A captive portal is a Web page that the user of a public-access network is obliged to view and interact with before access is granted. Captive portals are typically used by business centers, airports, hotel lobbies, coffee shops, and other venues that offer free Wi-Fi hot spots for Internet users.
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When a potential user first logs on to a network with a captive portal, a Web page is encountered that requires certain actions before Internet access is granted. A simple captive portal forces the user to at least look at (if not read) an acceptable use policy (AUP) page, and then click on a button indicating agreement to the terms of the policy. Presumably, this can help absolve the provider from liability in the event the user commits criminal or other destructive activity while logged on. In some captive portals, advertisements for the provider's sponsors are displayed, and the user must click through them or close the windows in which they appear before accessing the Internet. Some captive portals require the entry of a pre-assigned user ID and password before accessing the Internet. Such authentication may discourage the use of wireless hot spots as sites for carrying on criminal activities. Most servers with captive portals include anti-virus and firewall programs to help protect users' computers from the Internet and from each other.
Even when a simple captive portal is used in a free public-access network, certain people may repeatedly connect, using the network on an almost continuous basis to download music, videos, or other large files. This activity, called bandwidth hogging, can be minimized by additional programming in the captive portal. Such programming can control the speed at which large files are downloaded, limit the size (in kilobytes or megabytes) of files that can be downloaded, restrict the number of downloads that can occur in a single session, or block connection to Web sites commonly used for downloading large files. This is called bandwidth throttling or traffic shaping.