The downstream peak
traffic rate TLV (DOCSIS 3.0 TLV 25.27) support for the ERBA feature was
introduced in Cisco IOS Release 12.2(33)SCB1 for the Cisco uBR10012 router.
This feature support was extended to Cisco uBR7246VXR and Cisco uBR7225VXR
routers in Cisco IOS Release 12.2(33)SCD.
The DOCSIS WFQ
Scheduler allows each service flow to have one dedicated queue. When ERBA is
enabled for the service flow, the peak rate is implemented as the queue shape
rate within the scheduler, while the maximum sustained rate is set as the token
bucket refill rate. When ERBA is turned off, the burst size and the peak rate
value are not used.
The maximum traffic
burst parameter is used to control a service flow burst duration, to burst up
to the channel line rate or a configured peak rate, when it is within its
maximum burst size allowance. On the Cisco uBR10012 Universal Broadband Router,
the
cable
ds-max-burst command is used to control this
behavior explicitly.
In Cisco IOS
Release 12.2(33)SCB1, the
peak-rate
keyword was introduced to specify the peak rate an ERBA-enabled service flow
can use. The peak rate value is a global value and is applied to all service
flows created after the configuration of the
cable
ds-max-burst
command.
If the DOCSIS 3.0
TLV 25.27 is specified for a service flow, the
peak rate
value is set as the TLV value. However, if ERBA is not turned on for
a service flow, the
peak rate
value is ignored.
The
peak rate
value can also be configured using the cable service class command,
which forms part of the service class template. During modem registration or
Dynamic Service Addition (DSA) operation, the service class name TLV 25.4 is
sent to create the static or dynamic downstream service flow that matches the
service class template. These downstream service flows are created with a
specific
peak rate . If
the
peak rate
is not specified, then the value specified by the
cable
ds-max-burst command is used.
If a service flow
has both service class and TLV 25.27 defined
peak rate ,
then the
peak rate
value specified in the TLV is used.
Some of the DOCSIS
1.x an DOCSIS 2.0 cable modems, which are not fully DOCSIS 1.x or DOCSIS 2.0
compliant, may fail to come online when the downstream peak rate TLV 25.27 is
received from the CMTS during registration. To overcome this failure, you can
configure the cable service attribute withhold-TLVs command to restrict sending
of the peak traffic rate TLVs to DOCSIS1.x and DOCSIS 2.0 cable modems. For
more information on how to suppress peak rate TLVs, see
Suppressing Upstream and Downstream Peak Rate TLVs for pre DOCSIS 3.0 Cable Modems.
 Note |
The ERBA feature
is not applicable for high priority service flows and multicast service flows.
|
Table below
summarizes the ERBA support for the Cisco uBR10012 router.
Table 2 Enhanced Rate
Bandwidth Allocation Support for the Cisco uBR10012 Router
|
Policer
Rate
|
Policer
Exceed Action
|
Policer
Token Bucket Size
|
Queue Shape
Rate
|
Traditional
Service Flow
|
Maximum
Sustained Traffic Rate (unused)
|
Transmit
|
A value
computed internally by CMTS (unused)
|
Maximum
Sustained Traffic Rate
|
ERBA-Enabled Service Flow
|
Maximum
Sustained Traffic Rate
|
Drop
|
Maximum
Traffic Burst TLV
|
Peak
Traffic Rate
|
In Cisco uBR7246VXR
and Cisco uBR7225VXR routers, the dual token bucket-based shaper is used to
support ERBA on the Cisco uBR-MC88V line card (the ERBA feature is always
enabled on the Cisco uBR-MC88V line card). The dual token bucket shaper has two
independent token buckets for each service flow. The maximum rate of one bucket
is configured to MSR and the maximum tokens are set to maximum traffic burst.
The other bucket is configured with the refilling rate of the
peak rate
and the maximum tokens are set to the default level of 4
milliseconds. Packets are shaped if any of the two buckets are exhausted.
Table below
summarizes the ERBA dual token bucket configuration for the Cisco uBR7246VXR
and Cisco uBR7225VXR routers.
Table 3 ERBA Dual Token
Bucket Configuration
|
Token
Bucket Rate (One)
|
Token
Bucket Size (One)
|
Token
Bucket Rate (Two)
|
Token
Bucket Size (Two)
|
Traditional
Service Flow
|
Maximum
Sustained Traffic Rate
|
4ms * MSR
|
N/A
|
N/A
|
ERBA-enabled Service Flow
|
Maximum
Sustained Traffic Rate
|
Maximum
Traffic Burst or 4ms * MSR
|
Peak Rate
|
4ms *
Peak Rate
|
 Note |
The
cable
ds-max-burst command is not supported on the Cisco
uBR7246VXR and Cisco uBR7225VXR routers.
|