Design network for my office

We’re preparing to build our network’s phone with Asterisk .
We have 2 offices: A office ( 20 analog phones) and B office ( 4 analog phones).
Between A and B office will connect by our WAN.

We are considering to build in

  • A office:
  • Asterisk server
  • VOIP gateway FXS 24 ports
  • 20 analog phones
  • B office
  • ATA 4 analog ports
  • 4 analog phones

And we are wondering one problem about PSTN interface.
Do we should integrate PSTN interface on VOIP gateway FXS or on Asterisk server?

If we integrate PSTN interface on Asterisk server, we will have to buy another PSTN card?
But it’s not a saving money solution.

If we integrate PSTN interface on VOIP gateway FXS, can we configure to route dial plans to use Asterisk first and after that will go to VOIP gateway FXS. That mean all functions of PBX will be used by Asterisk server. VOIP gateway FXS only has a function of an adapter (convert analog to VOIP).

Which way do we should to choose?

Thanks for your advise.

I would throw the analogue phones out and go all IP. Once you buy all the ATAs and SIP gateways you need to make the analogue phones work, you’ll be near the same cost as putting an IP phone on everyone’s desk. You also have the additional problem of training the users to use DTMF feature codes to do transfers or call forwarding or voicemail rather than having programmable softkeys on the IP phone. You can buy Cisco SPA901’s new for $60 or refurbished for $40. You’ll pay the same price for individual ATAs. A 24-port FXS SIP gateway will cost you around $1200, or $50 per port. Approximately the same price as an IP phone.

It’ll be break-even for either solution, but an all IP solution will get you so much more flexibility and ease of use.

Definitly IP phones are the best things.

If you insist on using analog phones, I would recommend using external analog-VoIP gateways.

1] you dont use FXS gateway to integrate to the PSTN… you need FXO ports to integrate to POTS service from the locsal telco…

2] I would go SIP TRUNK from the asterisk server to the PSTN… you can either order an ISP that will provide MPLS, or can provide some type of QoS on their side of the network… or you can set up your own data router to provide QoS on your end towards the pipe…

3] using a 24 port FXS Gateway , depending on the brand can cost as mentioned just about as much as a lower end IP set…
the Lower end Ciscos or Aastra 673x series are decent entry level IP sets and provide displays and hard keys for transfer, hold, conf, etc…