Upgrading Centrex to IP-PBX

["Aaron Solomon using FreeBSD 6.2" <>]

Dear All,

This is Quincy @ TANet (Taiwan Academic Network). 
We would like to consult experts in Internet2 about the experience for
migrating a Centrex system to IP-PBX.
Because no university in Taiwan has done this in a campus-wide scale,
we are looking for reference sites abroad. 
If any member in Internet2 has experience on integrating
Centrex system with VoIP, we appreciate if you would like to share
your experience.

The following is the description of my question:

National Taiwan University (NTU) is now leasing Centrex service (10,000
phone numbers) from Chung-Hwa Telecom, the largest telecommunication
company in Taiwan. NTU owns the copper links inside the campus.

The phone numbers in use are approximately 8,000, in which 5,000 are
assigned to departments in university, and 3,000 are for students
dormitories. New buildings are under construction, so they are planning
to extend the telephony system. NTU plans to build a new IP-PBX system.
Their tentative plan can be summarized below:

   1. Keep using the copper links as the last mile (NTU already owns
      that inside the campus). Use analog phones as the CPE device.
      Allocate a control room in each building to collect all the phone
      links.
   2. Deploy VoIP Gateway in each student dormitory, and connect the
      gateway to IP-PBX through campus fiber. There are totally 19
      dormitories now. The phone numbers were Centrex numbers, but may
      be turned to internal extension numbers in the next stage to save
      cost. 
      Figure of NTU IP-PBX Architecture :
      http://solomon.ipv6.club.tw/VoIP/TANet/ntu-centrex.png
   3. If any department plans to deploy a pure VoIP system (using IP
      phones as CPE devices), they will separate the data traffic and
      voice traffic. The layer 2 switch will also be upgraded to support
      PoE (power over Ethernet). The voice network will be connected to
      the IP-PBX with an independent fiber to make sure the voice
      service will not be interfered by data traffic, which may be huge
      in a university. :-)

They wish this plan can take into account all the considerations
including stability, extensibility, and voice quality.

We would like to consult your opinion for the two questions:

   1. Is there any member in Internet2 who has upgraded from Centrex to
      IP-PBX? Would they like to share their experience? Is there
      anything we should take caution during the transition?
   2. In choosing IP-PBX vendors, should we choose a tradition PBX vendor,
      and add an IP interface card? Or should we choose a vendor from
      data service, and build a server-based IP-PBX? It seems the former
      is more stable, but we are not sure of the extensibility of
      IP-based functions. As the later, we did not see large reference
      sites yet (more than 5,000 CPE devices) to make us confident of
      their capacity.

Any comments?

Sincerely,
Quincy Wu
Dec. 19