Site Prefixes

A common scenario with an organization spread across multiple sites is that extensions are not unique within the organization. Typically, a PBX exists in each site and the same extensions are used across sites. When this occurs, either users can use a full DID to reach users in another site, or a site prefix or steering code might be assigned.

For example, consider a scenario in which Company ABC has offices in San Francisco and Chicago. Alice and Bob both work in the San Francisco office, where Alice has extension 234 and Bob has extension 456. When Bob wants to dial Alice, he can simply dial 234 and be connected immediately. Now assume that Joe works in the Chicago office where a different PBX exists, and also with extension 234. Bob cannot simply dial Joe using 234 because he will connect to Alice instead.

What happens as a workaround is that a site prefix code can be assigned to Bob’s dial plan so that he can dial Chicago extensions by prepending an extra digit. In this scenario, assume that 6 is the site prefix for Chicago from San Francisco. This means Bob can dial 6, followed 234, and be connected to Joe, but still dial 234 to reach Alice directly.

The same kind of site prefix is used in this scenario for Chicago users to dial San Francisco users directly. In Company ABC’s case, Chicago users can use 7 as a prefix to dial San Francisco. Although Joe and Alice have the same three-digit extension, Joe can contact Alice by dialing 7, followed by 234.

Site prefixes can be potentially confusing for end users because they must remember to dial extra digits for different sites. Often, they have to consult a list of site prefixes or look up a contact phone number when dialing a different location.

Keep in mind that as organizations shift to Lync for voice, the use of site prefixes is reduced because most of the dialing can be done with a simple click on a contact. Unlike with traditional telephony, users will become more and more reliant on click-to-dial features, instead of remembering extensions. Despite the ease of the user experience, administrators will still be tasked with correctly assigning site prefixes to telephone URIs and creating appropriate normalization rules. This can become a complex voice-routing and dial-plan configuration in the end.