“Divide and rule”
As a horizontal cable in modern SCS, a four-pair balanced cable is used mainly. It is known that for signal transmission in Ethernet and Fast Ethernet networks, only two out of four pairs are used. The remaining pairs are virtually idle. The technical characteristics of modern cables in terms of the NEXT parameter are very high (see Fig. 1), which allows the use of free pairs for transmitting analog and digital signals without any noticeable effect on the operation of the main application. The American TIA / EIA-568-A standard does not provide for the use of free pairs in horizontal cable, but the international ISO / IEC 11801 and European EN50173 allow similar technical solutions, which are called cable sharing. To implement the principle of cable sharing, devices such as Y-adapters, dual adapter inserts, junction cords, etc. are commercially available. However, all of these devices are designed to transmit signals on 10Base-T Ethernet networks. The cable sharing principle is fully implemented in the AMP Communications Outlet (AMP CO) system manufactured by Tyco Electronics AMP.
The AMP CO system consists of special outlets with a unified connector (Edge Connector) into which the cable is plugged (all 4 pairs), and a large number of interchangeable adapter inserts (including even inserts for connecting a coaxial cable) to these outlets.
Over time, moving to various interfaces and network standards, it is only necessary to change the inserts (in sockets and patch panels) without affecting the cable system. It is possible to increase the total number of ports by changing the inserts to dual-port. At the same time, cable sharing technology is used – for most existing network standards (including Fast Ethernet 100Base-TX), you can connect two ports to one four-pair cable (two computers or two phones, or a computer and a phone), each of which uses two pairs. A possible further transition to the protocol, which uses all four pairs (for example, 1000Base-T) for data exchange, is again carried out by a simple change of inserts. On a contractual or licensed basis, the AMP CO system is supplied to such well-known manufacturers as Siemens (ICCS system), Legrand (Mosaic Aco system). It should be noted that the components of the AMR СО system are approximately 2 times more expensive than traditional solutions, and for this reason they are rarely used in small networks in our country.
To implement the principle of cable sharing, you can use components from other manufacturers. However, it is necessary to carefully comply with the requirements for cutting twisted pairs (promotion of twisted pairs with a seal of not more than 12 mm). This requirement is easily fulfilled when cutting one end of the cable into adjacent sockets of the patch panel, and the other end into a dual wall outlet.
Some experts doubt the possibility of sharing the cable to transmit local and telephone network signals. The main argument against this decision is the large (up to 90 V) amplitude of the ringing signal of the telephone line, which may interfere with LAN signals.