PDF of this tutorialFrom a high-level view, the DSL infrastructure consists of the LEC providing the local loop , the NAP’s DSL access multiplexer (DSLAM) and ATM network, and aggregation routers that bind packet networks with the NSP’s Internet protocol (IP) networks (see Figure 2). NSP routers using ATM or private lines eventually feed data packets farther upstream to content providers.
Figure 2. High-Level View of the DSL Supply Chain Infrastructure
As DSL comes into greater prominence, end-to-end visibility of networks and services has become mandatory for managing concentrated networks and fulfilling service level agreements (SLAs).
With DSL, packet concentration occurs within DSLAMs, ATM networks, and aggregators—before packets can even proceed to the NSP. However, virtually none of these devices supports IP, with packets usually encountering first an IP element in the aggregation router.
Unfortunately, IP–centric systems for management and testing cannot support the visibility into data streams needed to deliver and assure DSL services. Previous IP access technologies employed an array of different service assurance techniques. For example, service providers have used traditional private-line service assurance solutions successfully in dedicated access networks, where no concentration or oversubscription occurs. Dial networks rely on significant amounts of concentration, but their all–IP nature enabled service providers to use proven inband IP diagnostic tools for troubleshooting and fault and performance management.
