Connect Two S-series IP PBX

I have two S-series IP PBX - S100 and S20.
All the extensions under S100 are in the format 1xx.
All the extensions under S20 are in the format 2xx.
S20 register as an extension(194) in S100 via SIPTrunk.
S100 register as an extension(294) in S20 via SIPTrunk.
Calls between them work well.
But i have little problem:
When users call from 1xx to 2xx, or backward, caller ID is not take correct by the remote station.

Can anyone help me?







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