Matrix PRASAR UCS - Direct Dialing-In (DDI)

Matrix PRASAR UCS System Manual 803
Direct Dialing-In (DDI)
What’s this?
DDI is the service feature provided to the customers by the ITSPs over SIP Trunks. DDIs are Direct Dial-In
numbers. These are additional numbers that can be associated with the main number assigned to the SIP Trunk.
They are normally used with the system to provide separate numbers to extension users.
When there is an incoming call on the a specific DDI number it is routed through to the required extension without
operator intervention.
Before we understand how DDI routing works, we must understand the following terms:
• Pilot Number/ISDN Number: It is a single number assigned by the service provider to a single SIP trunk.
This is the combination of MSN Number and the first DDI Number. The Pilot Number is of maximum 16
digits. This is also known as ISDN Installation Number/ISDN Number. The MSN is a fixed series and is
given by the service provider whereas the DDI Numbers can be selected by the user and these series
vary. For example, if the Pilot Number is 2630555, the MSN is 2630 and the DDI Number is 555. However
the number of digits to be used as DDI Numbers is informed by the service provider as they may differ for
each service provider.
• Multiple Subscriber Number (MSN): In India, the MSN are the first four digits of the Pilot Number, which
remain fixed and are provided by the service provider. The number of fixed digits may vary depending on
the service provider.
• DDI Numbers: These are additional numbers, which can be selected by you but are allotted by the service
provider. These are sequential numbers. In the DDI number only the last 3 or 4 digits vary. These are
known a DDI numbers. However the number of DDI digits which vary are provided by the service
provider. These numbers are normally used with a PBX and are assigned to the extension user.
How it works
Let us understand this with the help of an example:
• A SIP Trunk has been connected to the PBX.
• 50 DDI numbers have been given by the service provider.
• Incoming calls on the DDI numbers can be routed to different landing destinations as extension users,
department groups or other trunks within the organization.
• To assign DDI numbers to the extension users and to route calls as per the DDI numbers, you need to
configure the following:
• Incoming Reference Table
• Outgoing Reference Table
• DDI Routing Table