利用交互式有线电视网接入因特网的框图如图1所示。它可以分成广域连接设备、网络中心设备和用户接入网设备三个部分。广域网连接设备包括天线、网桥、IP过滤路由器等,是用来使有线电视网同因特网连接,建立与其他因特网节点的联系。网桥和IP过滤路由器还组成防火墙,保证本地网不受外界侵犯,判定内部用户是否有权访问外部网络。除了通过DDN和X.25公用网外,有线 Figure 1 shows a block diagram of accessing the Internet using an interactive cable television network. It can be divided into wide area connection equipment, network center equipment and user access network equipment three parts. WAN connectivity devices, including antennas, bridges, IP-filtering routers, etc., are used to connect cable networks to the Internet and to establish contact with other Internet nodes. The bridge and IP filtering routers also form a firewall to ensure that the local network is not violated by the outside world and determine whether the internal users have access to the external network. In addition to the public network through DDN and X.25, wired