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  CommServ > Reference > Background > PBX vs. Centrex: CalPoly San Luis Obispo

PBX vs. Centrex: CalPoly San Luis Obispo

The following is text extracted from handouts distributed at a presentation made by CalPoly of San Luis Obispo representatives to the members of the UCSB Telephone Advisory Committee on December 1, 1995. The topic of the presentation was a comparison between Centrex telephone service and a campus-owned PBX (Private Branch eXchange) telephone switch.


  • They've been using a PacBell Centrex system on campus for many years (over a decade).
  • When they first starting using Centrex, they received excellent service from PacBell. However, they feel that service had degraded somewhat over the past two years, primarily because PacBell (like all other local exchange carriers) has been reducing their work force and consolidating staff into a fewer number of cities. Their service now comes from an office in Sacramento.
  • They have approximately 300 ISDN circuits installed on campus, but only one was installed correctly. All others had to be modified (re-configured) after installation.
  • They're using ISDN circuits only for voice communications, not for data communications (because they have an extensive data network on campus). They're using ISDN voice to provide software features and provide multi-line telephone systems, instead of using the old analog multi-line instruments.
  • They're evaluating converting from a PacBell Centrex system to a PBX in late 1997 when their current contract expires.

Strengths & Weaknesses

Centrex Strengths

  • PacBell can provide an essentially unlimited number of technicians for installations and repairs.
  • The switch traffic is controlled for the customer. The customer doesn't have to manage the switch and its software. Most recent upgrades are installed automatically with no additional cost for service.
  • A large clientele base permits wider experience in troubleshooting and service issues.
  • Twenty-four hours per day repair service is available at no change (above the monthly rental for the telelphone line) when service is down.
  • New area codes and prefixes are automatically loaded in the switch software.

Centrex Weaknesses

  • The University is not in control of the switch.
  • Technicians are not always familiar with campus locations and/or procedures
  • Since the University does not have control over the switch, software changes are sometimes made without notification and the changes affect special functions utilized on the campus.
  • Technicians may make unwanted changes, and the University has to pay to have the changes reversed.
  • Orders placed for service flow through multiple PacBell departments prior to implementation. It makes it difficult to locate and correct errors when your service does not work correctly.
  • When repairs are necessary, the University cannot readily determine whether the problem is within the CPU or the switch. If the (PacBell) repair group is busy, you must make additional calls to escalate your problem.
  • It is costly to route long distance traffic to multiple vendors (Interexchange Carriers) since the University must pay for hardware at the Centrex switch.
  • Global changes to lines either have to done manually by you (the customer) or the changes take days.
  • (PacBell's) On-line service ordering system does not integrate with (University's) telemanagement systems. If you do not use the on-line order system, installation costs (from PacBell) are higher.




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