Principles for a Successful IP Transition: Speed
Consumers need fast networks that allow them access to, and choice of, a full range of services to meet their needs.
In replacing the public switched telephone network (PSTN), consumers need truly high speed networks with low-latency and jitter so that these networks are capable of fully supporting legacy PSTN services like faxing, modems, and text telephone (TTY) services that are sensitive to network quality.