Setup guide

C-1
Cisco 6400 Software Setup Guide
OL-1183-04
A P P E N D I X C
Optimizing the Number of Virtual Connections on
the Cisco 6400
This appendix describes how to optimize the number of supported virtual connections on the Cisco 6400
carrier-class broadband aggregator by:
• Properly assigning virtual path identifier (VPI) and virtual channel identifier (VCI) values
• Reducing Input Translation Table (ITT) memory fragmentation
For general information on configuring virtual connections, see the “Configuring Virtual Connections”
chapter of the ATM Switch Router Software Configuration Guide.
Note The method of assigning VPIs and VCIs can affect how you configure virtual connections on network
devices that are connected to the Cisco 6400.
This appendix includes the following sections:
• An Overview of the ITT and Virtual Connection Limitations, page C-1
• Guidelines for Maximizing the Number of Virtual Connections, page C-3
An Overview of the ITT and Virtual Connection Limitations
The Cisco 6400 supports a maximum of 32K virtual connections, a limit determined by a hardware data
structure in the node switch processor (NSP) called the ITT. The ITT consists of two banks (Bank 0 and
Bank 1), each of which can hold a maximum of 32K entries. Each configured virtual connection occupies
two ITT entries (one for each direction of cell flow). Unidirectional connections (such as
point-to-multipoint connections) occupy only one ITT entry.
ITT entries are not maintained for:
• Permanent virtual circuit (PVC) legs that are not connected
• Connection legs on ATM 0/0/0
• PVCs with one or both interfaces in the down state
• Any connection that does not receive cells (such as point-to-multipoint leaves)