ata frequency has been changed), it automatically scans the downstream frequency spectrum to locate the data channel. If the cable modem has previously accessed the network, it will have stored the previous session frequency and will immediately tune to the data channel. Once it finds the DOCSIS data signal, it looks for a message that contains the basic parameters for the upstream channel (e.g., frequency, modulation, symbol rate, FEC parameters.). The cable modem then transmits a message to the CMTS with a request for additional information that will enable it to connect to the network. Through a series of messages and interactions, the cable modem establishes IP connectivity using DHCP, and then receives additional configuration parameters via TFTP SO that it can configure itself. Once the cable modem is configured, it registers with the CMTS and becomes authorized to use the network. Optionally, the final step of the initialization is establishment of the parameters to use Baseline Privacy. Once configured and authorized, it is a standard Ethernet network device. The DOCSIS downstream transmission specification is based upon ITU J.83B technology developed for digital TV applications. In 64 QAM mode, the maximum bandwidth available on a 6 MHz channel is approximately 27 Mbps after error correction. When running in 256 QAM mode, the system can support rates up to 38 Mbps. It can be set anywhere in the DOCSIS downstream spectral range of 88-860 MHz. Upstream, the cable modem supports two modulation formats, QPSK and 16 QAM, and 5 different symbol rates. The spectral range for upstream transmission is 5-42 MHz. Circuit-switched Networks The structure of the network is IP over Ethernet. The primary standards incorporated in the DOCSIS system architecture are IEEE Ethernet standards 802, 802.2, 802.3, and RFC-791 IP data standards. Once the transmission protocols have been established, the network operates transparently as an Ethernet network. DOCSIS cable modems are software upgradable during initialization or on 