use the total bandwidth is shared by all cable modems in a local loop. This means all downstream data is received by all the cable modems in a loop. Each cable modem uses the Ethernet frame format to filter out the data it needs from the downstream of data. The CMTS encrypts the payload data of link-layer frames transmitted on the cable network. The Security Association (SA) assigns a set of security parameters including keying data to a cable modem. All of the upstream transmissions from a cable modem travel across a single upstream data channel and are received by the CMTS. In the downstream data channel, the CMTS must select appropriate the appropriate SA parameters based on the destination address of the target cable modem. Baseline privacy employs the data encryption standard (DES) block cipher for encryption of user data. The encryption can be integrated directly within the MAC hardware and software interface. Cable modem technology offers tremendous advantages. A cable modem user can get the performance of a T-1 line at a fraction of the cost. Current cable modem service connection speeds are much greater than that of a dial-up ISP at roughly the same price. Dial-up ISPs offer 56 Kbps connections for around $20 per month. Emerald Coast Cable TV, the MSO for the Fort Walton Beach, Florida area currently charges $30 a month for unlimited Internet access with a cable modem. A cable modem offers speeds between 500 Kbps to 1.5 Mbps. Even the low end of this range is an order of magnitude faster than a 56 Kbps connection. Cable modems currently retail for approximately $300, but the prices are forecast to drop rapidly. Emerald Coast Cable TV charges $15 a month to rent a cable modem. In addition to their blazing speed, another advantage of cable modems is constant connectivity. Cable modems are online as soon as the computer is turned on. The cable modem user does not have to dial-in to begin an online session. The...
