. To measure Wi- Fi performance, you probably want to install i.

Perf on an Ethernet host upstream from the access point (AP) under test - - this will be your server. Next, install i. Perf on one or more Wi- Fi laptops - - these will be your clients. This is representative of a typical application flow between Wi- Fi client and wired server. If your goal is to measure AP performance, place your i.

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Perf server on the same LAN as the AP, connected by Fast or Gigabit Ethernet. If your goal is to isolate bottlenecks, co- locate your i. Perf server with real- world application servers, so that a comparable network path is traversed. Alternatively, i. Perf server and client can both be installed on Wi- Fi laptops.

This can be helpful to measure client- to- client performance if you plan to support streaming video or voice calls between wireless clients. Again, make sure that i. Perf traffic traverses the entire path you intend to test. For example, if you want to measure best case performance between co- located Wi- Fi clients, associate your i. Perf client and server to the same AP. If you want to see how routing through upstream switches or across a WAN impacts performance, associate your i.

Perf server to a central AP and let your i. Perf client associate with APs at various locations. Running i. Perf. By default, i. Perf clients establish a single TCP session to the i.

Perf server listening to Port 5. For example, start your i. Perf server by executing iperf - -s at the command prompt, then open another window to start your i.

Perf client: This just shows that you can measure throughput for traffic sent through the loopback address (1. If you cannot do this, you do not have i. Perf installed correctly. By default, i. Perf runs a 1. Mbps). Test length can be controlled by specifying time (- t seconds) or number of buffers (- n buffers). You can also view test results at regular intervals (- i seconds): To run many tests over a long period, you may prefer to run your i.

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Perf server as a daemon, writing server output to a log file. On Win. 32, this can be done by installing i. Perf as a service (i. Perf - -s - -D - -o logfile. When testing is finished, don't forget to remove the i. Perf service (i. Perf - -s - -R). If your test traffic will pass through a network firewall, make sure that port 5.

Perf to use a port that is already open (e. Perf - -c - -p 8. If your i. Perf server is behind a NAT firewall, you may need to configure a port- forward rule to reach it. Once the client can reach to the server, you can start measuring network performance.

Measuring TCP throughput. To determine max TCP throughput, i. Perf tries to send just data as quickly as it can from client to server. Default data is sent from an 8 KB buffer, using the operating system's default TCP window size. To mimic a specific TCP application, you can tell your i. Perf client to send data from a specified file (- F filename) or enter it interactively (- I).

For example: Unless you specify otherwise, the i. Perf client uses a single thread.

You can change this by requesting multiple parallel threads (- P number). When testing Wi- Fi, multiple threads on the same laptop may slightly increase total throughput: However, you'll need to use multiple laptops, each with its own Wi- Fi adapter, to simulate performance experienced by several discrete users. That's because multiple threads running on a single laptop are still sharing time on one Wi- Fi adapter.

On the other hand, if you have a laptop with more than one active adapter, you may wish to bind the i. Perf client to one adapter using its IP address (- B IPAddress). This is particularly important when using a multi- homed laptop simultaneously connected to Ethernet and Wi- Fi (or 3. G and Wi- Fi). i. Perf was originally developed to assist with TCP parameter tuning, but we won't delve into TCP window size and max segment size here because that's not our goal. However, when testing high- throughput APs, you may find it necessary to tune TCP parameters to get more out of each individual i.

Perf client - - to learn more, see Dr. TCP. Measuring UDP loss and delayi. Perf can also be used to measure UDP datagram throughput, loss, and delay. Unlike TCP tests, UDP tests do not send traffic as quickly as possible.

Instead, i. Perf tries to send 1 Mbps of traffic, packaged in 1. UDP datagrams (fits into one Ethernet frame). This rate can be increased by supplying a target bandwidth parameter, specified in Kbps or Mbps (- b #K or - -b #M). Here is an example: However, this just tells us only how quickly our i. Perf client was able to transmit. To learn more about UDP delivery, we really need to look at server- side results: Here, we can see throughput (measured over one second intervals), accompanied by loss (the number lost versus the number received) and delay (i.

The delay and loss that can be tolerated varies by application. For example, streaming video survives a good bit of delay by buffering input, while voice calls degrade quickly with delay. UDP tests can be refined by changing datagram buffer length, specified in Kbytes or MBytes (- l #K or #M). Unlike Ethernet frames with their 1. MTU (Maximum Transmission Unit), 8. In WLANs that use 8.

To. S is mapped onto Wi- Fi Multimedia (WMM) access categories. To learn more, see this tip on prioritizing Wi- Fi traffic. Looking both ways. In 8. 02. 1. 1a/b/g networks, over- the- air performance tends to be similar in both directions. For example, when distance causes data rate to drop or interference causes significant packet loss, both upstream and downstream application throughput are affected.

In 8. 02. 1. 1n networks, MIMO antennas and multiple spatial streams make this less true. Data frames sent from laptop to AP may (intentionally) take a completely different air path than frames sent from AP to laptop. As a result, it is now important to measure performance in both directions. Fortunately, this capability is built into i. Perf, controlled by two options: The - -d option tells your i. Perf server to immediately connect back to your i. Perf client at the port given by the - -L option for simultaneous tests in both directions.

The - -r option is similar, but tells your i. Perf server to wait until client tests are completed, alternating to repeat each test in the reverse direction. Finally, if you need to support multicast applications, try starting several i. Perf servers with - B to specify a multicast group IP address.

Then start your i. Perf client, connecting to that multicast group of i. Perf servers. Graphing resultsi. Perf programs can be run from the command line as shown in this tip, or launched from a Java front- end called JPerf. JPerf not only makes it easier to construct complicated command line parameters and save test results - - it also graphs those results in real- time. Figure 1. Using JPerf to launch i. Perf. Click on the image for a full size view.

Power. Shell commands in Windows Server 2. R2. Solutions provider takeaway: This chapter excerpt offers information on Power. Shell commands, uses, features, enhancements and command types in Windows Server 2. R2. Power. Shell can help solutions providers accomplish many tasks, including service and process management.

By submitting your personal information, you agree that Tech. Target and its partners may contact you regarding relevant content, products and special offers. You also agree that your personal information may be transferred and processed in the United States, and that you have read and agree to the Terms of Use and the Privacy Policy. Shells are a necessity in using operating systems. They give the ability to execute arbitrary commands as a user and the ability to traverse the file system. Anybody who has used a computer has dealt with a shell by either typing commands at a prompt or clicking an icon to start a word processing application. A shell is something that every user uses in some fashion.

It's inescapable in whatever form when working on a computer system. Until now, Windows users and administrators primarily have used the Windows Explorer or cmd command prompt (both shells) to interact with most versions of the Window operating systems. With Microsoft's release of Power. Shell, both a new shell and scripting language, the current standard for interacting with and managing Windows is rapidly changing.

This change became very evident with the release of Microsoft Exchange Server 2. Power. Shell as its management backbone, the addition of Power. Shell as a feature within Windows Server 2. Power. Shell as part of the Windows 7 and Windows Server 2. R2 operating systems.

In this chapter, we take a closer look at what shells are and how they have developed. Next, we review Microsoft's past attempts at providing an automation interface (WSH) and then introduce Power. Shell. From there, we step into understanding the Power. Shell features and how to use it to manage Windows 2. Finally, we review some best practices for using Power. Shell. Understanding Shells. A shell is an interface that enables users to interact with the operating system.

A shell isn't considered an application because of its inescapable nature, but it's the same as any other process running on a system. The difference between a shell and an application is that a shell's purpose is to enable users to run other applications. In some operating systems (such as UNIX, Linux, and VMS), the shell is a command- line interface (CLI); in other operating systems (such as Windows and Mac OS X), the shell is a graphical user interface (GUI). Both CLI and GUI shells have benefits and drawbacks. For example, most CLI shells allow powerful command chaining (using commands that feed their output into other commands for further processing; this is commonly referred to as the pipeline). GUI shells, however, require commands to be completely self- contained.

Furthermore, most GUI shells are easy to navigate, whereas CLI shells require a preexisting knowledge of the system to avoid attempting several commands to discern the location and direction to head in when completing an automation task. Therefore, choosing which shell to use depends on your comfort level and what's best suited to perform the task at hand. Note: Even though GUI shells exist, the term . Likewise, shell scripting refers to collecting commands normally entered on the command line or into an executable file. A Short History of Shells. The first shell in wide use was the Bourne shell, the standard user interface for the UNIX operating system; UNIX systems still require it for booting. This robust shell provided pipelines and conditional and recursive command execution.

It was developed by C programmers for C programmers. Oddly, however, despite being written by and for C programmers, the Bourne shell didn't have a C- like coding style. This lack of similarity to the C language drove the invention of the C shell, which introduced more C- like programming structures.

While the C shell inventors were building a better mousetrap, they decided to add command- line editing and command aliasing (defining command shortcuts), which eased the bane of every UNIX user's existence: typing. The less a UNIX user has to type to get results, the better. Although most UNIX users liked the C shell, learning a completely new shell was a challenge for some.

So, the Korn shell was invented, which added a number of the C shell features to the Bourne shell. Because the Korn shell is a commercially licensed product, the open source software movement needed a shell for Linux and Free. BSD. The collaborative result was the Bourne Again shell, or Bash, invented by the Free Software Foundation. Throughout the evolution of UNIX and the birth of Linux and Free.

BSD, other operating systems were introduced along with their own shells. Digital Equipment Corporation (DEC) introduced Virtual Memory System (VMS) to compete with UNIX on its VAX systems. VMS had a shell called Digital Command Language (DCL) with a verbose syntax, unlike that of its UNIX counterparts. Also, unlike its UNIX counterparts, it wasn't case sensitive, nor did it provide pipelines. Somewhere along the way, the PC was born. IBM took the PC to the business market, and Apple rebranded roughly the same hardware technology and focused on consumers. Microsoft made DOS run on the IBM PC, acting as both kernel and shell and including some features of other shells.

Windows introduced a GUI shell, which has become the basis for Microsoft shells ever since. Unfortunately, GUI shells are notoriously difficult to script, so Windows provided a DOSShell- like environment. It was improved with a new executable, cmd. Regrettably, this change also meant that shell scripts in Windows had to be written in the DOSShell syntax for collecting and executing command groupings. Over time, Microsoft realized its folly and decided systems administrators should have better ways to manage Windows systems. Windows Script Host (WSH) was introduced in Windows 9.

Windows. It was a library that allowed scripting languages to use Windows in a powerful and efficient manner. WSH is not its own language, however, so a WSH- compliant scripting language was required to take advantage of it, such as JScript, VBScript, Perl, Python, Kixstart, or Object REXX. Some of these languages are quite powerful in performing complex processing, so WSH seemed like a blessing to Windows systems administrators.

However, the rejoicing was short- lived because there was no guarantee that the WSHcompliant scripting language you chose would be readily available or a viable option for everyone. The lack of a standard language and environment for writing scripts made it difficult for users and administrators to incorporate automation by using WSH. The only way to be sure the scripting language or WSH version would be compatible on the system being managed was to use a native scripting language, which meant using DOSShell and enduring the problems that accompanied it. In addition, WSH opened a large attack vector for malicious code to run on Windows systems. This vulnerability gave rise to a stream of viruses, worms, and other malicious programs that have wreaked havoc on computer systems, thanks to WSH's focus on automation without user intervention. The end result was that systems administrators viewed WSH as both a blessing and a curse. Although WSH presented a good object model and access to a number of automation interfaces, it wasn't a shell.

It required using Wscript. Cscript. exe, scripts had to be written in a compatible scripting language, and its attack vulnerabilities posed a security challenge.

Clearly, a different approach was needed for systems management; over time, Microsoft reached the same conclusion. Introduction to Power. Shell. The introduction of WSH as a standard in the Windows operating system offered a robust alternative to DOSShell scripting.