Information Technology Reference
In-Depth Information
Figure22-6 Variable Bit-rate Traffic Shaping
MBS
PCR
SCR
Time
VBR traffic shaping is an effective approach for a bursty network. Parameters used are peak cell rate
(PCR), sustainable cell rate (SCR), and maximum burst size (MBS). When a traffic contract has been
agreed upon, the ATM network guarantees the transmission of cells within the VBR parameters. The
number of cells allowed to exceed SCR is set by MBS and bound by the PCR.
The three traffic contract parameters are defined below:
•
PCR
—Maximum rate at which the source can send cells.
•
SCR
—Bound on the long-term average cell rate.
•
MBS
—Maximum number of cells that can be sent above SCR at PCR.
Creating a Mapping Between a Destination Address and PVC
A common source of problems is the incorrect configuration of the ATM mapping. Basically, after
configuring the PVC itself, you must instruct the router on which PVC needs to be used to reach a
specific destination. You have three ways to ensure the right mapping:
•
If you put the PVC on a point-to-point subinterface, the router will assume that there is only one
point-to-point PVC configured on the subinterface. Therefore, any IP packet with a destination IP
address in the same subnet will be forwarded on this VC. This is the simplest way to configure the
mapping and is therefore the recommended version.
•
If you put the PVC in a point-to-multipoint subinterface or the main interface, you will have to
create a static mapping. Refer to the “Command Mode” section for a configuration example.
•
You can use Inverse ARP to create the mapping automatically. Refer to the documentation for
configuration guidelines.
Troubleshooting Connectivity Issues
The user can often have the feeling that part of the information is being lost between the two routers.
The most common symptoms are these:
