cts use much narrower bandwidth, 2 MHz, for upstream communication. The issue of shared bandwidth is also a disadvantage for the cable data systems. If the MSOs do not upgrade capacity as more people sign up, cable modem access speeds may become slower. Upgrading capacity is a fairly straightforward exercise for the MSOs. It is just a question of if the MSOs are willing to invest the money to make the upgrades. Another shared bandwidth issue is security. All the downstream traffic in a cable data network goes to all the cable modems in the network and all the upstream bandwidth is shared by all the cable modems in a local loop. IP and network protocols are used to make sure traffic is secure and routed properly. Many of the non-standardized first generation cable modems did not have encryption capabilities, so users were able to access other users traffic. Second generation modems and CMTS equipment are built according to the DOCSIS specification, which contains security and data encryption requirements. Still another disadvantage of using a cable modem is that the user does not have a choice of ISPs. The only ISP available to a cable modem user is the local cable company. This is because cable TV lines do not have 'common-carrier' status as do phone lines. However, there are some efforts underway to change this.The recommended application for cable modems is for private, not commercial use. Because of the shared bandwidth issue, most MSOs will not allow a subscriber to host a server with their cable modem. A cable modem subscriber who tried to host a server would use a great deal of the shared bandwidth, which would be detrimental to the other subscribers on the loop. But, for a private user, cable modem systems definitely offer the most bandwidth for the money. There are approximately 75 million cable TV subscribers in North America (Medin, 1999). As of August 1999, cable operators were offering two-way high-speed In...
