 distances. Plan and plan for power to avoid circuit overloads and limit problems caused by dirty power. Make sure that plugs and circuit locations are convenient. Most videoconferencing group systems connect to an IP network or a private or public circuit-switched digital network. If, instead, the system will connect to satellite service the project manager will need to work closely with a supplier or room integrator. Such installations are potentially very complex and are outside the scope of this book. The type of circuit that will support the video application determines how a videoconferencing system connects to the network. Physical interfaces include EIA RS-449/422 and its associated dialing standard RS-366-A, the ITU-T V.35 (also able to support RS-366-A dialing), and X.21 interfaces. Interfaces also include RJ-11 or RJ- 45 (ISDN) and DS-1 (T-1). Of course, in the case of Ethernet, the connection will simply be RJ-45. Despite the growth of IP, the most common transmission for group systems is still ISDN. That said, significant IP-based video is in use over existing frame relay, however native IP (in the form of MPLS) is likely to supplant frame relay as circuits come up for renewal. For ISDN, V.35, RS0-530, and RS-449 are the most widely used physical interfaces. For IP, RJ-45 is the standard interface. The ITU-T X.21 interface, which is used primarily in Europe, operates at 56-384 Kbps and controls network dialing. One valuable feature of X.21 is its inherent dialing functions, which include the provision for reporting why a call did not complete. X.21 can be used to connect to both switched and dedicated networks. ISDN BRI, the most complex network interface to arrange, requires a NT-1 interface. An RJ-11 plug from the network plugs into the NT-1. On the other side, connection to the equipment is made via an RJ-45 plug. The specific type NT-1 required depends upon which CO manufacturer's switch provides the connection. Several companies make an NT-1 that can interface to standard central office (CO) tel