Though it is not necessary to understand how the Internet works, the basic differences between the Internet and continuous data transmission should be understood. There are two key differences:

• Continuous data transfer concepts such as the bandwidth assigned to each user become meaningless, at least for Internet traffic. The Internet provides bandwidth on demand except it really transfers packets in bursts. There will be delays in receiving a file or burst of data if there are many users. These delays, which increase with traffic load, are a measure of the quality of service (QoS).
• Most forms of Internet file transfer require Internet protocol (IP) acknowledgments (ACKs). Delays or latency in returning ACKs back to the information source slow the downstream file transfer.

The downstream communication uses the transmission control protocol (TCP)/IP. The customer's computer acknowledges the receipt of packets by sending an ACK signal upstream. TCP uses a form of data flow control called a sliding-window protocol. This allows very fast downstream bursts suited to the high bit rate of the downstream channel (but lower average rates scaled to shared channels and the computer's ability to receive data at 1–Mbps to 2–Mbps). It optimizes burst communication where the latency or the delay time in receiving the ACK impacts the downstream speed.

The following are effects of TCP/IP on cable modem systems:

• TCP/IP is much more tolerant of occasional brief losses of downstream communication caused by interference than a television signal because it can request retransmissions.
• A return path is needed to acknowledge the transmitted packets as well as the request files.
• Traffic is asymmetric—that is, a 10–Mbps wireless downstream path still yields fast downstream file transfers even with a low bandwidth return path such as a 14.4–Kbps phone connection.
• A wireless downstream path with a telephone return path is a viable way to provide service. (Wireless return options are in their infancy due to the cost of the equipment and limited available bandwidth. They offer lower latency and in most cases a higher upstream speed for file transfers in business applications.)
• Both telephone and wireless return paths can introduce additional factors that cause high latency resulting in slower downstream speeds. For example, V.34 28.8-Kbit telephone modems have greater latency than V.32 14.4-Kbit telephone modems. Similarly, some cellular wireless and satellite data services have extreme latency and, as a result, give slow file transfers.

The broadband modem system can contribute round-trip latencies that vary from 25 msec for wireless return and upwards of 125 msec for telephone return. ACK is about 40 bytes long for telephone return systems and about 80 bytes long for wireless return due to their different protocols.