Take a moment to consider how much telephone systems have evolved since the original patent was awarded to Alexander Graham Bell in 1876. At that time long-distance phone calls were not even possible. Now, thanks to innovative technological innovations, telephone system capabilities are seemingly endless. However, while these impressive changes have been beneficial, many small and medium sized business owners have been left uninformed. This creates quite the problem when purchasing telephone services and making installation decisions.
One feature offered by telephone companies for use with customers' business telephone system is direct inward dialing (DID). DID provides outside callers with the ability to dial a PBX extension without going through a receptionist or auto-attendant. DID services differ from regular analog trunk lines (POTS lines) in a few respects. First, analog trunk lines allow incoming and outgoing calls. DID services only allow incoming calls. Second, each analog trunk line has it's own phone number and requires it's own circuit. DID services have less circuits than phone numbers. Essentially, DID services provide businesses a less expensive way to give multiple employees their own phone number.
In DID service, the telephone company provides the customer with one or more trunk lines and assigns a range of telephone numbers to these lines. For instance, a typical ratio would be to order 20 DID phone numbers with 5 DID trunk lines. This makes it much cheaper to give multiple employees their own direct phone numbers. You're only paying for 5 trunk lines and getting 20 phone numbers.
When a customer dials a DID phone number, an unused DID trunk line is located, so the call can be connected. The phone company also passes the last three digits of the DID phone number to your phone system for call processing. A phone call to 123-1112 would pass the digits 112, and your phone system would be programmed to use these digits to forward the call to a particular phone extension. 123-1112 could go to extension 10, while 123-1113 could go to extension 11 and so on. In this scenario, employees could give out their direct inward dial number to customers and even have it printed on their business card. There would be no need for a customer to call in and ask to be transferred to an extension. They could simply dial a DID phone number to contact their party.
DID lines can also be used by fax servers. In this case, a phone line is run into a computer that runs fax server software and fax modem cards. Just as with PBX extensions, a set of digits of the assigned phone numbers are used to identify the unique fax recipient. This allows the business to assign distinct fax numbers to many individuals while only running one fax machine.
If you are a small to medium sized company that does not want to use an auto-attendant or hire someone to act solely as an operator, analog direct inward dial lines would be a great choice. Direct inward dialing is also a great way to separate general sales and service calls from known customers that call particular agents often.
By Bob Hunter