To take a look at Internet traffic statistics, including measurements for response times (delays) and packet losses, you can visit www.internettrafficreport.com Data Flow As discussed in the following sections, a number of important issues affect data flow in a network: The parts of the data circuit that comprises every network, including data terminal equipment (DTE), the data communications (or channel or circuit- terminating) equipment (DCE), the transmission channel, and the physical interface Modems and modulation Simplex, half-duplex, and full-duplex data transmission Coding schemes Asynchronous and synchronous transmission modes Error control The DTE, the DCE, the Transmission Channel, and the Physical Interface Every data network is a data circuit that has seven parts: the originating DTE, its physical interface, the originating DCE, the transmission channel, the receiving DCE, its physical interface, and the receiving DTE (see Figure 5.1). The transmis- sion channel is the network service that the user subscribes to with a carrier (e.g., a dialup connection with an ISP). Data Flow Physical Physical Interface Interface Point A Point B Transmission Channel Telephone Lines Modem Mainframe Computer Modem Personal and Front-End Processor Computer Figure 5.1 The DTE, DCE, transmission channel, and physical interface The DTE transmits data between two points without error; its main responsi- bilities are to transmit and receive information and to perform error control. The DTE generally supports the end-user applications program, data files, and data- bases. The DTE includes any type of computer terminal, including PCs, as well as printers, hosts, front-end processors, multiplexers, and LAN interconnection devices such as routers. The DCE, on the other hand, provides an interface between the DTE and the transmission channel (i.e., between the carrier's networks). The DCE establishes, maintains, and terminates a connection between the DTE and the transmission channel. It is responsible for ensuring that the sign