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 cBR-8 Converged Broadband Router,
the
cable
ds-max-burst command is used to control this
behavior explicitly.
The
peak-rate
keyword is introduced to specify the peak rate an ERBA-enabled service flow can
use. The peak rate value is applied to a specific service flow 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.
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.
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 cBR-8 router.
Table 3. Enhanced Rate
Bandwidth Allocation Support for the Cisco cBR-8 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 cBR-8
routers, the dual token bucket-based shaper is used to support ERBA on the
Cisco cBR-8 CCAP line card (the ERBA feature is always enabled on the Cisco
cBR-8 CCAP 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 cBR-8
routers.
Table 4. 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
|