A telephony interface system has a controller and multiple communication interfaces to provide voice-over-packet telephone service with PSTN telephone service as backup. The kit includes a canal component fitted to the cavity. The stab flanks and load flanks form complex geometric profiles which in one version form an inclined Z-shape in profile and in another version form a reverse inclined Z-shape profile. The method is capable of generating a fingerprint which is susceptible to more simply and more efficiently synchronizing first and second data signals together. The cylinder unit has a piston and a main rod respectively connected to the push tube. The first and second gas diffusion layers sandwich a membrane-electrode assembly 2 in which catalytic electrode layers are provided on both surfaces of an electrolytic membrane from both sides, wherein a seal protrusion 12c is formed on a surface which is in tight contact with the membrane-electrode assembly 2.