use QPSK, 16-QAM, or 64-QAM, depending on the generation of DOCSIS stan- dard. (See Chapter 5, "Data Communications Basics," for information on modula- tion schemes such as QPSK and QAM.) DOCSIS also involves an Ethernet connection to the PC, SO data is transferred by using TCP/IP encapsulated in Ether- net frames between the cable modem and headend. DOCSIS includes a baseline privacy specification that relies on the use of both the 40- and 56-bit versions of DES. (See Chapter 9, "IP Services," for more information on security.) At this point, there are several generations of DOCSIS standards, including DOCSIS 1.0, 1.1, 2.0, and 3.0. The ITU has also adopted two of the DOCSIS vari- ants as international standards: DOCSIS 1.1 was ratified as ITU-T Recommenda- tion J.112, and DOCSIS 2.0 was ratified as ITU-T Recommendation J.122. DOCSIS 2.0 is backward compatible with DOCSIS 1.1. DOCSIS 1.0 DOCSIS 1.0 enables the cable TV industry to deliver high-speed data using cable modems. As with all the other DOCSIS standards, the main service with DOCSIS 1.0 is two-way access to the Internet. With DOCSIS 1.0, the upstream rate is up to 10Mbps over a 3.2MHz channel. For downstream data, the modulation technique specified is either 64-QAM or 256-QAM, and upstream it is either QPSK or 16-QAM. It is possible to deploy DOCSIS 1.0 on a one-way HFC network by implementing the return path over tra- ditional phone lines. Cable TV Networks DOCSIS 1.1 DOCSIS 1.1 was created to address the cable industry's desire to offer VoIP services. DOCSIS 1.1 includes key network technologies, including dynamic QoS, which is very important to VoIP, packet fragmentation, and enhanced security. (QoS is discussed in Chapter 10.) By supporting QoS, DOCSIS 1.1 allows for the provisioning of VoIP and interactive gaming. QoS also enables tier-based services such as higher speeds to heavy users. DOCSIS 1.1 also offers improved security and privacy, both of which are necessary to support voice ser- vices. For downstream data, the modulation technique specif