Internet telephony and modem delay

The vast majority of consumer Internet access is via dialup modems. These modems are a primary source of the delay experienced on voice over IP cells. The author focuses on understanding the causes of delay within analog modems, with the objective of developing recommendations to minimize delay for VoIP applications. First, the relative importance of modem delay is assessed versus other causes of VolP delay (e.g., PC client, IP network), and delay from other access types (e.g., ISDN, cable modems). Second, the characteristics of VoIP data streams are examined as a key determinant of modem delay. Third, the internal operation of modems is examined with respect to delay when transmitting VoIP data streams. Finally, some recommendations and conclusions are presented.