PDF of this tutorialCable data network architecture is similar to that of an office LAN. A CMTS provides an extended Ethernet network over a WAN with a geographic reach up to 100 miles. The cable data network may be fully managed by the local cable operations unit. Alternatively, all operations may be aggregated at a regional data center to realize economies of scale. A given geographic or metropolitan region may have a few cable television headend locations that are connected together by fiber links. The day-to-day operations and management of a cable data network may be consolidated at a single location, such as a super hub, while other headend locations may be economically managed as basic hubs (see Figure 4).
Figure 4. Basic Distribution Hub
A basic distribution hub is a minimal data network configuration that exists within a cable television headend. A typical headend is equipped with satellite receivers, fiber connections to other regional headend locations, and upstream RF receivers for pay-per-view and data services. The minimal data network configuration includes a CMTS system capable of upstream and downstream data transport and an IP router to connect to the super hub location (see Figure 5).
Figure 5. Super Hub
A super hub is a cable headend location with additional temperature-controlled facilities to house a variety of computer servers, which are necessary to run cable data networks. The servers include file transfer, user authorization and accounting, log control (syslog), IP address assignment and administration (DHCP servers), DNS servers, and data over cable service interface specifications (DOCSIS) control servers. In addition, a super hub may deploy operations support and network management systems necessary for the television as well as data network operations.
User data from basic and super hub locations is received at a regional data center for further aggregation and distribution throughout the network (see Figure 6). A super hub supports dynamic host configuration protocol (DHCP), DNS (domain name server), and log control servers necessary for the cable data network administration. A regional data center provides connectivity to the Internet and the World Wide Web and contains the server farms necessary to support Internet services. These servers include e-mail, Web hosting, news, chat, proxy, caching, and streaming media servers.
Figure 6. Regional Data Center
In addition to cable data networks, a regional data center may also support dial-up modem services (e.g., 56–kbps service) and business-to-business Internet services. A network of switching, routers, and servers is employed at the regional data center to aggregate dial-up, high-speed, and business Internet services.
A super hub and a regional data center may be co-located and managed as a single business entity. A super hub is managed by a cable television service provider (TCI), while the regional data center is managed as a separate and independent business (@Home). In some regions, an existing Internet service provider (ISP) may provide regional data center support for many basic and super hub locations managed by independent cable data network providers.
A regional data center is connected to other regional data centers by a national backbone network (see Figure 7). In addition, each regional data center is also connected to the Internet and World Wide Web services. Traffic between the regional networks, the Internet and all other regional networks is aggregated through the regional data center.
Figure 7. National Network
