A variable rate transmission system where a packet of variable rate data is transmitted on a traffic channel if the capacity of the traffic channel is greater than or equal to the data rate of the packet. The cock body has a circular tube part that has a first portion and a second portion arranged parallel to each other along the axis of the circular tube part. Since this metallic complex adsorbs oxygen as the oxygen partial pressure at the fuel electrode increases and desorbs oxygen as the oxygen partial pressure decreases, oxygen produced when a reverse voltage is generated can be removed efficiently. The first end is secured to an associated pivot while the second end is movable along the arcuate path. A length of the converting module is substantially equal to that of the first substrate in the first axial direction, and a width of the converting module is smaller than a length of the first substrate in the first axial direction. Optionally there is included an oxygen scavenger.