PSTN vs ISDN: Which Business Landline is Right for You?

Many businesses just assume that a landline is a landline … until they go to sign up for one.

Regular business landlines come in two flavours: PSTN and ISDN. (We’ll leave VoIP to one side for now, and talk about that another day.)

Both systems have their pros and cons, and the ideal solution for your business may well be to use a combination of the two.

PSTN (Public Switched Telephone Network)

PSTN, which is also called POTS (Plain Old Telephone System), supplies a single phone line with a single phone number.

This service is ideal for smaller businesses that require only one or two lines. It is also recommended for many services where a dedicated line is required, such as fax and EFTPOS machines, back-to-base alarm systems, and ADSL connections.

ISDN (Integrated Services Digital Network)

The ISDN digital service provides multiple channels per line, and enables multiple concurrent phone calls. Each digital line can carry both voice and data services. These lines provide greater bandwidth than PSTN lines, which makes them well suited for services including data transfer and video conferencing.

This service is ideal for medium to large businesses, and is typically connected to office phones through a PBX system.

For most businesses, only 30-40% of their phone lines are in use at any one time. That means that in an office with 10 staff where everyone has their own phone, you would require either 10 PSTN lines or 4 ISDN lines. This helps to make ISDN cost effective, especially in larger offices.

  • ISDN 2
    This is the starter level for ISDN, providing two channels on your ISDN line. As your business grows, this service can be expanded to 4, 6, and then 8 channels.
  • ISDN 10, 20, 30
    Larger businesses can sign up for 10, 20 or 30 ISDN channels. Services are easily upgraded from 10 to 20 to 30. If you require more than 30 channels, a second ISDN service can be installed.

With ISDN, each phone within your business can have a unique phone number, which people from outside the business can dial directly. (This is called a DID or Direct In-Dial number.) You can typically purchase DID numbers in blocks of 100 from your telco. When you purchase a block of numbers in this way, they remain yours, and you can take them with you if you ever decide to change to a different carrier.

Which one is right for your business?

For medium to large business, an ISDN system for your phone lines will help to save you money (remembering that you need 60-70% fewer lines than for a comparable PSTN system).

Before you go all the way with ISDN, it’s important to look at the dedicated services that you want to run. For example, services such as ADSL and some back-to-base alarm systems are incompatible with ISDN. (If you’re not sure what types of lines your services are compatible with, it’s a good idea to check with your suppliers.)

So the best solution for many medium to large businesses is to use ISDN for their phone lines, plus get a few PSTN lines for stand-alone services.

Smaller businesses will often be paying about the same for an ISDN solution as they will for a PSTN solution. The main consideration here is the future growth expected for the business. The more phone lines you need, the more cost-effective ISDN becomes, so if it’s likely the business will grow rapidly, it will probably be more cost effective to start with an ISDN 2 system.

Alltel supplies both PSTN and ISDN landlines for businesses, so please give us a call on 1300 ALLTEL (255 835) if you need any help deciding which type of line is best suited for your business.