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The MQC Traffic Shaping Overhead Accounting for ATM feature enables a broadband aggregation system (BRAS) to account for various encapsulation types when applying quality of service (QoS) functionality to packets. Typically, in Ethernet digital subscriber line (DSL) environments, the encapsulation from the router to the digital subscriber line access multiplexer (DSLAM) is Gigabit Ethernet and the encapsulation from the DSLAM to the customer premises equipment (CPE) is ATM. ATM overhead accounting enables the router to account for ATM encapsulation on the subscriber line and for the overhead added by cell segmentation. This functionality enables the service provider to prevent overruns at the subscriber line and ensures that the router executes QoS features on the actual bandwidth used by ATM packets.
Your Cisco IOS software release may not support all of the features documented in this module. For the latest feature information and caveats, see the release notes for your platform and software release. To reach links to specific feature documentation in this module and to see a list of the releases in which each feature is supported, use the Feature Information for MQC Traffic Shaping Overhead Accounting for ATM.
Use Cisco Feature Navigator to find information about platform support and Cisco IOS and Catalyst OS software image support. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn . An account on Cisco.com is not required.
Your software release may not support all the features documented in this module. For the latest feature information and caveats, see 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 at the end of this document.
Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.
Traffic classes must be configured using the class-map command.
Note |
This restriction applies to the Cisco 10000 series router only. This restriction does not apply to the Cisco 7600 series router. |
The Traffic Shaping Overhead Accounting for ATM feature enables the broadband aggregation system (BRAS) to account for various encapsulation types when applying QoS to packets. Typically, in Ethernet digital subscriber line (DSL) environments, the encapsulation from the BRAS to the DSLAM is Gigabit Ethernet and the encapsulation from the DSLAM to the CPE is ATM. ATM overhead accounting enables the BRAS to account for ATM encapsulation on the subscriber line and for the overhead added by cell segmentation. This functionality enables the service provider to prevent overruns at the subscriber line and ensures that the router executes QoS features on the actual bandwidth used by ATM subscriber traffic.
Broadband aggregation system (BRAS) uses the encapsulation type that is configured for the DSLAM-CPE side to calculate the ATM overhead per packet.
DSLAM-CPE encapsulation types are based on Subnetwork Access Protocol (SNAP) and multiplexer (MUX) formats of ATM adaptation layer 5 (AAL5), followed by routed bridge (RBE), x-1483, x-dot1q-rbe, IP, PPP over Ethernet (PPPoE), or PPP over ATM (PPPoA) encapsulations. Because the DSLAM treats IP and PPPoE packets as payload, the BRAS does not account for IP and PPPoE encapsulations.
On the BRAS-DSLAM side, encapsulation is IEEE 802.1Q VLAN or Q-in-Q (qinq). However, because the DSLAM removes the BRAS-DSLAM encapsulation, the BRAS does not account for 802.1Q or qinq encapsulation.
AAL5 segmentation processing adds the additional overhead of the 5-byte cell headers, the AAL5 Common Part Convergence Sublayer (CPCS) padding, and the AAL5 trailer. For more information, see the ATM Overhead Calculation.
The router supports the following subscriber line encapsulation types:
Note |
The encapsulation types listed above are for AAL5, qinq, and dot1q encapsulations. User-defined encapsulations with offsets based on the platform in use are also supported. (For the Cisco 10000 series router, valid offsets are -63 to +63. For the Cisco 7600 series router, valid offsets are -48 to +48.) |
The Traffic Shaping Overhead Accounting for ATM feature prevents oversubscription of a subscriber line by accounting for the ATM encapsulation overhead at the BRAS. When calculating the ATM overhead, the Traffic Shaping Overhead Accounting for ATM feature considers the following:
The offset size (a parameter used to calculate ATM overhead accounting) is calculated using the following formula:
Offset size in bytes = (CPCS trailer overhead) + (DSLAM to CPE) - (BRAS encapsulation type)
This offset size, along with the packet size and packet assembler/disassembler (PAD) byte overhead in the CPCS, is used by the router to calculate the ATM overhead accounting rate.
Note |
A CPCS trailer overhead of 8 bytes corresponds to AAL5. A CPCS trailer overhead of 4 bytes corresponds to AAL3, but AAL3 is not supported. |
Table 1 | Offset Sizes, in Bytes, Used for ATM Overhead Calculation |
Encapsulation Type in Use |
BRAS |
CPCS Trailer Overhead |
DSLAM to CPE |
Offset Size |
---|---|---|---|---|
dot1q mux-1483routed |
18 |
8 |
3 |
-7 |
dot1q snap-1483routed |
18 |
8 |
6 |
-4 |
dot1q mux-rbe |
18 |
8 |
14 |
4 |
dot1q snap-rbe |
18 |
8 |
24 |
14 |
dot1q mux-dot1q-rbe |
18 |
8 |
18 |
8 |
dot1q snap-dot1q-rbe |
18 |
8 |
28 |
18 |
qot1q mux-pppoa |
18 + 6 |
8 |
2 |
-14 |
qot1q snap-pppoa |
18 + 6 |
8 |
4 |
-12 |
qinq mux-1483routed |
22 |
8 |
3 |
-11 |
qinq snap-1483routed |
22 |
8 |
6 |
-8 |
qinq mux-rbe |
22 |
8 |
14 |
0 |
qinq snap-rbe |
22 |
8 |
24 |
10 |
qinq mux-dot1q-rbe |
22 |
8 |
18 |
4 |
qing snap-dot1q-rbe |
22 |
8 |
28 |
14 |
qinq mux-pppoa |
22 + 6 |
8 |
2 |
-18 |
qinq snap-pppoa |
22 + 6 |
8 |
4 |
-16 |
In hierarchical policies, you can enable ATM overhead accounting for shaping and bandwidth on parent policies and child policies. You are not required to enable ATM overhead accounting on a traffic class that does not contain the bandwidth or shape command. If you enable ATM overhead accounting on a child policy, then you must enable ATM overhead accounting on the parent policy. The parent and child classes must specify the same encapsulation type when ATM overhead accounting is enabled.
Command or Action | Purpose | |||||
---|---|---|---|---|---|---|
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Example: Router> enable |
Enables privileged EXEC mode. |
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Example: Router# configure terminal |
Enters global configuration mode. |
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Example: Router(config)# policy-map Business |
Creates or modifies the child policy and enters policy-map configuration mode. |
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Example: Router(config-pmap)# class video |
Assigns the traffic class that you specify for the policy map and enters policy-map class configuration mode. |
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Example: Router(config-pmap-c)# bandwidth 8000 account dot1q aal5 snap-pppoa |
Enables Class-Based Weighted Fair Queuing (CBWFQ) on the basis of the keywords and arguments specified, such as the following:
|
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Example: Router(config-pmap-c)# bandwidth remaining ratio 10 account dot1q aal5 snap-pppo |
(Optional) Specifies the bandwidth-remaining ratio for the subinterface along with ATM accounting parameters:
|
||||
|
Example: Router(config-pmap-c)# shape 8000 account qinq aal5 snap-dot1q-rbe |
Shapes traffic to the indicated bit rate and enables ATM overhead accounting on the basis of the keywords and arguments specified, such as the following:
|
||||
|
Example: Router(config-pmap-c)# end |
Exits policy-map class configuration mode. |
In the following example, overhead accounting is enabled for bandwidth on the gaming and class-default class of the child policy map named subscriber_classes and on the class-default class of the parent policy map named subscriber_line. The voip and video classes do not have accounting explicitly enabled; these classes have ATM overhead accounting implicitly enabled because the parent policy has overhead accounting enabled. Notice that the features in the parent and child policies use the same encapsulation type.
policy-map subscriber_classes class voip priority level 1 police 8000 class video priority level 2 police 8000 class gaming bandwidth remaining percent 80 accountaal5 snap-rbe-dot1q class class-default bandwidth remaining percent 20 accountaal5 snap-rbe-dot1q policy-map subscriber_line class class-default bandwidth remaining ratio 10 accountaal5 snap-rbe-dot1q shape average 512 account aal5snap-rbe-dot1q service policy subscriber_classes
Router# show policy-map interface
Router# show policy-map session output
SSS session identifier 2 -
Service-policy output: ATM_OH_POLICY
Class-map: class-default (match-any)
0 packets, 0 bytes
30 second offered rate 0 bps, drop rate 0 bps
Match: any
Queueing
queue limit 2500 packets
(queue depth/total drops/no-buffer drops) 0/0/0
(pkts output/bytes output) 0/0
shape (average) cir 10000000, bc 40000, be 40000
target shape rate 10000000
Overhead Accounting Enabled
The following output from the show running-config command indicates that ATM overhead accounting is enabled for shaping. The BRAS-DSLAM encapsulation is dot1q and the subscriber line encapsulation is snap-rbe based on the AAL5 service.
subscriber policy recording rules limit 64 no mpls traffic-eng auto-bw timers frequency 0 call rsvp-sync ! controller T1 2/0 framing sf linecode ami ! controller T1 2/1 framing sf linecode ami ! ! policy-map unit-test class class-default shape average percent 10 account dot1q aal5 snap-rbe !
The following sections provide references related to traffic shaping overhead accounting for ATM.
Related Topic |
Document Title |
---|---|
QoS commands: complete command syntax, command modes, command history, defaults, usage guidelines, and examples |
Cisco IOS Quality of Service Solutions Command Reference |
Modular Quality of Service (QoS) Command-Line Interface (CLI) (MQC), hierarchical policies, policy maps |
"Applying QoS Features Using the MQC" module |
Policing and shaping traffic |
"Policing and Shaping Overview" module |
Standard |
Title |
---|---|
No new or modified standards are supported by this feature, and support for existing standards has not been modified by this feature. |
-- |
MIB |
MIBs Link |
---|---|
No new or modified MIBs are supported by this feature, and support for existing MIBs has not been modified by this feature. |
To locate and download MIBs for selected platforms, Cisco IOS releases, and feature sets, use Cisco MIB Locator found at the following URL: |
RFC |
Title |
---|---|
No new or modified RFCs are supported by this feature, and support for existing RFCs has not been modified by this feature. |
-- |
Description |
Link |
---|---|
The Cisco Support and Documentation website provides online resources to download documentation, software, and tools. Use these resources to install and configure the software and to troubleshoot and resolve technical issues with Cisco products and technologies. Access to most tools on the Cisco Support and Documentation website requires a Cisco.com user ID and password. |
The following commands are introduced or modified in the feature or features documented in this module. For information about these commands, see the Cisco IOS Quality of Service Solutions Command Reference. For information about all Cisco IOS commands, use the Command Lookup Tool at http://tools.cisco.com/Support/CLILookup or a Cisco IOS master commands list.
The following table provides release information about the feature or features described in this module. This table 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.
Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.
Table 2 | Feature Information for MQC Traffic Shaping Overhead Accounting for ATM |
Feature Name |
Releases |
Feature Information |
---|---|---|
MQC Traffic Shaping Overhead Accounting for ATM |
12.2(31)SB2 12.2(33)SRC 12.2(33)SB |
The MQC Traffic Shaping Overhead Accounting for ATM feature enables a broadband aggregation system (BRAS) to account for various encapsulation types when applying QoS functionality to packets. In Release 12.2(31)SB2, this feature was introduced and implemented on the Cisco 10000 series router for the PRE3. In Release 12.2(33)SRC, support was added for the Cisco 7600 series router. In Release 12.2(33)SB, support was added for the Cisco 7300 series router. The following commands were introduced or modified: bandwidth (policy-map class), bandwidth remaining ratio, shape (policy-map class), show policy-map interface, show policy-map session, show running-config. |
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