Feature History For Overhead Accounting; Atm Overhead Accounting - Cisco 10000 Series Configuration Manual
Quality of service configuration guide
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Overhead Accounting Features
Feature History for Overhead Accounting
Cisco IOS Release
Release 12.3(7)XI7
Release 12.2(28)SB
Release 12.2(31)SB2
Release 12.2(33)SB
Release 12.2(33)SB2
1. Performance Routing Engine (PRE)
ATM Overhead Accounting
ATM overhead accounting enables the router to account for various encapsulation types when applying
QoS to packets. Typically, in Ethernet Digital Subscriber Line (DSL) environments, the encapsulation
from the router to the DSLAM is Gigabit Ethernet and the encapsulation from DSLAM to customer
premise 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 accounting
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.
The router uses the encapsulation type you configure to calculate the ATM overhead per packet. When
calculating ATM overhead at the subscriber line, the router considers the encapsulation used between
the router and DSLAM and between the DSLAM and CPE (as described in the following list). You
configure the encapsulation type and the router calculates the overhead associated with ATM cell
segmentation.
•
•
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
Cisco 10000 Series Router Quality of Service Configuration Guide
10-2
Description
The ATM Overhead Accounting feature was introduced on
the router to enable the router to account for various
encapsulation types when applying QoS to packets.
The ATM Overhead Accounting feature was introduced in
Cisco IOS Release 12.2(28)SB.
The Traffic Shaping Overhead Accounting for ATM
feature was introduced on the PRE3.
The Ethernet Overhead Accounting feature was introduced
on the PRE2, PRE3, and PRE4. ATM overhead accounting
was enhanced on the PRE3 to allow a user-defined number
of overhead bytes and introduced on the PRE4. The PRE4
inherits all overhead accounting features from the PRE3.
The MLP on LNS with HQoS and ATM Overhead
Accounting feature was introduced on the PRE3 and
PRE4.
IEEE 802.1Q and qinq encapsulation are typically used between the router and DSLAM. Because
the DSLAM removes the encapsulation, the router does not account for this encapsulation in the
calculation.
The encapsulation used between the DSLAM and the CPE is based on the Subnetwork Access
Protocol (SNAP) and multiplexer (MUX) formats of ATM Adaptation Layer 5 (AAL5) and AAL3.
These encapsulation types can be routed bridge encapsulation (RBE), PPP over Ethernet (PPPoE),
or PPP over ATM (PPPoA), and IP. Because the DSLAM treats IP and PPPoE packets as payload,
the router does not account for IP and PPPoE encapsulation in the calculation.
"Overhead Calculation on the Router" section on page
Chapter 10
Overhead Accounting
Required PRE
PRE2
PRE2
PRE3
PRE2
PRE3
PRE4
PRE3
PRE4
10-5.
1
OL-7433-09
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