Study of xDSL-based Local Access Protocols

• Main Authors: Chang-Chih Cheng, 鄭長志
• Other Authors: Jean-Lien C. Wu
• Format: Others
• Language: en_US
• Published: 2000
• Online Access: http://ndltd.ncl.edu.tw/handle/15522973350497878897

碩士 === 國立臺灣科技大學 === 電子工程系 === 88 === The two main kinds of broadband access network technologies are cable modem and digital subscriber line (DSL) (e.g., HDSL, ADSL, VDSL, etc.). It takes much time and money to deploy bi-directional cable access networks. Thus, the main products are unidirectional. Because the ADSL technology is generally applied in telecommunication networks and the replacement of 56k analog modems with ADSL is a trend, it is the future broadband access networks technology in an advantageous position. In this thesis, we investigate the architecture of ADSL-based access networks that uses PPP over ATM to carry IP packets. ATM physical layer that uses ADSL in the user site and SONET in the backbone network is the reference network model in this thesis. Using ATM cells to carry PPP packets causes a high overhead in bandwidth. Thus, the trend is to omit ATM layer and use PPP over SONET to gain more available bandwidth directly with the institution of PPP extension protocols recently. Because PPP over ATM only supports the connection establishment of permanent virtual circuits (PVCs) in ADLS networks, it makes the flexibility of connection establishments decreasing. Therefore, we use the PPP protocol and PPP extension protocols to support the functions of PVCs and even the functions of switched virtual circuits (SVCs). A PPP gateway device can be deployed to reduce the number of PPP connection establishments and increase connection flexibility. We first simulate connection establishment and discuss the flexibility with gateways, and then compare the transport overhead that uses the traditional ADSL access network protocol stack with the transport overhead that uses the protocol stack of PPP over SONET/ADSL. From simulation results, we conclude that the proposed protocol stack gives better flexibility in connections and bandwidth utilization.