 The term "headend" refers to the site where providers transmit content that they receive from satellites. A group of satellite dishes that receives content is referred to as a satellite farm. Central office switches and Voice over Internet Protocol (VoIP) equipment to support www.TechnicalPDF.com telephone services are also located at headends. Network Operations Centers (NOCs) capable of monitoring and making programming changes to the network as well as operations support systems can be located here as well. These centers typically serve 7 to 10 towns. Multiple hubs that distribute content are connected to the headend, as shown in Figure 4-7. Coaxial cable Transport network Distribution Distribution Fiberning Head end www.TechnicalPDF.com Coaxia Distribution Figure 4-7 A fiber/coaxial network with transport network linking distribution hubs to the headend. Hub Sites Hubs, also referred to as distribution hubs, are small buildings that are located closer to customers than headends. Local programming or frequently downloaded content might be located at a hub, which serves between 10,000 and 50,000 residences. In addition, cable modem termination systems, which manage traffic to traditional cable TV customers' modems and to the headend, are located at hubs. For more information, see the section "Using Cable Modem Termination Systems for IP Traffic" later in this chapter. A hub might serve a metropolitan area. Large towns would have two hubs. Linking Hubs and Headends via Metropolitan Area Networks Metropolitan Area Network (MANs) are also referred to as transport networks, or regional transport networks. They link hubs to headends. MANs typically operate over shorter distances than core, backbone networks. They carry a mix of voice, data, and video on demand, as well as television signals. Cable TV Metropolitan networks are www.TechnicalPDF.com made up of hybrid fiber/coaxial cabling with fiber for the core that transmits movies to neighborhoods, and parts of their networks in cities far from the headend. These c