[Asterisk-Users] What the best Asterisk architecture for 900+ users?

[Alphonse Ogulla]

Hi good people,
A local Kenyan company wishes to improve its communication system by
embracing VoIP technology. They currently have a legacy PBX with 17
analogue trunk lines and about 900 extensions. Going by the tender
document, the main features they are looking for include:

01) Converged voice/data infrastructure fully compatible with ISDN.
i.e. single connection point for both data (PC) and voice (telephone)
02) Cost control, i.e. who can call where and when, class of service,
account codes, LCR and ARS.
03) Plug and play
04) Inter-branch connectivity (WAN)
05) Call detail reporting (call logging) software
06) Built-in voicemail
07) Built-in automated telephone operators [auto-attendant]
08) Built-in out of office notification
09) Built-in call conferencing
10) Built-in Direct Inward Dialing (DID) and Caller ID
11) Secretarial features i.e. ability for secretary to support several
individuals using single handset.
12) Built-in hunt & calling groups
13) Multi-line telephone handsets
14) Software integration (Built-in Computer Telephony Integration - CTI)
15) Built-in support for external/internal music on hold
16) Scalability to over 1400 extensions
17) Reliabililty i.e. real time operating system, hard drive mirroring
and redundant power supply.
18) PSTN (Telkom) line interfaces i.e. digital and analogue lines
19) PABX connectivity i.e. ability to connect to traditional PABX
using standards based protocol
20) Wireless handset/client.

The LAN network consists of 800 access points at 100Mbps on a 1
Gigabit Ethernet backbone. The WAN connection (VPN) to a remote office
is via a VSAT link at 64Kbps but is being upgraded to 128Kbps.

I'm interested in giving them a proposal with Asterisk at the core,
but I'm not sure of the architecture that best fits their needs. The
architecture I have in mind would consist of at least 1 or 2 E1/PRI
connections with DID to the Central Office then using a couple of rack
mountable Asterisk servers with fully redundant hardware, doing the
call processing bit in a distributed fashion. There are 2 branch
offices with each having less than 10 users.

Regarding IP phones, cost is not really the driving factor but rather
the ease of central management with respect to configuration,
troubleshooting and periodic firmware upgrades. The Polycom range look
very attractive.

So, what are your views on proposing Asterisk for this tender? How
many high-end Asterisk servers do you think will be required to serve
900-1400 users? Is it possible to manage several Asterisk servers as a
single virtual server? Your comments and remarks are welcome.

Thanks & regards,
Alphonse Ogulla
Nairobi, Kenya