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Dictionary of Load Testing Terms


Business Case – An interaction the user has with the web-based application or website that has meaning in a business context. It could be as simple as viewing a single page, or as complicated as performing an entire transaction. In Web Performance Load Tester™, this represents a series of HTTP Transactions that should be repeated by virtual users during a test. More generically known as a test case.

Cache – The web browser maintains a copy of recently requested resources (pages, images etc.) so that when the resource is needed again, it does not have to ask the server for another copy. This greatly improves the performance of the browser - especially on a graphics-laden website where images (menu bars, for instance) are reused on multiple pages.

Controller – Web Performance Load Tester™ can be run in two modes - as the controller or as an engine. In controller mode, Web Performance Load Tester™ presents a GUI that allows the recording, editing and execution of load tests. Only one controller may be run on a network with the same license key.

Delay Time – The amount of time between receipt of one URL and the request of the next URL. Web Performance Load Tester™ records this duration while recording a business case and uses it to accurately simulate a users behavior when performing a test. When a delay time occurs between a web page and the first image (URL) on the web page or between two images on a web page, the delay time is usually due to the processing time required by the browser to parse the page and render it (and the images) on the screen. When the delay time occurs after the final image in a web page and the next web page, the delay time represents the time spent by the user reading the page and deciding what to do next. In this case, the delay time is referred to as Think Time.

Engine – Web Performance Load Tester™ can be run in two modes - as the controller or as an engine. In engine mode, Web Performance Load Tester™ presents a console interface and listens for commands from a controller. It is used by the controller for generating virtual users. Many engines can be used by a controller to generate massive network loads.

FTP (File Transfer Protocol) - A network protocol for sending and receiving files. FTP is built on top of TCP/IP.

HTTP (Hypertext Transfer Protocol) - The protocol used between web browsers and web servers to transfer web pages and associated files (images, etc). It is the language of the World Wide Web. HTTP is built on top of TCP/IP.

HTTP Transaction – A request sent from the browser to the server and the corresponding response from the server to the browser, both sent using HTTP. This round-trip communication path allows the browser to request a resource (URL) and receive a response from the server. It may include content sent by the browser (data entered in form fields, uploaded files) and content returned from the server (web page, image, etc).

host – A computer that is connected to a TCP/IP network, including the Internet. Each host has a unique IP address.

IP (Internet Protocol) - A network protocol that specifies the format of data transferred between two hosts (called packets or datagrams) and the addressing scheme. IP by itself is something like the postal system. It allows you to address a package and drop it in the system, but there is no direct link between you and the recipient. IP is generally used in conjunction with TCP.

IP address – An identifier used by the IP protocol to identify an individual host. The current version of IP, IPv4 uses 4 numbers to identify each network address. Each number can be in the range of 0-255. For example, 161.58.192.211 is the IP address of the Web Performance, Inc. web server. Note that certain IP addresses have special meanings. 127.0.0.1 is the 'loopback' address that a host uses to redirect traffic to itself (usually for diagnostic purposes). The address ranges 10.*.*.* and 192.168.*.* are always reserved for internal networks. 127.*.*.*, 0.*.*.* and 255.255.255.255 are also reserved for special uses.

License key – An encrypted file that contains the critical license information for your installation of Web Performance Load Tester™.

multihome – An adjective used to describe a host that is connected to two or more networks or has two or more network addresses. For example, a network server have multiple network interfaces to increase maximum throughput.

Proxy Server – A server, typically on a private network, that allows access to external network resources. In a common network configuration, the computers on a company network are separated from the Internet by a firewall (for security reasons). Since these computers cannot access the Internet directly to browse web pages, the browser must be configured to use a proxy server (which is allowed to access the Internet) to service requests for web pages from the Internet. All common browsers support this configuration, usually in a configuration section titled "Use a Proxy Server".

Real Browser– An actual browser, exactly the same as a user would used, such as Google Chrome.

Sample Period – A time period during a load test during which data is aggregated. The statistics calculated by Web Performance Load Tester™ are calculated for each sample period during the test.

Session TrackingHTTP is 'stateless'. This means that between the time your browser receives a web page and asks for the next page, the server has forgotten who you are - in other words, when your browser asks for the second page, it has no way to know that it was the same browser that asked for the first page. This is obviously a problem for any application that needs to remember who you are - such as an application that requires a login. The notion of a single, unique user browsing from one page to another is referred to as a 'session'. As the web has evolved, several techniques for session tracking have evolved. The most common are cookies and URL-rewriting.

SMTP (Simple Mail Transfer Protocol) - A network protocol for transferring e-mail messages between servers. Most e-mail systems that send mail over the Internet use SMTP. SMTP is built on top of TCP/IP.

Test case - See business case.

TCP (Transmission Control Protocol) - A network protocol that enables two hosts to establish a connection and exchange streams of data. TCP guarantees delivery of data and also guarantees that packets will be delivered in the same order in which they were sent. TCP is a little like a phone call - there is an extended connection between two hosts during which either host can send data to the other.

TCP/IP – the suite of communications protocols used to connect hosts on the Internet. TCP/IP uses combines the TCP and IP protocols to provide addressing and reliable data transfer for a variety of other Internet protocols, including HTTP, FTP and SMTP.

Think Time – The time between the browser displaying a page to the user and the user clicking a link to browse to the next page. This time could be the time it takes the user to read the content of the page or decide what to do next. Web Performance Load Tester™ records this time when recording a Business Case and uses it to accurately simulate the users when performing a test. See also Delay Time

TTFB – TTFB stands for "Time to First Byte" and is the duration between the time the virtual user made an HTTP request, and the time the first byte of the response from the web server arrived. This value gives an idea of the responsiveness of the network and web server, and consists of the socket connection time, the time to send the HTTP request, and the time to receive the first byte of the HTTP response.

URL (Uniform Resource Locator) - A specially formatted string that describes a resource on the Internet. This is used by the browser to determine where on the network the resource is located. A typical URL looks like this: http://www.webperformance.com/library/dictionary.html

Virtual Browser –A simulated browser that simulates everything about a real browser, including the number of simultaneous socket connections and caching behavior. In order to efficiently generate thousands of users per machine, however, it does not actually render web page content.

Virtual User – A software entity, internal to Web Performance Load Tester™, that simulates a real user by repeatedly performing a Business Case during a load test.

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