Transmission Control Protocol (TCP), the most popular transport layer communication protocol for the Internet, was originally designed for wired networks, where bit error rate (BER) is low and congestion is the primary cause of packet loss. Since mobile access networks are prone to substantial noncongestive losses due to high BER, host motion and handoff mechanisms, they often disturb the traffic control mechanisms in TCP. So the research literature abounds in various TCP enhancements to make it survive in the mobile Internet environment, where mobile devices face temporary and unannounced loss of network connectivity when they move. Mobility of devices causes varying, increased delays and packet losses. TCP incorrectly interprets these delays and losses as sign of network congestion and invokes unnecessary control mechanisms, causing degradation in the end-to-end good put rate. This chapter provides an in-depth survey of various TCP enhancements which aim to redress the above issues and hence are specifically targeted for the mobile Internet applications.
Key Terms in this Chapter
Mobile IP: A modified IP protocol to allow users on the move to access the backbone network like the Internet.
Throughput: The ratio of number of packets successfully transmitted to amount of time required to complete the communication.
Goodput: The ratio of number of packets successfully transmitted to number of packets actually transmitted.
Energy Efficiency: The ratio of minimum energy consumption required to transmit a certain amount of data to that of actual energy consumption.
Congestion Window: The maximum number of TCP packets that a sender is allowed to send at a time to the network, or in other words, it is the maximum carrying capacity of the network.
TCP: A true end-to-end, connection-oriented protocol for providing reliable and ordered delivery of packets to the application, bypassing the unreliable nature of the Internet.
DUPACK: An acknowledgement packet that contains the sequence number of last acknowledged packets.