Cisco Cisco IOS Software Release 12.1(7)CX
Restrictions
16
DOCSIS 1.1 for Cisco uBR7200 Series Universal Broadband Routers
Cisco IOS Release 12.1(7)CX1
If a cable modem attempts to register with a maximum concatenation burst size of zero, the DOCSIS 1.1
CMTS will refuse to allow the cable modem to come online. This avoids the possibility that a
DOCSIS 1.0 cable modem could interfere with voice traffic on the upstream by sending extremely large
data packets. Since DOCSIS 1.0 does not support fragmentation, transmitting such data packets could
result in unwanted jitter in the voice traffic.
CMTS will refuse to allow the cable modem to come online. This avoids the possibility that a
DOCSIS 1.0 cable modem could interfere with voice traffic on the upstream by sending extremely large
data packets. Since DOCSIS 1.0 does not support fragmentation, transmitting such data packets could
result in unwanted jitter in the voice traffic.
In addition, DOCSIS 1.1 requires that the maximum transmit burst size be set to either 1522 bytes or the
maximum concatenated burst size, whichever is larger. Do not set the maximum concatenation burst size
to values larger than 1522 bytes for DOCSIS 1.0 cable modems.
maximum concatenated burst size, whichever is larger. Do not set the maximum concatenation burst size
to values larger than 1522 bytes for DOCSIS 1.0 cable modems.
Note
This change requires you to change any DOCSIS configuration files that specify a zero value for the
maximum concatenation burst size. This limitation does not exist for DOCSIS 1.1 cable modems
unless fragmentation has been disabled.
maximum concatenation burst size. This limitation does not exist for DOCSIS 1.1 cable modems
unless fragmentation has been disabled.
Provisioning
The format and content of the TFTP configuration file for a DOCSIS 1.1 cable modem are significantly
different from the file for a DOCSIS 1.0 cable modem. A dual-mode configuration file editor is used to
generate a DOCSIS 1.0 style configuration file for DOCSIS 1.0 cable modems and a DOCSIS 1.1
configuration file for DOCSIS 1.1 cable modems.
different from the file for a DOCSIS 1.0 cable modem. A dual-mode configuration file editor is used to
generate a DOCSIS 1.0 style configuration file for DOCSIS 1.0 cable modems and a DOCSIS 1.1
configuration file for DOCSIS 1.1 cable modems.
Registration
A DOCSIS 1.1 CMTS is designed to handle the existing registration TLVs from DOCSIS 1.0 cable
modems as well as the new type TLVs from DOCSIS 1.1 cable modems. A DOCSIS 1.0 and DOCSIS 1.1
cable modem can successfully register with the same DOCSIS 1.1 CMTS.
modems as well as the new type TLVs from DOCSIS 1.1 cable modems. A DOCSIS 1.0 and DOCSIS 1.1
cable modem can successfully register with the same DOCSIS 1.1 CMTS.
A DOCSIS 1.1 cable modem can be configured to make an indirect reference to a service class that has
been statically defined at the CMTS instead of explicitly asking for the service class parameters. When
this registration request is received by a DOCSIS 1.1 CMTS, it encodes the actual parameters of the
service class in the registration response and expects a DOCSIS 1.1-specific registration-acknowledge
MAC message from the cable modem.
been statically defined at the CMTS instead of explicitly asking for the service class parameters. When
this registration request is received by a DOCSIS 1.1 CMTS, it encodes the actual parameters of the
service class in the registration response and expects a DOCSIS 1.1-specific registration-acknowledge
MAC message from the cable modem.
When a DOCSIS 1.0 cable modem registers with a DOCSIS 1.1 CMTS, the registration request
explicitly requests all nondefault service-class parameters in the registration. The absence of an indirect
service class reference eliminates the need for the DOCSIS 1.1 TLVs and eliminates the need to establish
a local registration acknowledge wait state.
explicitly requests all nondefault service-class parameters in the registration. The absence of an indirect
service class reference eliminates the need for the DOCSIS 1.1 TLVs and eliminates the need to establish
a local registration acknowledge wait state.
When a DOCSIS 1.1 CMTS receives a registration request from a DOCSIS 1.0 cable modem, it responds
with the DOCSIS 1.0 style registration response and does not expect the cable modem to send the
registration-acknowledge MAC message.
with the DOCSIS 1.0 style registration response and does not expect the cable modem to send the
registration-acknowledge MAC message.
Performance
DOCSIS 1.0 cable modems lack the ability to explicitly request and provide scheduling parameters for
advanced DOCSIS 1.1 scheduling mechanisms, such as unsolicited grants and real-time polling.
DOCSIS 1.1 cable modems on the same upstream channel can benefit from the advanced scheduling
mechanisms and a DOCSIS 1.1 CMTS can still adequately support voice traffic from DOCSIS 1.1 cable
modems with DOCSIS 1.0 cable modems on the same upstream channel.
advanced DOCSIS 1.1 scheduling mechanisms, such as unsolicited grants and real-time polling.
DOCSIS 1.1 cable modems on the same upstream channel can benefit from the advanced scheduling
mechanisms and a DOCSIS 1.1 CMTS can still adequately support voice traffic from DOCSIS 1.1 cable
modems with DOCSIS 1.0 cable modems on the same upstream channel.