The S110M FXS module allows the TDM400P card to terminate analog telephones. 

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The S400M FXS module allows the TDM2400P card to terminate four analog telephones per module.Because of the modular design, a user can activate additional ports at any time with more S400M daughter cards. The S400M module passes all the call features 

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The VPMADT032 is a 128ms per-channel echo cancellation module for use with Digium telephony interface cards. 

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The X100M FXO module allows the TDM400P card to terminate analog telephone lines (POTS). 

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The X400M FXO module allows the TDM2400P card to terminate four analog telephone lines (POTS) per module. 

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