Usually this is not a problem since most ISPs offering dial up services have direct connections to the Public Switched Telephone Network (PSTN). The V.90 modems provide an upstream data transfer rate of 33.6 kbps based on the V.34 standard. Voice modems have been continuing to push the limits of technologies however there is a limit to bandwidths that can be achieved using voice band technologies.
Raising demands on part of the users for higher bandwidths to support increasingly content rich media have led to creation of other technologies that support higher bandwidths and data transmission rates over exiting Public Switched Telephone Networks (PSTNs). The data access patterns for most residential users are asymmetric in nature, requiring availability of different levels of bandwidths in the upstream and downstream direction. Usually common activities like web browsing involve higher transfer of data from the source to the destination, i.e. from Central Offices (COs) to subscriber locations. Business user’s data access patterns differ from those of home users. Business users use data in a symmetric pattern with equal amounts of data being transferred both upstream and downstream. Increasing customer requirements have led to the development of newer technologies like DSL (Jones, 2006; Tanenbaum, 2003).