Dialable numbers are created by analyzing a given number and finding a number modification rule that applies to the presenter of the number (from) and the receiver of the number (to).

**Note: **
In a basic call scenario, Lotus Sametime Unified Voice creates 3 dialable numbers:

- The Calling Party Number presented by the calling party (from) to the called party (to)

- The Alerting Party Number presented by Lotus Sametime Unified Telephony on behalf of the called party (from) to the calling party (to) with presented number the result of translation

- The Connected Party Number presented by the called party (from) to the calling party (to)

## Requirements

To be able to create a dialable number, the number modification library needs to know

**What is the Number that needs to be made dialable? **

This number could be the number of a Lotus Sametime Unified Telephony subscriber or could be a number received on the network interface.

**Who offered the number for presentation? **

In case the number was obtained from a Lotus Sametime Unified Telephony subscriber, it was this subscriber who offered the number. In case the number was received on the network interface, the endpoint (gateway, media server, etc.) that sent the number is the one who offered the number. Instead of the subscriber or endpoint, the number modification library expects the numbering plan used by the subscriber or endpoint.

**For whom does a dialable number need to be created? **.

In case the dialable number is requested for a Lotus Sametime Unified Telephony subscriber, it is this subscriber.

In case the dialable number is requested for an endpoint (media server, etc.) or a private or public network (gateway) it is the endpoint.

**What is the number of the party that wants to receive a dialable number?**

This can be a Lotus Sametime Unified Telephony subscriber's number or in case the dialable number is created for an endpoint it is the endpoint's configured default Home DN or if that's not configured it is the called party number

In order not to overload the tables that contain the rules on how a number between 2 subscribers or between a subscriber and an endpoint or between 2 endpoints is shown, most table's granularity is constrained to the Private Numbering Plans used by the subscribers or endpoints.

**Note: **
This means that all Lotus Sametime Unified Telephony subscribers that use a particular Private Numbering Plan will receive the same treatment from Display Number Modification. It is however possible to create a number modification rule that applies to a specific endpoint.

**Figure 1. Creating a dialable number using the Number Modification Library**
## Functional Sequence

There are multiple steps to creating a dialable number and it is very important that a Display Number Modification Library administrator understands the different steps/phases that a presentation number passes through to become a dialable number. Factors taken into consideration by Lotus Sametime Unified Telephony are:

Is the presenter of the number a SIP Subscriber or an endpoint (SIP or SIP-Q)?

Is the call between the 2 parties an internal or an external call?

This results in 4 basic scenarios:

- Internal Call where presenter is a SIP subscriber: The number to be presented (input number) is in order of preference:

- The subscriber's main pilot directory number if configured to use the main pilot directory number as identity for internal calls.

- The subscriber's directory number.

- External Call where presenter is a SIP subscriber and receiver is a SIP subscriber: The number to be presented (input number) is in order of preference:

- The subscriber's external Caller ID.

- The subscriber's main pilot directory number if configured to use the main pilot directory number as identity for external calls.

- The subscriber's directory number if it is a public number.

- The subscriber's business group's display number.

- External Call where presenter is a SIP subscriber and receiver is an endpoint (SIP or SIP-Q): The number to be presented (input number) is in order of preference:

- The subscriber's external Caller ID.

- The subscriber's main pilot directory number if configured to use the main pilot directory number as identity for external calls.

- The subscriber's directory number if it is a public number.

- The receiver's Default Home Directory Number.

- The subscriber's business group's display number.

- For a call where the presenter is an endpoint (SIP or SIP-Q) The number to be presented (input number) is in order of preference:

- The normalized form of the number received from the endpoint (calling party number, connected party number, etc) or the normalized form of the translation result (called party number)

- The number received from the endpoint (calling party number, connected party number, etc) or the translation result (called party number)

To get the dialable number for any of the above determined numbers, the Number Modification Library does as follows:

In a first step the presented number is evaluated to determine the type of the number.

Once the type of number is determined, the best matching Modifications table entry is searched in the Display Number Modification library based on the presenting (from) and the receiving (to) party's context information.

When found, the modification rule of the entry determines what happens next.

If the found modification rule fails, Lotus Sametime Unified Telephony will keep searching for a match in lower priority Modifications table entries that still match the presenting (from) and receiving (to) party's context information.

## Determining the Type Of Number

The general flow for determining the Type of Number for a number for an endpoint is as follows:

Unless the Type of Number is already determined to be International or L2, the number normalization table is consulted to find out whether normalization entries apply that may upgrade the number to a fully qualified number. If successful, the normalized number and its Type of Number (International, L2 L1 or L0) is determined.

If the resulting Type of Number remains Unknown (no entry matches in the number normalization table), the number prefix table is used to check if the type of number can be determined from the leading digits of the input number. If successful, the leading digits are stripped from the number and the Type of Number is determined.

If the resulting Type of Number is still Unknown (no entry matches in the number prefixes table) then a lookup is done - mostly for backward compatibility reasons - in the number definition table to see whether a match there could resolve the Type of Number.

**Note: **

The result of getting the type of number of a number presented by an endpoint not only determines the Type of the presented Number, it also may change the number to its normalized format.

**Figure 2. Determining the Type of Number for a Number from an endpoint**
The general flow for determining the Type of Number for a number of a subscriber (Home DN) is as follows:

If the Type of Number is Unknown, a lookup is done in the number definition table to see whether a match there could resolve the Type of Number

**Figure 3. Determining the Type of Number for a SIP subscriber**
Because of the above, it is strongly recommended to enter the number definitions for all office codes used in the Lotus Sametime Unified Telephony. Normally, system-wide number definitions can be entered for each public office code and business group specific number definitions can be entered for each private office code. In case of hosted scenarios, public office codes (if shared among multiple business groups) may result in business group specific number definitions as well.

## Criteria for Finding a Matching Number Modification Entry

To find a match in the Modifications table of the Display Number Modification library, the context of the number presenter (from) and number receiver (to) and the determined type of number of the presented number are matched against the entries in the Modifications library.

To guarantee a consistent result the entries in the Modifications table are ordered. The following factors determine the priority with which an entry in the number modifications table is looked at (from highest to lowest):

Rules where the receiver (to) is a specific endpoint.

Rules where the receiver (to) is a private networking endpoint (SIP or SIP-Q) (ALL-PN).

Rules where the receiver (to) is an endpoint (ALL).

Within each of these 4 categories, the following priorities are assigned to the receiver's group membership:

Rules where the receiver (to) uses a specific numbering plan.

Rules where the receiver (to) belongs to a specific business group (ANY numbering plan).

Rules where no business group is specified for the receiver (to) (ANY numbering plan of ANY business group).

Within each of these 3 subcategories, the following priorities are assigned to the presenter's group membership:

Rules where the presenter (from) uses a specific numbering plan.

Rules where the presenter (from) belongs to a specific business group (ANY numbering plan)

Rules where no business group is specified for the presenter (from) (ANY numbering plan of ANY business group)

Within each of these 3 subcategories, the following priorities are assigned to the type of number of the presented number (input TON):

Rules where the input TON is defined (International, National, Subscriber, L2, L1 or L0).

Rules where the input TON is not defined (ANY)

And finally, within each of these 2 subcategories, the priorities of the Modifications table entry are taken into account (1 - 4).

**Note: **
The Telephony Control Server Assistant will display the Number Modification rules in the above order when entering the Number Modifications overview screen.

**Parent topic: **Display Number Modification