Application Service Provider
Where an Internet Service Provider (ISP) offers Internet connectivity, such as from an end user to a web server, an Application Service Provider offers connectivity to the web pages themselves. ASPs also may be "hosting providers", providing high-availability, well-connected data centers into which enterprises may install their servers, yet have someone else do the day-to-day administration. ASPs also frequently offer high-availability services ranging from managed backups to hot standby servers.
ISP and ASP roles are not mutually exclusive. Many ISPs offer web service, in which the customer pays for storage, processing, and bandwidth. If users cannot connect to the server at all, the Internet services part of the organization deals with their problem, but if the web page is corrupted or is giving poor performance, the application support group deals with that issue.
ASPs can offer connectivity not only to users from the Internet, but to intranets and extranets implemened as Virtual Private Networks (VPN). When compared to a pure ISP, an ASP can offer backup and disaster recovery for the application itself, including moving it to an geographically remote data center. Indeed, for critical applications, an ASP can run the master copy, but "shadow" it with a backup server, in another location, that can immediately take over a failing application or even transaction. This kind of failover is made easier with the wide range of virtualization technologies on hosts.
Content distribution networks and application acceleration providers are not necessarily pure ASPs, although they complement them, and ASPs may have their own services of this type. In a content distribution network, for example, web content exists on a master server, but the CDN copies it to a large number of servers physically at local ISPs. When the end user asks for a web page, the intelligent Domain Name Service (DNS) server of the CDN will return the address of the closest available server with a copy of the page, reducing the delay in reaching it. If the application is written in Java, an application acceleration service can direct the user to the nearest server with an appropriate Java Virtual Machine.
Some ASPs specialize in certain industries, and are intimately familiar with security and regulatory requirements of that industry. For example, in the U.S., an ASP focused on the healthcare industry will know how to comply with all the nuances of the Health Insurance Portability and Accessibility Act (HIPAA), which specifies privacy rules for personal health information. Another ASP might have special competence in acting as a hot standby data center to financial institutions.