Introduction 1-15
Traffic and Congestion Management
When cells are received from the network for transmission out a port, egress queues at that port
provide additional buffering based on the service class of the connection.
OptiClass
OptiClass provides a simple but effective means of managing the quality of service defined for
various types of traffic. It permits network operators to segregate traffic to provide more control over
the way that network capacity is divided among users. This is especially important when there are
multiple user services on one network.
Rather than limiting the user to the four broad classes of service initially defined by the ATM
standards committees, OptiClass can provide up to 16 classes of service (service subclasses) that can
be further defined by the user and assigned to connections. Some of the COS parameters that may
be assigned include:
• Minimum bandwidth guarantee per subclass to assure that one type of traffic will not be
preempted by another.
• Maximum bandwidth ceiling to limit the percentage of the total network bandwidth that any one
class can utilize.
• Queue depths to limit the delay.
• Discard threshold per subclass.
These class of service parameters are based on the standards-based Quality of Service parameters
and are software programmable by the user. The BPX switch provides separate queues for each
traffic class.
AutoRoute
With AutoRoute, connections in Cisco WAN switching networks are added if there is sufficient
bandwidth across the network and are automatically routed when they are added. The user only
needs to enter the endpoints of the connection at one end of the connection and the IPX switch, IGX
switch, and BPX switch software automatically set up a route based on a sophisticated routing
algorithm. This feature is called AutoRoute. It is a standard feature on the IPX switch, IGX switch,
BPX switch, and MGX 8220.
System software automatically sets up the most direct route after considering the network topology
and status, the amount of spare bandwidth on each trunk, as well as any routing restrictions entered
by the user (e.g. avoid satellite links). This avoids having to manually enter a routing table at each
node in the network. AutoRoute simplifies adding connections, speeds rerouting around network
failures, and provides higher connection reliability.
Cost-Based AutoRoute
Cost-based route selection can be selectively enabled by the user as the route selection per node.
With this feature a trunk cost is assigned to each trunk (physical and virtual) in the network. The
routing algorithm then chooses the lowest cost route to the destination node. The lowest cost routes
are stored in a cache to reduce the computation time for on-demand routing.
Cost-based routing can be enabled or disabled at anytime, and there can be a mixture of cost-based
and hop-based nodes in a network.
The section, Cost-Based Connection Routing, contains more detailed information about cost-based
AutoRoute.
