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When there are multiple VNS areas (or domains), the VNS's are connected by a Frame Relay PVC. This Frame Relay connection uses the Cisco Proprietary Network to Network Interface (SPNNI) protocol and is added when the Local Adjacency Information menu is completed. This Frame Relay PVC uses the default Frame Relay class 0. When necessary, you can modify Frame Relay class 0 with the cnffrcls command. Modifying Frame Relay class templates is described in the Cisco WAN Switching Command Reference in the Chapter, Frame Relay Connections.
This SPNNI connection will use trunk bandwidth between the nodes to which the VNS's are attached. In some VNS WAN switching networks, you may have to modify the default SPNNI connection parameters for your requirements. First you must be able to calculate the amount of bandwidth required for this SPNNI connection. The traffic over the SPNNI connection varies with the number of calls the VNS has to process.
To calculate the typical amount of bandwidth required for a SPNNI connection, you can use the following guidelines:
Using these guidelines and the expected number of calls per hour, you can calculate the SPNNI Frame Relay bandwidth. For example, say your network expects to handle 50000 VNS calls per hour and each call requires 5 messages to build and tear down the call.
The Frame Relay bandwidth for this example could be calculated as follows:
5 * (45 + 50) * 50000 / 3600 = 6597 = 51.5 kbps
no. max no. sec. octets Frame Relay
of msg of per per Bandwidth
msgs size calls hour second
per on the
call SPNNI
per hour
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