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4-20 SmartCell 6A000 User Guide
Traffic Mana
g
ement Switch Administration
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.
SmartCell ZX# add pvc
ConnType(PTP) :
LowPort(A1) : b1
LowVPI(0) :
LowVCI(33) :
HighPort(A1) : b2
HighVPI(0) :
HighVCI(34) :
FwdTrafficDescriptorIndex(1) : 3
< forward traffic descriptor index
BkwTrafficDescriptorIndex(1) : 2
< backward traffic descriptor index
SmartCell ZX#
Notice in the example above that you can use different traffic descriptors for forward and backward traffic.
4.6.2 Call Admission Control Policy
Call admission control (CAC) defines the bandwidth allocation scheme (on a per-port basis) used by the SmartCell
6A000 when setting up connections. The SmartCell 6A000 offers three schemes.
• Conservative
• Moderate
• Liberal
As mentioned above, when a call is being set up, the source signals to request a certain amount of bandwidth. The CAC
policy determines the amount of risk the SmartCell 6A000 is willing to take regarding the available bandwidth when
establishing the call on a port.
For instance, if the CAC policy for a port is "conservative," the SmartCell 6A000 allows calls to be established through
this port only if available bandwidth on the port either meets or exceeds the amount requested by the source. If there
is not enough bandwidth, the port rejects the connection. The "liberal" CAC policy allows calls to be set up even if
bandwidth is insufficient to meet the source's request.The liberal CAC policy resembles a telephone company's
resource allocation scheme. The telephone system works as long as everyone doesn't try to make a call at the same
time. Liberal CAC policy assumes enough bandwidth is available to service all calls provided the majority of
connections don't transmit at the same time. Using the liberal CAC policy results in some dropped and retransmitted
cells. However, it's usually adequate for the stochastic traffic that exists on most LANs. Moderate CAC policy is a
balance between conservative and liberal port bandwidth allocation— taking risks that are tempered by an evaluation
of the traffic types that constitute the connections on the port.