As you can see in Figure 3-1, security and scalability drive up cost and complexity. Although security and low cost are what informed users want in their DSL service, scalability with low complexity is desired by service providers.
Scalability is a bilevel consideration that includes
The service provider's own growth as DSL sales increase the number of DSL users
The growth of the DSL users' own networks, from adding computers in the home to business expansion
The earliest versions of DSL modems were bridges between a 10BASE-T Ethernet on the host side and RFC 1483 (now RFC ...