Cisco Systems uBR7246 User Manual
Configuring Cisco uBR7246 Universal
Broadband Router Features
Cisco uBR7246 universal broadband features enable the Cisco uBR7246 universal broadband router
to communicate with a hybrid fiber coaxial (HFC) cable network via a Cisco MC11 cable modem
card. Cisco MC11 cable modem cards allow you to connect cable modems on the HFC network to
a Cisco uBR7246 in a Community Antenna Television (CATV) headend facility. The modem card
provides the interface between the Cisco uBR7246 protocol control information (PCI) bus and the
radio frequency (RF) signal on the HFC network. For a description of the commands used to
configure universal broadband features, refer to the “Cisco uBR7246 Universal Broadband Features
Commands” chapter in the Voice, Video, and Home Applications Command Reference.
The MC11 cable modem cards consist of the following components:
• One downstream cable F-connector port—The downstream port supports quadrature amplitude
modulation (QAM) speeds of 64-QAM, or 6 bits per symbol. A symbol is the basic unit of
modulation in CATV systems.
• One upstream cable F-connector port—The upstream port supports quadrature phase shift keying
(QPSK) modulation, or 2 bits per symbol.
• Cable Media Access Control (MAC) unit—The cable MAC frames and encrypts the downstream
signal for RF transmission and passes the signal to the downstream physical layer (PHY).
Reverses the signal framing and encryption on the upstream signal from the upstream PHY.
• Downstream PHY unit—The downstream PHY generates a modulated, intermediate frequency
(IF) output signal at a frequency of 44 MHz and passes the IF signal to an external IF to RF
upconverter installed in the downstream path.
• Upstream PHY unit—The upstream PHY receives the modulated, upstream signal at a frequency
of 5 MHz to 40 MHz and passes the signal to the cable MAC to remove the framing and
encryption formats.
• Spectrum manager—The spectrum manager continuously monitors the noise in unused upstream
channels. If the signal-to-noise ratio reaches an unacceptable level on a particular channel, the
spectrum manager will automatically assign a new upstream channel to the cable modem using
that channel. This feature is referred to as frequency agility.
You must install at least one Cisco MC11 cable modem card in the Cisco uBR7246 chassis to
establish communication between the Cisco uBR7246 and the HFC network.
Figure 38 shows the network topology for the modem card and illustrates network connections using
the Cisco uBR7246.
Configuring Cisco uBR7246 Universal Broadband Router Features VC-133
Figure 38 Topology for uBR7246 Universal Broadband
Proxy server
Analog TV
signals
Digital TV
signals
100BT
Cisco
uBR7246
US-RF
5-42 MHz
WAN
ATM, 100BT, 10BT
100BT
100BT
IF
Upconverter
RF
DS-RF 54-860 Mhz
Combiner
Fiber
Transceiver
Internet
ISP
MSO: Multiple Service Organization
VC-134
80 km
Fiber node
(Telephone pole,
underground box)
Two-way
distribution
amplifier
Voice, Video, and Home Applications Configuration Guide
1000 ft
Tap
Drop box
Cable modem
(Cisco uBR904)
11278
Description of Cisco uBR7246 Cable Router
As shown in Figure 38, the Cisco uBR7246 serves as an interface between a WAN backbone and an
HFC cable plant. Typically installed at a CATV headend, the Cisco uBR7246 is often located with
the following internet service provider-related components:
• Ethernet switch
• Proxy server
• WAN Router
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 the 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.
On the RF side, the downstream port is assigned a 6-8 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
between 54-860 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 uBR7246.
The upstream port is assigned a 0.2-3.2 MHz frequency band in the reverse plant. In North America,
carrier frequencies in the reverse plant are between 5-42 MHz.
Description of Cisco uBR7246 Cable Router
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
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. Typically, there are
500-1500 homes passed per fiber node.
A coaxial cable delivers the signal from the tap to a subscriber’s drop box. From the drop box, the
signal is split and cabled to consumer CATV appliances. In addition to analog or digital television,
the subscriber obtains data services using a cable modem appliance, like the Cisco uBR904 cable
modem.
Benefits of Cisco uBR7246
The Cisco uBR7246 features bring value to the digital broadband network by:
• Enabling the cost-effective deployment of advanced routing capabilities deep into the cable
network.
• Combining the power and functionality of a Cisco 7200 series router with the high-speed network
access of a Cable Modem Termination Shelf (CMTS). By combining these two essential
functions, the Cisco uBR7246 router conserves valuable headend rack space, and it allows cable
operators to deploy routing capability in every CMTS location, which improves network
performance.
Configuring Cisco uBR7246 Universal Broadband Router Features VC-135
List of Terms
• Providing a universal platform for deployment of both current and future modem technologies
• Leveraging Cisco’s industry-standard routing hardware and Cisco IOS software to deliver
The Cisco uBR7246 cable modem cards are fully compatible with the Data Over Cable System
Interface Specification (DOCSIS) established by major North American cable operators through the
Multimedia Cable Network System (MCNS) consortium.
The Cisco uBR7246 supports both two-way and telephone return modems on a single downstream
channel. The Cisco uBR7246 therefore allows both one-way and two-cable plants to provide cable
modem service, and gives cable operators the flexibility to roll out service in systems that are only
partially upgraded to two-way.
List of Terms
Community Antenna Television (CATV)—Broadband transmission facility.
via modular upgrades while protecting the operator’s invested capital.
advanced network services and applications. The Cisco uBR7246 uses the same port adapters as
the Cisco 7500 and Cisco 7200 series routers, and they are fully interchangeable. This
adaptability and flexibility allows the operator to configure the network with any interface
desired, including Ethernet, Fast Ethernet, FDDI, ATM, packet-over-SONET, and serial.
Downstream—Frequency multiplexed band in a CATV channel that distributes signals from
headend to users. In this instance, downstream refers to the data flow from the Cisco MC11 modem
card in a Cisco uBR7246 to the user’s cable modem.
Headend—Originating point of a signal in a Cable TV system.
IF—Intermediate frequency. Intermediate electromagnetic frequencies generated by a
superheterodyne radio receiver.
HFC—Hybrid fiber coaxial cable. Distribution cabling concept using both fiber optic and coaxial
cable. Fiber is used for the backbone distribution medium, terminating in a remote unit where
optoelectrical conversion takes place. The signal is then passed as data to coaxial cables that carry it
to its destination.
QAM—Quadarture amplitude modulation. Modulation technique that allows data-encoded symbols
to be represented in 16 or 32 different states.
QPSK—Quaternary phase shift keying. Compression technique used in modems and wireless
networks, allowing the transmission of 2 bits per symbol. QPSK provides a 2:1 compression ratio,
resulting in double efficiency for the circuit being used.
RF—Radio frequency. Group of electromagnetic energy whose wavelengths are between the audio
and light range, usually between 500 KHz and 300 GHz.
Symbol—Phase range of a sine wave.
Upstream—Frequency multiplexed band in a CATV channel that distributes signals from
transmitting stations to headend. In this instance, upstream refers to the data flow from a cable
modem to the Cisco MC11 modem card in a Cisco uBR7246.
VC-136
Voice, Video, and Home Applications Configuration Guide
Prerequisite Tasks
Before you can configure Cisco uBR7246 universal broadband router features, you must first:
• Make sure that your current network is designed to support broadband transmission. At the very
least, your network must include the following:
— Computer on the WAN side of your Cisco uBR7246 configured as a DHCP server to assign
IP addresses to cable modems on the HFC network.
— Cisco uBR7246-compatible IF-to-RF upconverter installed in the downstream data path at
your headend site. The upconverter is installed between the Cisco uBR7246 and the
combiner.
Note The combiner refers to all cables, amplifiers, and taps at the headend or cable distribution
center that connect the Cisco uBR7246 to the hybrid fiber coaxial (HFC) network.
— Diplex filters installed in the downstream RF path between the cable modems and the cable
modem cards in the Cisco uBR7246. Diplex filters are used to convert the single,
bidirectional signals used by cable modems to the two, separate unidirectional signals used
by the cable modem cards.
List of Terms
— RG-59 headend coaxial cable with the maximum braid available (60% + 40% braid), double
foil, and the correct connector for this cable. The center conductor must be straight and
extend 1/8 inch (3.2 mm) beyond the end of the connector and the connector should be
securely crimped to the cable.
• Complete a basic configuration of the Cisco uBR7246. This includes, as a minimum, the
following tasks:
— Configure a host name and password for the Cisco uBR7246. For more information about
how to configure a host name and password, refer to the Cisco uBR7246 Universal
Broadband Router Installation and Configuration Guide.
— Configure the Cisco uBR7246 to support IP. For more information about how to configure
IP, refer to the refer to the “IP Overview,” “Configuring IP Addressing,” and “Configuring IP
Services” chapters in the Network Protocols Configuration Guide, Part 1.
— Install and configure at least one port adapter to provide WAN connectivity. The
Cisco uBR7246 supports the following port adapters: 4-port 10BASE-T Ethernet, 8-port
10BASE-T Ethernet, 100BASE-T Fast Ethernet, ATM, and HSSI.
For information about installing and configuring the 4-port 10BASE-T port adapter, refer to
the 4-E Ethernet 10BASE-T Port Adapter Installation and Configuration document.
For information about installing and configuring the 8-port 10BASE-T port adapter, refer to
the 8-E Ethernet 10BASE-T Port Adapter Installation and Configuration document.
For information about installing and configuring the 100BASE-T Fast Ethernet port adapter,
refer to the 100BASE-T Fast Ethernet Port Adapter Installation and Configuration
document.
For information about installing and configuring the ATM port adapter, refer to the ATM Port
Adapter Installation and Configuration document.
For information about installing and configuring the HSSI port adapter, refer to the HSSI Port
Adapter Installation and Configuration document.
Configuring Cisco uBR7246 Universal Broadband Router Features VC-137
Configure the Downstream Cable Interface
• Install at least one Cisco MC11 cable modem card in the appropriate slot of Cisco uBR7246
chassis. For information about installing the Cisco MC11 cable modem card, refer to the
Cisco uBR7246 Universal Broadband Router Cable Modem Card Installation and Configuration
document.
Supported MIBs and RFCs
The Cisco uBR7246 universal broadband features support the RF Interface Management
Information Base (MIB). No RFCs are supported by this feature.
Universal Broadband Features Configuration Task List
The Cisco IOS software command-line interface (CLI) is used to configure the Cisco MC11 cable
modem card for correct operation on the HFC network. Perform the following tasks to configure the
MC11 cable modem card. For some tasks, the default values are adequate to configure the device;
these configuration tasks are optional.
• Configure the Downstream Cable Interface (Optional)
• Configure the Upstream Cable Interface
• Configure and Activate Baseline Privacy
• Configure and Activate Frequency Agility
• Activate IP Address Resolution Protocol (Optional)
• Activate Host-to-Host Communication (Proxy ARP) (Optional)
• Set Optional IP Parameters (Optional)
• Manage Cable Modems on the HFC Network (Optional)
Configure the Downstream Cable Interface
The first step in configuring the MC11 cable modem interface is to configure the downstream cable
interface. In this case, downstream refers to the data flow from the Cisco MC11 modem card in a
Cisco uBR7246 to the user’s cable modem. Data passing through the MC11 cable modem card is
converted to IF and then run through an upconverter to transform the signal to RF. This RF signal is
then sent down the line to the user’s cable modem. Downstream cable interface commands configure
the frequency, symbol rate, compression, and modulation of the downstream signal.
Perform the following tasks to configure the downstream cable interface:
• Set the Downstream Center Frequency
• Set the Downstream Symbol Rate
VC-138
• Set the Downstream MPEG Framing Format (Annex A or Annex B)
• Set the Downstream Modulation
• Set the Downstream Interleave Depth
• Activate the Downstream Carrier
Voice, Video, and Home Applications Configuration Guide
Note The default values for the commands used in these configuration steps are, in most cases,
adequate to configure the Cisco uBR7246.
Set the Downstream Center Frequency
You need to set the downstream frequency of your RF output to comply with the expected input
frequency of your upconverter. To do this, enter the fixed center frequency of the downstream RF
carrier for a downstream port.
Downstream frequency is an information-only command that should reflect the digital carrier
frequency, which is the center frequency of the downstream RF carrier (the channel) for that
downstream port. The configuration controlling the digital carrier frequency is done in the IF-to-RF
upconverter that must be installed in the downstream path from the Cisco uBR7246. Refer to the
upconverter’s manufacturer’s instructions for information about configuring the upconverter.
The digital carrier frequency is specified to be the center of a 6.0 MHz channel. For example, EIA
channel 95 spans 90.000 to 96.000 MHz. The center frequency is 93.000 MHz, which is the digital
carrier frequency that should be configured as the downstream frequency.
Note The digital carrier frequency is not the same as the video carrier frequency. For EIA channel
95, the video carrier frequency is 91.250 MHz, which is 1.75 MHz below the center frequency.
Set the Downstream Center Frequency
Validation Tips
Note This command currently has no effect on external upconverters; it is informational only.
To set the downstream center frequency, use the following command in cable interface configuration
mode:
Command Purpose
cable downstream frequency down-freq-hz Enter the fixed center frequency for your downstream
RF carrier in Hz.
To verify the current value of the center frequency, enter the show controllers cable command for
the downstream port that you have just configured:
• If the center frequency is fixed, the actual frequency will be displayed:
router# show controllers cable 6/0 downstream
Cable6/0 Downstream is up
Frequency=96000000, Channel Width 6 MHz, 64-QAM, Symbol Rate 5.056941 Msps
FEC ITU-T J.83 Annex B, R/S Interleave I=32, J=4
• If the center frequency is not fixed, the frequency will show that it is not set:
router# show controllers cable 6/0 downstream
Cable6/0 Downstream is up
Frequency is not set. Channel Width 6 MHz, 64-QAM, Symbol Rate 5.056941 Msps
FEC ITU-T J.83 Annex B, R/S Interleave I=32, J=4
Configuring Cisco uBR7246 Universal Broadband Router Features VC-139
Configure the Downstream Cable Interface
Troubleshooting Tips
If you are having trouble:
• Make sure the cable connections are not loose or disconnected.
• Make sure the cable modem card is firmly seated in its Cisco uBR7246 chassis slot.
• Make sure that you have entered the correct slot and port numbers when you typed the command.
• Make sure you have calculated and entered the center frequency for your headend accurately.
Set the Downstream Symbol Rate
You need to set the megasymbols per second (Msps) rate for a downstream port on a cable modem
card. A symbol is the basic unit of modulation. QPSK encodes 2 bits per symbol, 16-QAM encodes
4 bits per symbol, 64-QAM encodes 6 bits per symbol, and 256-QAM encodes 8 bits per symbol.
The valid range for the downstream symbol rate is 0 to 6,000,000 Msps.
Caution The default downstream symbol rate is set to comply with MCNS specifications for Annex B
cable modem support at 5.056941 Msps with 64-QAM modulation and 5.36037 Msps with 256-QAM
modulation. This command should only be used to change the symbol rate to support Annex A cable modems
that are used outside North America.
To set the downstream symbol rate, use the following command in cable interface configuration
mode:
Command Purpose
cable downstream symbol-rate
Validation Tips
To verify the downstream symbol rate, enter the show controllers cable command for the
downstream port that you have just configured:
Troubleshooting Tips
If you are having trouble:
• Make sure the cable connections are not loose or disconnected.
• Make sure the cable modem card is firmly seated in its Cisco uBR7246 chassis slot.
• Make sure that you have entered the correct slot and port numbers when you typed the command.
number Set the downstream symbol rate for Annex A
(5.056944
symbol rate.
router# show controllers cable 6/0 downstream
Cable6/0 Downstream is up
Frequency=96000000, Channel Width 6 MHz, 64-QAM, Symbol Rate 5.056941 Msps
FEC ITU-T J.83 Annex B, R/S Interleave I=32, J=4
Msps). Do not enter the decimal point in the
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• Make sure you have selected the default if you are using Annex B cable modems.
• Make sure that you have entered the correct symbol rate for Annex A specifications if you are
using Annex A cable modems. Do not enter the decimal point when entering the symbol rate.
• Make sure the downstream carrier is active by entering the cable downstream if-output
command.
Voice, Video, and Home Applications Configuration Guide
Set the Downstream MPEG Framing Format (Annex A or Annex B)
Set the Downstream MPEG Framing Format (Annex A or Annex B)
The MPEG framing format must be compatible with the downstream symbol rate you set. Set the
MPEG framing format for a downstream port on a cable modem card to either Annex A or Annex B.
Annex B is the North America standard and Annex A is the European standard. You should review
your local standards and specifications for downstream MPEG framing to determine which format
you should use.
Note The cable modem card downstream ports and the cable modems on the HFC network
connected through these ports must be set to the same MPEG framing format.
To set the downstream MPEG framing format, use the following command in cable interface
configuration mode:
Command Purpose
cable downstream annex {A | B} Set the downstream MPEG framing format.
Validation Tips
To verify the downstream MPEG framing format (Annex A or Annex B) setting, enter the show
controllers cable command for the downstream port that you have just configured:
router# show controllers cable 6/0 downstream
Cable6/0 Downstream is up
Frequency=96000000, Channel Width 6 MHz, 64-QAM, Symbol Rate 5.056941 Msps
FEC ITU-T J.83 Annex B, R/S Interleave I=32, J=4
Troubleshooting Tips
If you are having trouble:
• Make sure the cable connections are not loose or disconnected.
• Make sure the cable modem card is firmly seated in its Cisco uBR7246 chassis slot.
• Make sure that you have entered the correct slot and port numbers when you typed the command.
• Make sure you have selected the correct setting for your location.
• Make sure the downstream carrier is active by entering the cable downstream if-output
command.
Set the Downstream Modulation
Downstream modulation is the number of symbols per second; by setting the downstream
modulation, you define the speed at which data travels downstream to the user, which is 64 qam
(6 bits per downstream symbol rate).
Note The Cisco cable modem cards currently do not offer a downstream modulation setting for
256-QAM (8 bits per downstream symbol rate).
Configuring Cisco uBR7246 Universal Broadband Router Features VC-141
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