Customer Premises Networking · Line impedance changes due to phones being on-hook or off-hook 362 Based upon HomePNA field studies, it is estimated that HomePNA will operate reliably at the rated maximum bit rate upon initial installation in more than 90 percent of U.S. homes, at a reduced bit rate for about 5 percent of homes, and not work reliably for about 5% of homes. Many of the cases of trouble with HomePNA are due to noise from telephony equipment (fax, modem, caller-ID, and answering machine), which can be resolved by placing an in-line low-pass filter in series with the telephony device. On rare occasions, HomePNA causes audible noise in telephone receivers; this too can be resolved by placing an in-line low-pass filter in series with the telephone. Another source of trouble is the home telephone wiring being either too long or having too many long bridged taps. As a rule, the maximum wire distance between HomePNA devices is 500 ft. Inside telephone wiring often takes indirect routes so that two outlets that appear to be only 50 ft apart could be hundreds of feet apart in the wiring. HomePNA offers the lowest cost home LAN solution using existing wiring ($38 as of the time of this printing). However, it does not work well in all homes, and there may not be a phone wall jack accessible at some of the locations where an information appliance resides. The frequency bands used by HomePNA and VDSL overlap to a large degree. Analysis of Home- PNA and VDSL located at the same premises indicate that both systems would be greatly impaired unless the two systems use separate inside wiring and a low-pass filter was placed at the entrance to the premises to prevent the HomePNA signals from exiting to the outside wiring. This would require installation by a skilled technician. There is a possibility for adverse interference between nearby customers sharing the same distribution cable. One customer with VDSL and a neighbor with HomePNA could experience interference problems. This could be especially acute for an MDU (multiple dwelling unit, such as an apartment building). Radio frequency egress from HomePNA may be a concern in some countries due to radiation from poorly balanced inside wiring. Security is another concern for HomePNA; in rare instances a neighbor in the same telephone distribution