Direct Inward Dialing

The simplest dial plan possible within Lync Server 2010 is when each user in the organization has a direct DID number. DIDs are unique across the PSTN, and therefore unique within the Lync Server deployment. A PSTN caller or an internal user can use the same dial string to reach another user when DIDs are assigned to each user in the organization.

DIDs also typically map to a user’s internal extension. For example, at Company ABC’s San Francisco office, Alice has a DID of +1 (415) 777-3234, but internal users can simply dial 3234, the last four digits of her extension, to reach Alice. This gives the flexibility of numbers being unique across the site, but with the capability for PSTN callers to reach users directly. Internal users also have a short, four-digit dial string to remember in order to reach Alice.

On the Lync Server 2010 configuration side, Alice’s telephone URI field should be entered as tel:+14157773234 to uniquely identify her in the organization. A normalization rule within the San Francisco dial plan converts a four-digit extension starting with the number 3 into the full E.164 URI for users. That rule resembles the following:

Dial Plan: San Francisco

Name: Four-digit San Francisco extensions

Starting Digits: 3

Length: Exactly four digits

Digits to Remove: None

Digits to Add: +1415777

This rule handles the San Francisco DID range, but consider a scenario if Company ABC also has a Chicago office where users have DIDs starting with +1 (312) 444-5xxx. Because all the Chicago extensions start with a 5, any four-digit extension beginning with a 5 can be translated to include the Chicago DID prefix. Chicago users should have a telephone URI assigned resembling tel:+13124445xxx. A second normalization rule can be added to the dial plan to handle this office’s DID range:

Dial Plan: San Francisco

Name: Four-digit Chicago extensions

Starting Digits: 5

Length: Exactly four digits

Digits to Remove: None

Digits to Add: +1312444

After this rule is added to the dial plan, San Francisco users can dial by entering just four digits on a keypad or within the Lync client and correctly route to a user in either San Francisco or Chicago.