The good news for users working at home or in branch offices is the emergence of low-cost devices. At least one company plans to sell routers by mail order and at office-supply stores, but they're not likely to be a commodity soon. A primary factor in the buying decision is the number and types of ports. The minimum is one ISDN port and one LAN port, but most products contain many more of either. There are two kinds of ISDN ports.
Routers can also combine bandwidth from several channels in two connecting units.
The majority of products use Multilink PPP for this purpose, but a few use a proprietary linking scheme, which usually requires the same vendor's product at both ends of the connection. Most routers include an important money-saving feature called dial on demand. Dial on de mand establishes a connection only when a user attempts to transmit data. Compression can also save money by reducing the amount of time users spend transmitting data. Most router vendors offer compression, but some sell it as an optional add-on.