Before revision: Poor-quality telephone lines, many of which were installed or last upgraded between the 1930s and the 1960s, often limit the speed of the network to bit rates of 26kbit /s or less.
After revision: Poor-quality telephone lines, many of which were installed or last upgraded between the 1930s and the 1960s, often limit the speed of the network to bit rates of 26 kbit /s or less.