nd Time Warner Cable are examples of MSOs in the United States. Asymmetric Channels MSO offerings for residential-consumer Internet access are often asymmetric, with higher speeds in the downstream channel from the cable provider to the subscriber, and lower speeds upstream from the subscriber to the provider. Splitting the frequencies into different ranges enables the same coaxial cables to be used for both sending and receiving signals. Unlike fiber cabling, for which separate strands of fiber are used for sending and receiving, a separate coaxial cable does not need to be installed for the reverse, upstream channel. Using Cable Modems to Access the Internet The basic functions of cable modems are to convert digital signals from computers or data networks to those compatible with coaxial cabling and to convert radio frequency (RF) from cable TV networks to digital signals suitable for Internet access. In cable TV, electromagnetic waves carried on coaxial cabling are referred to as RF signals. Carrier Networks The Cable Modem "Handshake" Cable modems perform a "handshake," an exchange of signals before data is transmit- ted to and from the Cable Modem Termination Systems (CMTSs) located at the cable operator site. (See the following section for information regarding CMTS equipment.) Complex signaling, use of frequencies, the speed at which to transmit, and authentica- tion are agreed upon between the two devices. At startup, the network checks the user's login before allowing access to the Web or certain web sites. Using CMTS for IP Traffic CMTSs are located at the cable or distribution center (the hub). They modulate and demod- ulate (hence, the term "modem") digital voice and data signals and place them on cable infrastructure. Modulation is the technique of making digital signals suitable for radio frequencies (electromagnetic waves) that carry signals on cabling infrastructure. CMTSs demodulate signals received from customers to make them suitable for transmission on a cable company's fiber-optic rings, whic