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Chapter 2Overview of current CATV network pwith a cheap Network Interface Card (NIC) inside, directly connected to a cablemodem through an Ethernet connection (10BaseT) or Universal Serial Bus (USB).The second alternative is to have two PCs connected to a single cable modem. Mostproviders have instructions on how to accomplish this and require a home user todownload additional software (such as Network Address Translator-NAT [107]) toaccommodate the dual connection on a single modem [9]. This means that the MACaddress of the packets coming from a PC (without cable modem connection) shouldbe changed to the MAC address of the PC’s NIC card with cable modemconnectivity. This is because most cable modems only forward traffic to the CATVnetwork from a single MAC address.The third alternative is to have a router, bridge or switch connected to the cablemodem. With this configuration, the cable modem is attached to the network and therouter/bridge/switch is responsible for forwarding traffic onto the cable system usingits MAC address. This is an attractive solution but it is more expensive because acostly device is required.A last configuration presented is to have two NIC cards in a single PC and thecorresponding software (NAT) to forward traffic from other PCs. With one NIC cardthis PC has connectivity with the cable modem. With the other NIC card, a 10/100Base Hub can be connected, which in turn interacts with others PCs. This is aninexpensive solution and allows multiple PCs to have interconnectivity with theoutside world.According to [9], the use of the PC with the two NIC cards is not necessary since thehub can be connected directly to a cable modem. The hub will act as a bridgingfunction onto the cable modem, and concentrate the traffic through the individualdevices.• Internal cable modems are cable modems that are built into a PCI add-on card. Itmay be the cheapest implementation possible, but there are some drawbacks. Thedesign only allows a cable modem to connect to one computer. In addition, internalcable modems do not isolate the connection to the cable network from the AC powersystem. This can cause major problems in some cable systems.2-8