The technology of Asynchronous Transfer Mode (ATM) is a backbone network
technology that is introduced to transfer voice, video, and data information.

virtue of its flexibility and support to multi-media service, ATM is regarded as the
core technology for realizing broadband communication.

Digital Subscriber's Line (DSL) is a technology providing high-speed data
transmission over the copper wire. It includes Asymmetric Digital Subscriber Line
(ADSL), High-bit-rate Digital Subscriber Link (HDSL), Very High Rate Digital
Subscriber Line (VDSL), and Symmetric Digital Subscriber Line (SDSL). These DSL
technologies are different primarily in terms of the signal transmission speed and
distance and their symmetry state (that is, whether their uplink and the downlink
speeds are the same).

The ATM physical layer lies at the bottom of the ATM reference model. Though it
involves the specific transfer medium, its functionality does not rely on the
adopted transmission mechanism and speed. Rather, it primarily delivers the
significant cells and the associated timing signals between the upper layer and the
transmission medium. The speeds of the physical access media have been
standardized by the concerning international standard organization. For example,
there are ATM OC-3c/STM-1, and ATM E1/T1. As most DSL applications are
ATM-based, they can provide the services integrating the advantages of ATM and
the low-cost transmission feature of DSL. So far, the DSL technologies have been
widely adopted for the broadband accessing.

ATM Interfaces available

for a 3Com Router

3Com routers can provide the following interfaces:

■

ATM OC-3c/STM-1 interface module based on SONET/SDH

■

ATM ADSL interface module based on the ADSL technology