er existing North American cable TV networks using existing RF equipment. It combines 64 or 256 QAM modulation of the downstream signal, a variable length interleaver, trellis coding, and Reed-Solomon error correction coding. For the downstream transmission convergence sublayer, DOCSIS defines MPEG-2 transport to enable both video and data signals in a single multiplexed bit stream that occupies one analog channel. DOCSIS accommodates most cable network Video Communications: The Whole Picture architectures because it uses a range of symbol rates including QPSK or 16 QAM modulation, Reed-Solomon error correction coding, and transmit power automatically adjusted by the MAC. The DOCSIS MAC enables initializing new modems on the network, sharing upstream bandwidth between active modems, periodic ranging and power adjustment to decrease the effects of temperature on the cable plant, and modem management. The DOCSIS standards for Baseline Privacy use 56-bit DES encryption of data traffic. It leverages the RSA public-key encryption algorithm for key management and distribution, with a key size of 768 bits for DOCSIS 1.0 and 1024 bits for DOCSIS 1.1. DOCSIS RF-return cable modems forward packets using IEEE 802.1D forwarding rules, as modified by the DOCSIS specifications. Telco return modems forward packets using IP forwarding rules. In both modes of operation, these modems are capable of layer two and layer three packet-filtering, per operator-defined filter rules. The DOCSIS specifications were developed to enable hardware and systems interoperability, and automated configuration and management. Cable Modems and Cable Modem Termination Systems (CMTS) from numerous vendors can use the DOCSIS specifications to operate on the same network. In the DOCSIS model, a cable modem is authorized by the CMTS for use on the network, and configures itself according to parameters that it receives from the headend, without user involvement. When the cable modem is powered up and logged on to the network for the first time (or if the d