Figure 2.5 indicates the transport protocols used by some popular Internet applications. We see that e-mail, remote terminal access, the Web, and file transfer all use TCP. These applications have chosen TCP primarily because TCP provides a reliable data transfer service, guaranteeing that all data will eventually get to its destination. We also see that Internet telephony typically runs over UDP. Each side of an Internet phone applications needs to send data across the network at some minimum rate (see real-time audio in figure 2.4) ; this is more likely to be possible with UDP than with TCP. Also, Internet phone applications are loss-tolerant, so they do not need the reliable data transfer service provided by TCP.