CAP operates a national radio network of HF (SSB) and VHF (FM) radio repeaters. Optical amplifiers have several significant advantages over electrical repeaters. There are also digital amateur TV repeaters that retransmit digital video signals. Active Radio Amateurs maintain wireless repeaters located on Mt Bruce. Now, most telecommunications cables are fiber optic cables which use optical repeaters (below). Many amateur radio repeaters identify with Morse, even though they are used for voice communications. Some wireless repeaters have a power outlet. Globalstar satellites are simple "bent pipe" analog repeaters, unlike Iridium. Upper trims included power folding heated mirrors with turn signal repeaters. The coaxial cable was replaced with point-to-point links connected by Ethernet repeaters or switches. Also, the ISS has amateur radio repeaters and radio location services on board. By using repeaters very large RS-485 networks can be formed. Users should avoid using these channels to avoid interfering with repeaters. Various repeaters (hubs) may use slightly different implementations and operate differently. The invention of audion tube repeaters around 1916 made transcontinental telephony practical.