Cabletron Systems 04-0053-01 Manual De Usuario

SmartSwitch ATM User Guide   4-7

Routing

Route Metrics  

Remember that while some special network configurations may require the 

 to be zero (0), setting 

 to less than three seconds 

may cause a UNI route to fail unnecessarily. For this reason, care should be 
taken when setting the 

 to less than three seconds.

4.4

ROUTE METRICS

Route metrics are assigned to routes using a metric tag (one of the input parameters for 

). The metric tag 

specifies a particular pair of incoming and outgoing metrics contained within a list of metrics. Metrics are created using 
the 

 command (whether PNNI, IISP, or UNI routes). Each metric pair specifies a set of values that 

describe a route’s Service Category, cell rates, bandwidth, and administrative weight. Locally, metric values determine 
the behavior of the link. Within PNNI networks, PNNI’s Generic Call Admission Control (GCAC) assesses metrics 
when establishing calls.

4.4.1

Administrative Weights

The administrative weight (

parameter) of a metric allows you to control the use of a route for call set ups. By 

default, a metric assigns the lowest value (5040) to the 

 parameter. Values less than 5040 (for example 500) 

are considered to have greater administrative weight. Among parallel routes, the route with the greatest administrative 
weight is seen as the preferred route; subsequently, most calls are set up through that route. Other parallel routes with 
lower administrative weights are used as “backup” routes These backup routes will be used only if the route with the 
greatest administrative weight is either out of bandwidth or down.

4.4.2

Creating Route Metrics

The following section describes how to create a route metric and assign it to a route.

For a complete description of all 

 parameters, see the SmartSwitch 

ATM Switch Reference Manual.

In the following example, a metric pair is created (with metric tag of 9), which specifies CBR as the Service Category, 
administrative weight of 200, Max Cell Rate of 1000 cells per second, and an Available Cell Rate of 750 cells per 
second.

The default value 

 that appears in the 

 command means 

“If no value is specified for the parameter, the parameter is not used within the 
metric.” It does NOT mean that the parameter does not accept values.