The Centrex model

The second model is the  central office exchange service, or Centrex, model. Centrex is physically set  up the  same as the  POTS access line model. Like POTS, Centrex uses the  same physical twisted-pair copper lines.

The difference between the  POTS and  Centrex models lies in how the  line is terminated at the  carrier company’s facility. Instead of getting switched into the  PSTN directly, the  Centrex line first goes  to the  more  intelligent main- frame-level telephone system owned and  operated by the  carrier. From there, the  system can provide the  customer with many  more features not  directly available on a plain  POTS line. To get these features on a POTS line, the  cus- tomer typically has  to pay for each feature. Centrex provides a bundle of features with little or no added charges.

Because you get more  with Centrex, you pay a little more  for the  line on a
per-line  per-month basis. Centrex is a good  alternative for companies operat- ing out  of temporary facilities (such as a lease situation) and  for companies that can’t or don’t  want  to maintain a full-blown telecommunications infra- structure. When you lease a Centrex system, maintenance is usually included, which reduces the  need for skilled  staff on the  company payroll.

The good  news  is that a VoIP solution exists for the  more  traditional Centrex situation: VoIP Centrex. You need a computer network in the temporary premises, but  that is an expense you can unplug and  take  with you when  you move  to your  permanent location. With VoIP Centrex, you can start your  VoIP network, acquire features galore, and  get the maintenance services you need. When you move  to your  new, permanent location, you simply  plug in your  network, and  you are up and  running.

With any Centrex option, you pay more  per  month in return for avoiding the  need to sink costs into your  own infrastructure. Also, by using  the Centrex host’s facilities, you get a rich  feature set  with no additional monthly charges. Another benefit is that you can walk away from a Centrex solution anytime you want  without penalty. Although some smaller companies keep  Centrex forever, most growing  companies eventually convert to one of the  models described in the  following section.