ATM Connections 7-35
Traffic Policing Examples
ABR Connection Policing
Available Bit Rate (ABR) connections are policed the same as the VBR connections, but in addition
use either the ABR Standard with VSVD congestion flow control method or the ForeSight option to
take advantage of unused bandwidth when it is available.
UBR Connection Policing
The contract for a unspecified bit rate connection is similar to the ABR connection service for bursty
data. However, UBR traffic is delivered only when there is spare bandwidth in the network.
When a connection is added, a VPI.VCI address is assigned, and UPC parameters are configured for
the connection. For each cell in an ATM stream, the VPI.VCI addresses are verified and each cell is
checked for compliance with the UPC parameters as shown in Figure 7-21.
Leaky Bucket 1
Leaky bucket 1 polices the UBR connection for PCR compliance. When CLP=No (UBR.1), all cells
that are compliant with leaky bucket 1 are applied to the network. However, these cells are treated
with low priority in the network with % utilization default of 1%.
Leaky Bucket 2
When CLP=Yes (UBR.2), CLP(0) cells that are compliant with leaky bucket 1 are sent to leaky
bucket 2. Since SCR=0 for leaky bucket 2, the bucket is essentially always full, and all the CLP(0)
cells sent to leaky bucket 2 are therefore tagged with CLP being set to 1. This allows the network to
recognize these UBR cells as lower priority cells and available for discard in the event of network
congestion.
