Hierarchical Shaping And Oversubscription; Active Atm Vcs - Cisco 10000 Series Configuration Manual
Quality of service configuration guide
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Chapter 9
Shaping Traffic
The SAR uses weighted round-robin scheduling to schedule the PVP VCs onto the wire. The SAR also
does the following:
•
•
•
•
The priority of the PVP is the same as the priority of CBR VCs on an interface. If the physical interface
experiences congestion, the PVPs and any CBR VC have priority over VBR-nrt VCs and unspecified bit
rate (UBR) VCs.
Hierarchical Shaping and Oversubscription
You can oversubscribe the PVP bandwidth by configuring the VCs in such a way that the sum of the VCs'
bandwidths exceeds the configured rate of the PVP. The atm over-subscription-factor command is used
to configure oversubscription. This command sets up flow-control between the SAR and the VTMS, and
provides Caller Admission Control (CAC) based on the configured oversubscription value. Valid values
for oversubscription are from 0 (no oversubscription allowed) to 10.
You cannot oversubscribe the physical interface by oversubscribing the interface's PVPs. For a given
interface, the sum of the PVPs' bandwidth must be less than or equal to the physical interface speed,
minus the appropriate overhead. PVPs are subject to the same CAC mechanisms as the VCs.
The current oversubscription mechanism is optimized for VC-level fairness. When PVP congestion
occurs, the router cannot guarantee bandwidth allocation to an IP traffic class on a given VC.
The current oversubscription mechanism is optimized for VCs—it is not designed to handle PVP
congestion. If VCs are oversubscribed and PVP congestion occurs, VC shaping accuracy and bandwidth
distribution can degrade.
Active ATM VCs
Table 9-1
hierarchical shaping.
Table 9-1
Line Card
E3/DS3
OC-3
OC-12
OL-7433-09
Assigns high rate VCs a high weighting
Ensures that cells are scheduled in accordance with the configured rate of the PVP
Offers per-VC buffering to accommodate small bursts at the VC packet level
Ensures that transmitted cells conform to ATM transmission standards, including cell delay
variation tolerance (CDVT)
lists the maximum number of active VCs supported on ATM line cards when configured for
Active VCs on ATM Line Cards
Maximum VCs per Port
4,096
8,192
16,384
Maximum VCs per Module
32,768
32,768
16,384
Cisco 10000 Series Router Quality of Service Configuration Guide
Traffic Shaping
VBR, CBR, Shaped UBR VCs
28,672
28,672
16,384
9-7
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