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This document describes the Service Group Admission Control feature.
Your software release may not support all the features documented in this module. For the latest caveats and feature information, see Bug Search Tool and the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the feature information table.
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Note | The hardware components introduced in a given Cisco IOS-XE Release are supported in all subsequent releases unless otherwise specified. |
Service Group Admission Control (SGAC) is a mechanism that gracefully manages service group based admission requests when one or more resources are not available to process and support the incoming service request. Lack of such a mechanism not only causes the new request to fail with unexpected behavior but could potentially cause the flows that are in progress to have quality related problems. SGAC monitors such resources constantly, and accepts or denies requests based on resource availability.
SGAC enables you to provide a reasonable guarantee about the Quality of Service (QoS) to subscribers at the time of call admission, and to enable graceful degradation of services when resource consumption approaches critical levels. SGAC reduces the impact of unpredictable traffic demands in circumstances that would otherwise produce degraded QoS for subscribers.
Note | SGAC begins graceful degradation of service when either a critical threshold is crossed, or when bandwidth is nearly consumed on the Cisco CMTS, depending on the resource being monitored. |
SGAC enables you to configure thresholds for each resource on the Cisco CMTS. These thresholds are expressed in a percentage of maximum allowable resource utilization. Alarm traps may be sent each time a threshold is crossed for a given resource.
For downstream (DS) channels, you can configure the bandwidth allocation with thresholds for each fiber node.
SGAC allows you to control the bandwidth usage for various DOCSIS traffic types or application types. The application types are defined by the user using a CLI to categorize the service flow.
The SGAC feature allows you to allocate the bandwidth based on the application types. Flow categorization allows you to partition bandwidth in up to eight application types or buckets. The composition of a bucket is defined by the command-line interface (CLI), as is the definition of rules to categorize service flows into one of these eight application buckets. Various attributes of the service flow may be used to define the rules.
For flows created by PacketCable, the following attributes may be used:
For flows created by PacketCable MultiMedia (PCMM), the following attributes may be used:
All flows use the following attribute type:
Before a service flow is admitted, it is passed through the categorization routine. Various attributes of the service flow are compared with the user-configured rules. Based on the match, the service flow is labeled with application type, from 1 to 8. The bandwidth allocation is then performed per application type.
Before a service flow is admitted, it is categorized based on its attributes. The flow attributes are compared against CLI-configured rules, one bucket at a time. If a match is found for any one of the rules, the service flow is labeled for that bucket, and no further check is performed.
Bucket 1 rules are scanned first and bucket 8 rules are scanned last. If two different rules match two different buckets for the same service flow, the flow gets categorized under the first match. If no match is found, the flow is categorized as Best Effort (BE) and the bucket with best effort rule is labelled to the flow. By default, the BE bucket is bucket 8.
SGAC monitors downstream bandwidth consumption using the configured maximum reserved bandwidth. It rejects service flows with a non-zero minimal rate that would make the total reserved bandwidth exceed the configured threshold.
To address the issue of restricted bandwidth allocation for different application types, admission control can be applied for both normal priority and emergency voice flows. This is done by extending the threshold and assigning a group of application types in a fiber node. Each downstream service flow continues to be categorized for a single application type. However, the one-to-one mapping between an application type and a threshold no longer exists.
Each configured threshold and its associated group of application types can thus be treated as a constraint. A service flow categorized to a certain application type must pass all the constraints associated with that application type.
DOCSIS 3.0 introduced bonded channels or bonding groups that allow a single cable modem to send data over multiple RF channels achieving higher throughput. These bonding groups are defined for both upstream and downstream channels. Bonding groups are created by combining multiple RF channels. A single RF channel may also be shared by multiple bonding groups.
Note | Effective from Cisco IOS-XE 3.18.0SP Release, as per DOCSIS 3.1, if bonding group contains an OFDM channel, the bonding group's total bandwidth that can be reserved (its capacity), is calculated using the least efficient OFDM profile it can use. |
Bonding group SGAC functionality allows to define the maximum reserved bandwidth for an application-type as a fraction of the available bandwidth. This fraction of the bandwidth is defined as a percentage value of the total bandwidth that can be reserved.
Configuration procedures are optional because the default configurations are enabled by default. This section presents a sequence of procedures for non-default configurations, monitoring and debugging procedures for both the default or non-default operations of SGAC.
This procedure describes how to configure service flow categorization rules on the Cisco CMTS. This flexible procedure changes default global service flow rules with variations of the cable application type include command.
Any one or several of these steps or commands may be used, in nearly any combination, to set or re-configure SGAC on the Cisco CMTS.
Note | Application rules for SGAC are global configurations, and downstream bandwidth resources use the same sets of service flow rules. |
The following example maps high-priority PacketCable service flows into application bucket 5.
Router(config)# cable application-type 5 include packetcable priority
The following example maps normal PacketCable service flows into application bucket 1.
Router(config)# cable application-type 1 include packetcable normal
The following example maps the specified bucket number with PCMM service flow with a priority of 7, then maps an application identifier of 152 for the same bucket number:
Router(config)# cable application-type 2 include pcmm priority 7 Router(config)# cable application-type 2 include pcmm app-id 152
The following example maps the Best Effort CIR flows to bucket 3:
Router(config)# cable application-type 3 include BE
This procedure enables you to assign alpha-numeric names to six of the eight application buckets that SGAC supports. The default bucket identifiers range from 1 to 8.
You may configure SGAC rules and thresholds so that the high-priority voice (911) traffic receives an exclusive share of bandwidth. Because the average call volume for Emergency 911 traffic may not be very high, the fraction of bandwidth reserved for Emergency 911 calls may be small. In the case of regional emergency, the call volume of Emergency 911 calls may surge. In this case, it may be necessary to preempt some of the normal voice traffic to make room for surging Emergency 911 calls.
The Cisco CMTS software preempts one or more normal-priority voice flows to make room for the high-priority voice flows. SGAC provides the command-line interface (CLI) to enable or disable this preemption ability.
SGAC preemption logic follows the following steps:
This preemption is effective only for PacketCable high-priority flows.
When a downstream low-priority service flow is chosen for preemption, the corresponding service flow for the same voice call in the opposite direction gets preempted as well.
Command or Action | Purpose | |
---|---|---|
Step 1 | enable
Example: Router> enable |
Enables privileged EXEC mode. |
Step 2 | configure
terminal
Example: Router# configure terminal |
Enters global configuration mode.
|
Step 3 | [
no ]
cable
admission-control
preempt
priority-voice
Example: Router(config)# no cable admission-control preempt priority-voice |
Changes the default Emergency 911 call preemption functions on the Cisco CMTS, supporting throughput and bandwidth requirements for Emergency 911 calls above all other buckets on the Cisco CMTS. The no form of this command disables this preemption, and returns the bucket that supports Emergency 911 calls to default configuration and normal function on the Cisco CMTS.
|
Step 4 |
Ctrl-Z
Example: Router(config)# Ctrl^Z Router# |
Returns to Privileged EXEC mode. |
The SGAC feature maintains a counter for every US and DS channel, and this counter stores the current bandwidth reservation. Whenever a service request is made to create a new service flow, SGAC estimates the bandwidth needed for the new flow, and adds it to the counter. The estimated bandwidth is computed as follows:
In each of the above calculations, SGAC does not account for the PHY overhead. DOCSIS overhead is counted only in the UGS and UGS-AD flows. To estimate the fraction of bandwidth available, the calculation must account for the PHY and DOCSIS overhead, and also the overhead incurred to schedule DOCSIS maintenance messages. SGAC applies a correction factor of 80% to the raw data rate to calculate the total available bandwidth.
Note | For the DS and US flow in bonded channels, the maximum reserved bandwidth is the bandwidth defined for the SGAC threshold values. This value is indicated in kbps. |
A fiber node configured on the CMTS represents one or more matching physical fiber nodes in the HFC plant. The CMTS uses the fiber node configuration to identify the DOCSIS downstream service group (DS-SG) and DOCSIS upstream Service Group (US-SG) of the physical fiber nodes in the plant. The Service Group information is compared with MAC Domain channel configuration to automatically calculate the MAC Domain downstream and upstream service groups (MD-DS-SGs and MD-US-SGs respectively) within the MAC Domains.
Under each Fiber node, use the following procedure to enable SGAC check for an application type and any service flow of the specified application type, which is admitted to a service group.
Fairness Across DOCSIS Interfaces feature should always be enabled and the bandwidth percentage configured on each bonding group should be kept minimal to allow flexible adjustment of reservable bandwidth.
Restrictions
SGAC is supported only on the downstream.
Command or Action | Purpose | |
---|---|---|
Step 1 | enable
Example: Router> enable |
Enables privileged EXEC mode. |
Step 2 | configureterminal
Example: Router# configure terminal |
Enters global configuration mode. |
Step 3 |
cable fiber-node
id
Example: Router(config)# cable fiber-node 1 |
Enters cable fiber-node configuration mode to configure a fiber node. |
Step 4 |
admission-control application-type
n
ds-bandwidth
pct
Example: Router(config-fiber-node)# admission-control application-type 1 ds-bandwidth 1 |
Enables SGAC checking for the specified application-type. Use the no form of this command to disable SGAC checking. |
Step 5 |
Ctrl-Z
Example: Router(config-if)# Ctrl^Z |
Returns to Privileged EXEC mode. |
Use the show cable admission-control fiber-node n command to verify admission-control configuration.
This section describes solutions-level examples of the SGAC feature on the Cisco CMTS. This section illustrates the functioning of SGAC in default or non-default operational configurations.
In this section of configuration examples, the following SGAC parameters are set on the Cisco CMTS:
The following configuration commands enable these settings:
cable application-type 1 include packetcable normal cable application-type 1 include packetcable priority cable application-type 1 name PktCable
cable application-type 8 name HSD cable application-type 8 include best-effort
cable application-type 2 name PCMM-Vid cable application-type 2 include pcmm app-id 35
Router# show cable application-type For bucket 1, Name PktCable Packetcable normal priority gates Packetcable high priority gates For bucket 2, Name PCMM-Vid PCMM gate app-id = 30 For bucket 3, Name Gaming PCMM gate app-id = 40 For bucket 4, Name For bucket 5, Name For bucket 6, Name For bucket 7, Name For bucket 8, Name HSD Best-effort (CIR) flows
Router# show cable admission-control fiber-node 1 App-type Name Exclusive 1 N/A 2 N/A 3 Normal 10% 4 N/A 5 N/A 6 N/A 7 Emergency N/A 8 N/A
Router#show cable admission-control interface integrated-Cable 8/0/0:0 Interface In8/0/0:0 RFID 24576 Resource - Downstream Bandwidth ------------------------------- App-type Name Reservation/bps Exclusive Rejected 1 0 N/A 0 2 0 N/A 0 3 Normal 0 10% 0 4 0 N/A 0 5 0 N/A 0 6 0 N/A 0 7 Emergency 0 N/A 0 8 0 N/A 0 Max Reserved BW = 300000 bps Total Current Reservation = 0 bps Guaranteed Bonus BW = 21055000 bps Non-guaranteed Bonus BW = 7744000 bps Superset BGs: Wi8/0/0:0 Wi8/0/0:4 Wi8/0/0:6 Router#show cable admission-control interface wideband-Cable 8/0/0:0 Interface Wi8/0/0:0 BGID: 24577 Resource - Downstream Bandwidth ------------------------------- App-type Name Reservation/bps Exclusive Rejected 1 0 N/A 0 2 0 N/A 0 3 Normal 0 10% 0 4 0 N/A 0 5 0 N/A 0 6 0 N/A 0 7 Emergency 0 N/A 0 8 0 N/A 0 Max Reserved BW = 600000 bps Total Current Reservation = 0 bps Guaranteed Bonus BW = 21055000 bps Non-guaranteed Bonus BW = 36844000 bps Subset BGs: In8/0/0:0 In8/0/0:1 Superset BGs: Wi8/0/0:4 Wi8/0/0:6 Overlapping BGs: N/A
These above configuration examples might be omitted or changed, but the remaining examples in this section presume the above configurations.
The below example illustrates a sample configuration for SGAC with downstream traffic. In this example, if voice traffic exceeds 30% bandwidth consumption, additional voice flows are denied.
The following command implements this configuration:
Router(config-fiber-node)#admission-control application-type 1 ds-bandwidth 30
The below example illustrates how flexible bandwidth allocation is configured. In this example, normal voice traffic (application-type 1) is associated with two thresholds. Normal voice traffic alone can use up to 40% of the service group's capacity, while normal and emergency voice traffic combined can use up to 50% of the service group’s capacity. This means that emergency voice traffic can have at least 10% of the service group's capacity, even if normal voice traffic has used up its share of 40%:
Router(config-fiber-node)#admission-control application-type 1 ds-bandwidth 40 Router(config-fiber-node)#admission-control application-type 1-2 ds-bandwidth 50
The following topics provide references related to SGAC for the Cisco CMTS.
Related Topic |
Document Title |
---|---|
Cisco CMTS Cable Commands |
Standard |
Title |
---|---|
CableLabs™ DOCSIS 1.1 specifications |
|
CableLabs™ PacketCable specifications |
|
CableLabs™ PacketCable MultiMedia specifications |
http://www.cablelabs.com/packetcable/specifications/multimedia.html |
MIB |
MIBs Link |
---|---|
MIBs |
To locate and download MIBs for selected platforms, use Cisco MIB Locator found at the following URL: |
Description |
Link |
---|---|
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Note | The table below lists only the software release that introduced support for a given feature in a given software release train. Unless noted otherwise, subsequent releases of that software release train also support that feature. |
Feature Name |
Releases |
Feature Information |
---|---|---|
Flexible Bandwidth Allocation |
Cisco IOS-XE Release 3.17.0S |
This feature was introduced on the Cisco cBR Series Converged Broadband Routers. |
Service Group Admission Control |
Cisco IOS-XE Release 3.16.0S |
This feature was introduced on the Cisco cBR Series Converged Broadband Routers. |