How can I bond 2 Point-to-point T1s with a PBX that requires Channels 13-24 on one T1 dedicated to it

In our company we have 2 remote offices that are currently connected to our main office by a point-to-point T1 in each remote office.  We have an Adtran router that splits the point-to-points and dedicates channels 1-12 to data and channels 13-24 to the PBX system (which the Comdial PBX system REQUIRES, don't ask me why....).  We need more bandwidth for business needs and want to bond two point-to-points together.  Adtran can do it, but we need 3 expensive 3rd party "IPTube" devices to pull this off.  I'd prefer a way to do this with a single router in each office. I need a way to still dedicate those specific channels to the PBX system.  I know that there is a WIC for Cisco routers that can drop/insert specific time slots, so if we created a channel group that took 13-17 from one half of the bond and 18-24 from the other half, could that work possibly?  If not, is there a way to specify 13-24 from one half of the bond and use the remaining channels bonded together for aggregated throughput?  We don't need the elevated burst speed.

If none of this will work, could anyone possibly recommend a way we can do this without loading our LAN room up with too much extra equipment?  Thanks!
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Reid PalmeiraConnect With a Mentor Telecom EngineerCommented:
you should be able to do this directly in the routers, couple of questions.

what model Adtran gear are you using and what firmware version ("show version" from enable mode)?

what NIM's (WIC in cisco parlance) do you currently have?

the point to point T1's, you say channels 13-24 are going to the PBX. Are these PSTN channels? or point to point connections from your PBX to another PBX (like a tie trunk)?

what protocols are you using on the point to point links?

If you have something like a dual T1 NIM on the Adtran box you can take in two T1's. Say on T1 "A" you have channels 1-12 going from main to site 1 via a PPP link and channels 13-24 on T1 "A" going to your PBX. On T1 "B" you setup channels 1-6 to go from main to site 1 via PPP 1 (using MultiLink PPP) then setup channels 7-24 to go from main to site 2 via a second PPP interface or whatever.

so then you've got 18 channels to each site, the routers at each site also need dual T1 cards, etc. and you keep your channels 13-24 for the PBX.

Or split it completely, see if you can get a fractional T1 for the PBX and two full T1's of point to point then you don't have to worry about splitting the TDM groups and setting up the MLPPP bonding. Some additional circuit costs are more expensive but at least you'd get the full T of bandwidth.
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