Research And Production Of ADSL Central Office-side Interface Card Based On ATM

With the popularization of light-guide fiber, the limit of bandwidth is disappearing off the transmission trunks. As a contrast, the loops linking customer terminals with the central offices are mostly traditional cupreous twisted-pairs, on which a data stream can only be transferred at a rate of no more than 64Kb/s using an analog MODEM. This capability is now far below people's needs to explore Internet or to link Intranet. Asymmetric Digital Subscriber Line (ADSL) is a new kind of broad band loop technology. With this technology, the available bandwidth on a two-wire loop can transfer two data streams synchronously, an upstream at a rate of 896Kb/s and a downstream at a rate of 8.192Mb/s.In this paper, an applied project of ADSL system is brought forward. Firstly, the discrete multi-tone processing in an ADSL central office-side interface card is detailedly introduced. The processing mainly includes timing, framing, interleaving, Forward Error Correction, Cyclic Redundancy Check, constellation encoding, Inverse Fast Fourier Transform processing, prefixing, D/A converting, and amplifying. Secondly, a kind of interface named UTOPIA Level 2 is used as the network interface, with which many ADSL devices are linked with one ATM layer. Each interface card contains 24 ADSL ports. Lastly, some important technologies that used in the design are introduced. They are Low Voltage Differential Signaling, live insertion and evulsion, system start synchronicity and fail restartable function, and signal integrity, and so on.There are still some deficiencies needed to be overcomed.