56k modems are voiceband modems capable of download speeds near 56 kbit/s (7 kbyte/s) when connecting to a service that has ISDN or other digital connection to the phone network. The upload speed is usually limited to 33.6 kbit/s though the late arriving V92 standard increased this to 48 kbit/s. Due to the design of public telecommunications networks higher speed dialup modems are unlikely to ever appear. Due to crosstalk considerations, the FCC in the United States and CRTC in Canada have placed a loudness limit on dial-up modems, resulting in a "speed limit" of 53 kbps. 56k modems can only work at 56K when there is only a single pulse-code modulation step in the path between the modem and the digital equipment at the provider. When this is not the case or when two 56k modems are used to communicate with each other they will generally fall back to 33.6 kbit/s V32bis. 56 kbit/s transmission exploits the fact that most telephone exchanges are interconnected with digit

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