Cabletron Systems 9A100 manual Call Admission Control Policy

Switch Administration TrafficManagement

A user-defined PVC must have user-defined traffic descriptors. For instance, if a video link over a PVC requires a constant data flow of 5000 kb/s and a peak cell rate of 8000 kb/s, create a traffic descriptor for CBR traffic that specifies 5000 as the sustained cell rate and 8000 as the peak cell rate.

SmartSwitch # add trafficdescriptor
TrafficType(UBR)	: cbr
TrafficDescriptorType(2)	: 3
PCRCLP01(100)	: 8000
PCRCLP0(100)	:
SCRCLP01(0)	: 5000
SCRCLP0(0)	:
MBSCLP01(0)	: 10000
MBSCLP0(0)	:
QOSCLASS(1)	:
AalType(5)	:
SmartSwitch #

Each traffic descriptor is identified by a unique index number. Use the index number to specify which traffic descriptor to use when setting up a PVC. For example, the add pvc command prompts you for the traffic descriptor index.

SmartSwitch # add pvc
ConnType(PTP)	:
LowPort( )	: b1
LowVPI( )	:0
LowVCI( )	:100
HighPort( )	: b2
HighVPI( )	:0
HighVCI( )	:100
FwdTrafficDescriptorIndex( )	: 3	< forward traffic descriptor index
BkwTrafficDescriptorIndex( )	: 2	< backward traffic descriptor index
SmartSwitch #

Notice in the example above that you can use different traffic descriptors for forward and backward traffic.

4.6.2Call Admission Control Policy

Call Admission Control (CAC) policy defines the bandwidth allocation scheme used by the CAC when setting up connections. The SmartSwitch 9A100 offers three schemes that can be set on a per-port, per-service class basis,

•Conservative

•Moderate

•Liberal

Under conservative policy, the CAC allocates bandwidth closest to the requested bandwidth and QoS parameters. Conversely, liberal policy causes the CAC to allocate the least amount of bandwidth. And the CAC under moderate policy allocates intermediate amounts of bandwidth.

Depending on the type of traffic on your network, each of these CAC policies has its advantages. For instance, liberal policy allows a larger number of connections over that of the conservative or moderate policy. Liberal policy assumes that the traffic pattern of individual VCs does not overlap most of the time. For example, if VC1 and VC2 are created under the liberal CAC policy, it’s assumed that the probability of both VCs sending large bursts of cells at the same time is relatively low. On the other hand, conservative policy assumes that there might be a larger overlap of traffic from different VCs, and provides each VC with bandwidth closer to the requested bandwidth. This higher bandwidth provides a guarantee of quality for each VC.

SmartSwitch 9A100 User Guide 4-19