Uniform Resource Identifier

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While many are familiar with URLs, we see them every day and use them to navigate the WWW, there exists another entity that takes the concept of a URL and expands on its capabilities. This is called the universal resource identifier (URI). The URI is a generic identifier that describes an end point for communications. The most common use of URIs today is in the VoIP environment where the session initiation protocol, SIP uses a URI to identify a communication resource.

The SIP URI is similar to an email address, and typically contains a user-name and a fully qualified domain name. An example would be SIP:peter@hill.com. SIP also supports a secure URI, called a SIPS URI, where call setup messages are encrypted using transport layer security.

The difference between a simple URL and a SIP URI is the set of options that can be added to the SIP URI. In addition to the name and domain the SIP URI can contain passwords, protocols to use in the session, the priority of the session, a subject line, a cause code (for redirected traffic), a target code, say a voice mail box, a device type (phone vs. PC), a day/date stamp. All these additions allow SIP to create special sessions based on the wishes of the participants.

Imagine the concept of requiring a password to all incoming calls, You could accomplish this by adding your password to all outgoing calls and have it automatically added to return calls. In this case the password would be unknown to others (namely telemarketers). Another capability would be to program your phone to add a high priority indicator to calls to your children; I suppose that might drive them crazy. The target and cause optional elements can be used by voice mail systems to accurately deliver calls to the proper message. Calls that are redirected based on busy, vs. blocked vs. no answer can be identified and sent to the different messages. The combination of voice over the Internet, the addition of telephone numbers to the Internet’s DNS and the optional capabilities of the URIs are truly changing what is considered plain old telephone service.

The URI can have many forms; several examples are listed below.

PodSnacks

<mp3>http://podcast.hill-vt.com/podsnacks/2007q3/uri.mp3%7Cdownload</mp3> | Uniform Resource Identifier (URI)