Installation guide

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Cisco uBR7100 Series Universal Broadband Router Software Configuration Guide
OL-2238-03
Chapter 1 Overview
Operating Standards for Cisco IOS Software
Upstream signals are demodulated using quadrature phase shift keying (QPSK) or quadrature amplitude
modulation (QAM). QPSK carries information in the phase of the signal carrier, whereas QAM uses both
phase and amplitude to carry information.
Tip If your cable plant is susceptible to ingress or noise, QPSK is recommended based on the importance of
the data. Frequencies below 20 MHz are more susceptible to noise and might require lower symbol rates.
Higher frequencies might be able to support higher rates and use QAM modulation instead.
Automatic Provisioning of Cable Modems
A key component of DOCSIS networks is the ability to automatically provision each CM or STB as it
comes online. To allow for this, the systems administrator creates DHCP and DOCSIS configuration
files on the appropriate servers such that each CM or CM in an STB on the network, when initialized,
can transmit a DHCP request, receive its IP address, obtain its TFTP and TOD server addresses, and
download its DOCSIS configuration file (and updated software image, if needed).
The automatic provisioning scenario uses the following servers, which must be available to the CM
through the cable interface:
• DHCP server—The CM must contact a DHCP server through the cable interface to obtain its IP
address and other information, such as the default gateway and TFTP server from which to download
its DOCSIS configuration file. If the CM cannot contact the DHCP server, it refuses to come online
and restarts the registration process.
• TFTP server—The CM must download its DOCSIS configuration file from a TFTP server (as
specified in RFC 1350) that is accessible through the cable interface. If the CM cannot download
the DOCSIS configuration file, it refuses to come online and restarts the registration process. The
TFTP server can be a separate workstation (such as a Unix or Windows NT computer), or the
Cisco uBR7100 series router can also operate as a TFTP server for smaller installations.
Using information in the DOCSIS configuration file, the CM can also use the TFTP server to
download an updated software image or another configuration file (such as a Cisco IOS
configuration file).
Note Most Unix-based systems include a TFTP server but it must be enabled by modifying the
inetd.conf file. TFTP server for the Microsoft Windows NT and 2000 operating systems might
be part of the operating system, depending on how it was installed, or a TFTP server can be
downloaded from ftp.cisco.com.
• ToD server—The CM automatically attempts to connect to a ToD server (as specified in RFC 868)
to obtain the current time so it can accurately timestamp its log and other messages. However, this
server is optional, and if the CM cannot connect to the ToD server within a specified number of
retries, the CM will abandon the attempt and continue with the provisioning process.
Note A TOD server is typically embedded in systems using the Unix operating system and is
automatically enabled through the inetd utility. Microsoft Windows NT and 2000 do not include
a ToD server, but public domain versions of this software are available for download several sites
on the Internet.
• Log server—The CM can be optionally configured to send system log messages to a SYSLOG
server. This is useful but not required for DOCSIS operations.