u2018 fax image signals u2019 may include inter alia signals relating to the fax u2018 in message u2019 procedure itself i e t 30 phase c signals and to t 30 phase b type u2018 pre message u2019 signals such as u2018 training check frame u2019 u201c tcf u201d v 34 u2018 line probe u2019 signals and v 34 u2018 primary channel u2019 equalizer training u201c trn u201d signals signals belonging to the second type of signals may be conditionally relayed in demodulated form or are said to be u2018 transparently u2019 transferred over ip between gateways by using pcm encoding frp format and pcm decoding a determination as to how and when to process i e performing demodulation or pcm encoding the incoming fax signal may be made by judging such as by a u2018 state machine u2019 a currently and historically based on previously detected or demodulated fax signals and received frp data from the ip network the judging may also be based on the gateway capabilities and on the estimation of resources available for performing demodulation some judgment is traditionally performed by various types of gateways for anticipating a current step in a specific fax communication session this judgment is essential because a gateway must.