user manual

Configuring Headend Broadband Access Router Features
Headend Overview
MC-520
Cisco IOS Multiservice Applications Configuration Guide
Headend Overview
a WAN backbone and a hybrid fiber-coaxial (HFC) cable network. Installed at a Community Antenna
Television (CATV) head-end facility or distribution hub, the Cisco uBR7200 series is often located with
the following Internet service provider (ISP)-related components:
• Ethernet switch
• Proxy servers
• WAN router
• Gatekeeper/gateway equipment for Voice over IP (VoIP) applications
The Ethernet switch is used to reduce traffic on the WAN backbone.
The proxy server usually functions as a Web cache for host computers and as the Dynamic Host Control
Protocol/Trivial File Transfer Protocol (DHCP/TFTP) server for cable modems. DHCP for host
computers in the HFC plant is often handled over the WAN. The WAN router provides a gateway to the
data network.
For more information on these components and their requirements, refer to the “Supported System
Configurations” section of the “Cisco uBR7200 Series Overview” chapter of the Cisco uBR7200 Series
Hardware Installation Guide.
Note At the time of publication of this document, the Cisco uBR7200 series universal broadband
routers use 6 MHz radio frequency (RF) channel plans only. However, Cisco IOS Release
12.1 T will support 8 MHz channel plans with the Cisco MC16E cable modem card.
On the RF side, the downstream port on the Cisco uBR7200 series router is assigned a 6 MHz channel
slot at a standard broadcast CATV frequency. An upconverter device is used to convert the 44 MHz
intermediate frequency (IF) output to the assigned slot. In North America, carrier frequencies in the
forward plant are assigned from 54 MHz to 860 MHz. After upconversion, the signal is combined with
other analog TV or digital TV signals and sent to the transmit input of a fiber transceiver.
The receive input of the fiber transceiver is connected to an upstream port of the Cisco uBR7200 series
router. The upstream port is assigned a 0.2 MHz to 3.2 MHz frequency band in the reverse plant. In North
America, carrier frequencies in the reverse plant are between 5 MHz and 42 MHz.
The fiber transceiver is connected to up to 80 kilometers of optical fiber. Signals are carried in analog
form to a neighborhood, where they terminate in a fiber node. The fiber node, located on a telephone
pole or in an underground box, converts the optical signal back to an electrical signal, which is then
passed on to a two-way distribution amplifier system. The distribution amplifier system passes through
the neighborhood, where it is tapped off to individual CATV subscribers.
A coaxial cable delivers the signal from the tap to a drop box located on the subscriber premises. From
the drop box, the signal is split and cabled to consumer CATV appliances. One cable goes to the
television or set-top box; the other cable goes to a cable modem appliance such as a Cisco uBR900 series
cable access router, providing data and IP telephony services.
Figure 106 illustrates the topology of a typical HFC network supporting basic data services.