MQC Traffic Shaping Overhead Accounting for ATM
First Published: December 4, 2006
Last Updated: March 23, 2011
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.
Finding Feature Information
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 for MQC Traffic Shaping Overhead Accounting for ATM" section.
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Contents
•Prerequisites for Traffic Shaping Overhead Accounting for ATM
•Restrictions for Traffic Shaping Overhead Accounting for ATM
•Information About Traffic Shaping Overhead Accounting for ATM
•How to Configure Traffic Shaping Overhead Accounting for ATM
•Configuration Examples for Traffic Shaping Overhead Accounting for ATM
•Additional References
•Feature Information for MQC Traffic Shaping Overhead Accounting for ATM
Prerequisites for Traffic Shaping Overhead Accounting for ATM
Traffic classes must be configured using the class-map command.
Restrictions for Traffic Shaping Overhead Accounting for ATM
•The router supports ATM overhead accounting only for the shape and bandwidth commands.
•If you enable ATM overhead accounting on a child policy, then you must enable ATM overhead accounting on the parent policy.
•In a policy map, you must either enable ATM overhead accounting for all classes in the policy or disable overhead accounting for all classes in the policy. You cannot enable overhead accounting for some classes and disable overhead accounting for other classes in the same policy.
•The encapsulation type used within a policy map and between the parent policy map and the child policy map (in a hierarchical policy map structure) must be consistent.
•When you enter the show policy-map session command, the resulting classification byte counts and the queueing feature byte counts do not match. This is because the classification byte count does not consider overhead, whereas the queueing features do consider overhead.
•You must attach a policy map that is configured with ATM overhead accounting to only an Ethernet interface (or an IP session on an Ethernet interface).
Information About Traffic Shaping Overhead Accounting for ATM
Benefits of Traffic Shaping Overhead Accounting for ATM
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.
BRAS and Encapsulation Types
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" section.
Subscriber Line Encapsulation Types
The router supports the following subscriber line encapsulation types:
•snap-rbe
•mux-rbe
•snap-dot1q-rbe
•mux-dot1q-rbe
•snap-pppoa
•mux-pppoa
•snap-1483routed
•mux-1483routed
•snap-rbe-dot1q
•mux-rbe-dot1q
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.
ATM Overhead Calculation
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 encapsulation type used by the BRAS
•The CPCS trailer overhead
•The encapsulation type used between the DSLAM and the CPE
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)
See Table 1 for the offset sizes, in bytes, derived from this formula.
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
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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 |
ATM Overhead Accounting and Hierarchical Policies
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.
How to Configure Traffic Shaping Overhead Accounting for ATM
Configuring Traffic Shaping Overhead Accounting for ATM in a Hierarchical Policy
SUMMARY STEPS
1. enable
2. configure terminal
3. policy-map policy-map-name
4. class class-map-name
5. bandwidth {bandwidth-kbps | percent percentage | remaining percent percentage} account {{{qinq | dot1q} {aal5 | aal3} {subscriber-encapsulation}} | {user-defined offset [atm]}}
6. bandwidth remaining ratio ratio [account {qinq | dot1q} [aal5 | aal3] {subscriber-encapsulation | user-defined offset [atm]}]
7. shape [average | peak] mean-rate [burst-size] [excess-burst-size] account {{{qinq | dot1q} {aal5 | aal3} {subscriber-encapsulation}} | {user-defined offset [atm]}}
8. end
DETAILED STEPS
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Step 1 |
enable
Router> enable |
Enables privileged EXEC mode. •Enter your password if prompted. |
Step 2 |
configure terminal
Router# configure terminal |
Enters global configuration mode. |
Step 3 |
policy-map policy-map-name
Router(config)# policy-map Business |
Creates or modifies the child policy and enters policy-map configuration mode. •Enter the policy map name. This is the name of the child policy. |
Step 4 |
class class-map-name
Router(config-pmap)# class video |
Assigns the traffic class that you specify for the policy map and enters policy-map class configuration mode. •Enter the traffic class name. This is the name of the previously configured class map. |
Step 5 |
bandwidth {bandwidth-kbps | percent percentage | remaining percent percentage} account {{qinq | dot1q} {aal5 | aal3} {subscriber-encapsulation}} | {user-defined offset [atm]}}
Router(config-pmap-c)# bandwidth 8000 account dot1q aal5 snap-pppoa |
Enables Class-Based Weighted Fair Queueing (CBWFQ) on the basis of the keywords and arguments specified, such as the following: •bandwidth-kbps—Specifies or modifies the minimum bandwidth allocated for a class that belongs to a policy map. Valid values are from 8 to 2488320, which represents from 1 to 99 percent of the link bandwidth. •percent percentage—Specifies or modifies the minimum percentage of the link bandwidth allocated for a class that belongs to a policy map. Valid values are from 1 to 99. •remaining percent percentage—Specifies or modifies the minimum percentage of unused link bandwidth allocated for a class that belongs to a policy map. Valid values are from 1 to 99. •account—Enables ATM overhead accounting. •qinq—Specifies queue-in-queue encapsulation as the BRAS-DSLAM encapsulation type. •dot1q—Specifies IEEE 802.1Q VLAN encapsulation as the BRAS-DSLAM encapsulation type. •aal5—Specifies the ATM adaptation layer 5 that supports connection-oriented variable bit rate (VBR) services. •aal3—Specifies the ATM adaptation layer 5 that supports both connectionless and connection-oriented links. •subscriber-encapsulation—Specifies the encapsulation type at the subscriber line. For more information, see the "Subscriber Line Encapsulation Types" section. •user-defined—Specifies the offset size that the router uses when calculating the ATM overhead. •offset—Specifies the offset size when calculating ATM overhead. Valid values are from -63 to +63 bytes. •atm—(Optional) Applies the ATM cell tax in the ATM overhead calculation. |
Step 6 |
bandwidth remaining ratio ratio [account {qinq | dot1q} [aal5 | aal3] {subscriber-encapsulation | user-defined offset [atm]}]
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: •ratio—Specifies the bandwidth-remaining ratio for the subinterface. Valid values are 1 to 100. The default value is 1. Note For the Cisco 7600 series router, valid values are from 1 to 10000. The default value is 1. •account—Enables ATM overhead accounting. •qinq—Specifies queue-in-queue encapsulation as the BRAS-DSLAM encapsulation type. •dot1q—Specifies IEEE 802.1Q VLAN encapsulation as the BRAS-DSLAM encapsulation type. •aal5—Specifies the ATM adaptation layer 5 that supports connection-oriented VBR services. •aal3—Specifies the ATM adaptation layer 5 that supports both connectionless and connection-oriented links. •subscriber-encapsulation—Specifies the encapsulation type at the subscriber line. For more information, see the "Subscriber Line Encapsulation Types" section. •user-defined—Specifies the offset size that the router uses when calculating the ATM overhead. •offset—Specifies the offset size, in bytes, when calculating ATM overhead. Valid values are from -63 to +63. •atm—(Optional) Applies the ATM cell tax in the ATM overhead calculation. |
Step 7 |
shape [average | peak] mean-rate [burst-size] [excess-burst-size] account {{{qinq | dot1q} {aal5 | aal3} {subscriber-encapsulation}} | {user-defined offset [atm]}}
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: •average—(Optional) The committed burst (Bc) that specifies the maximum number of bits sent out in each interval. •peak—(Optional) Specifies the maximum number of bits sent out in each interval (the Bc + excess burst [Be]). The Cisco 10000 router and the SIP400 (on the Cisco 7600 series router) do not support this option. •mean-rate—Also called committed information rate (CIR). Indicates the bit rate used to shape the traffic, in bits per second. •burst-size—(Optional) The number of bits in a measurement interval (Bc). •excess-burst-size—(Optional) The acceptable number of bits permitted to go over the Be. •account—Enables ATM overhead accounting. •qinq—Specifies queue-in-queue encapsulation as the BRAS-DSLAM encapsulation type. •dot1q—Specifies IEEE 802.1Q VLAN encapsulation as the BRAS-DSLAM encapsulation type. •aal5—The ATM adaptation layer 5 that supports connection-oriented variable bit rate (VBR) services. •aal3—Specifies the ATM Adaptation Layer 5 that supports both connectionless and connection-oriented links. You must specify either aal3 or aal5. •subscriber-encapsulation—Specifies the encapsulation type at the subscriber line. For more information, see the "Subscriber Line Encapsulation Types" section. •user-defined—Specifies the offset size that the router uses when calculating the ATM overhead. •offset—Specifies the offset size when calculating ATM overhead. Valid values are from -63 to +63 bytes. •atm—(Optional) Applies ATM cell tax in the ATM overhead calculation. Configuring both the offset and the atm options adjusts the packet size to the offset size and then adds ATM cell tax. |
Step 8 |
end
Router(config-pmap-c)# end |
Exits policy-map class configuration mode and returns to privileged EXEC mode. |
Verifying the Configuration of Traffic Shaping Overhead Accounting for ATM
SUMMARY STEPS
1. enable
2. show policy-map [policy-map-name]
3. show policy-map session
4. show running-config
5. exit
DETAILED STEPS
|
|
|
Step 1 |
enable
Router> enable |
Enables privileged EXEC mode. •Enter your password if prompted. |
Step 2 |
show policy-map [policy-map-name]
Router# show policy-map unit-test |
(Optional) Displays the configuration of all classes for a specified policy map or of all classes for all existing policy maps. •(Optional) Enter the policy map name. |
Step 3 |
show policy-map session
Router# show policy-map session |
(Optional) Displays the QoS policy map in effect for an IPoE/PPPoE session. |
Step 4 |
show running-config
Router# show running-config |
(Optional) Displays the contents of the currently running configuration file. |
Step 5 |
exit
Router# exit |
Exits privileged EXEC mode. |
Configuration Examples for Traffic Shaping Overhead Accounting for ATM
Example: Enabling Traffic Shaping Overhead Accounting for ATM
The following example shows how to enable ATM overhead accounting using a hierarchical policy map structure. The Child policy map has two classes: Business and Non-Business. The Business class has priority and is policed at 128,000 kbps. The Non-Business class has ATM overhead accounting enabled and has a bandwidth of 20 percent of the available bandwidth. The Parent policy map shapes the aggregate traffic to 256,000 kbps and enables ATM overhead accounting.
Notice that Layer 2 overhead accounting is not explicitly configured for the Business traffic class. If the class-default class of a parent policy has ATM overhead accounting enabled, you are not required to enable ATM overhead accounting on a child traffic class that does not contain the bandwidth or shape command. Therefore, in this example, the Business priority queue implicitly has ATM overhead accounting enabled because its parent class-default class has overhead accounting enabled.
bandwidth percent 20 account dot1q aal5 snap-dot1q-rbe
bandwidth percent 10 account dot1q aal5 snap-dot1q-rbe
shape 256000 account dot1q aal5 snap-dot1q-rbe
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
bandwidth remaining percent 80 account dot1q aal5 snap-dot1q-rbe
bandwidth remaining percent 20 account dot1q aal5 snap-dot1q-rbe
policy-map subscriber_line
bandwidth remaining ratio 10 account dot1q aal5 snap-dot1q-rbe
shape average 512000 account aal5 dot1q snap-dot1q-rbe
service-policy subscriber_classes
Example: Verifying Traffic Shaping Overhead Accounting for ATM
The following output from the show policy-map interface command indicates that ATM overhead accounting is enabled for shaping and disabled for bandwidth:
Router# show policy-map interface
Service-policy output:unit-test
Class-map: class-default (match-any)
30 second offered rate 800 bps, drop rate 0 bps
shape (average) cir 154400, bc 7720, be 7720
overhead accounting: enabled
overhead accounting: disabled
(queue depth/total drops/no-buffer drops) 0/0/0
(packets output/bytes output) 100/1000
The following output from the show policy-map session command indicates that ATM overhead accounting is enabled for shaping.
Router# show policy-map session output
SSS session identifier 2 -
Service-policy output: ATM_OH_POLICY
Class-map: class-default (match-any)
30 second offered rate 0 bps, drop rate 0 bps
(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 partial 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
shape average percent 10 account dot1q aal5 snap-rbe
Additional References
Related Documents
Standards
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No new or modified standards are supported by this feature, and support for existing standards has not been modified by this feature. |
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MIBs
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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 XE software releases, and feature sets, use Cisco MIB Locator found at the following URL: http://www.cisco.com/go/mibs |
RFCs
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No new or modified RFCs are supported by this feature, and support for existing RFCs has not been modified by this feature. |
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Technical Assistance
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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. |
http://www.cisco.com/cisco/web/support/index.html |
Feature Information for MQC Traffic Shaping Overhead Accounting for ATM
Table 2 lists the release history for this feature.
Use Cisco Feature Navigator to find information about platform support and software image support. Cisco Feature Navigator enables you to determine which Cisco IOS XE software images support a specific software release, feature set, or platform. To access Cisco Feature Navigator, go to http://tools.cisco.com/ITDIT/CFN/jsp/index.jsp. An account on Cisco.com is not required.
Note Table 2 lists only the Cisco IOS XE software release that introduced support for a given feature in a given Cisco IOS XE software release train. Unless noted otherwise, subsequent releases of that Cisco IOS XE software release train also support that feature.
Table 2 Feature Information for MQC Traffic Shaping Overhead Accounting for ATM
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MQC Traffic Shaping Overhead Accounting for ATM |
Cisco IOS XE Release 2.4 |
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. 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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