Cisco BPX 8650, Installation And Configuration Manual

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24-9
Cisco BPX 8600 Series Installation and Configuration
Release 9.3.30, Part Number 78-12907-01 Rev. E0, May 2005
Chapter 24 Configuring BXM Virtual Trunks
Connection Management
Cell Transmit Address Translation
All cells transmitted to a virtual trunk have a translated cell address. This address consists of a VPI
chosen by the user and a VCI (ConId) chosen internally by the software. The trunk firmware is
configured by the software to perform this translation.
Cell Receive Address Lookup
The user-chosen VPI is the same for all cells on a virtual trunk.
At the receiving end, multiple virtual trunks can send cells to one port. The port must be able to
determine the correct channel for each of these cells.
The VPI is unique on each trunk for all the cells, but the VCI may be the same across the trunks. Each
port type has a different way of handling the incoming cell addresses. Only the BXM and UXM are
discussed here.
Selection of Connection Identifier
For connections, the associated connection are selected from a pool of connection for the entire card.
Each virtual trunk can use the full range of acceptable conid values. The range consists of all the 16-bit
values (1 to 65535) excluding the node numbers and blind addresses. A port uses the VPI to differentiate
connections that have the same conid.
You can change the number of channels per virtual trunk once the trunk has been added to the network.
Decreasing the number of channels on an added virtual trunk causes connection reroutes; whereas,
increasing the number of channels on an added virtual trunk will NOT cause connection reroutes.
Routing VPCs over Virtual Trunks
A VPC is not allowed to be routed over a virtual trunk. The routing algorithm excludes all virtual trunks
from the routing topology. The reason for this restriction is due to how the virtual trunk is defined within
the ATM cloud.
The cloud uses a VPC to represent the virtual trunk. Routing an external VPC across a virtual trunk
would consist of routing one VPC over another VPC. This use of VPCs is contrary to its standard
definition. A VPC should contain multiple VCCs, not another VPC. To avoid any nonstandard
configuration or use of the ATM cloud, VPCs cannot be routed over a virtual trunk through the ATM
cloud.
VPC Configuration with the ATM Cloud
In order for the virtual trunk to successfully move data through an ATM cloud, the cloud must provide
some form of connectivity between the trunk endpoints. The ATM equipment in the cloud must support
virtual path switching and move incoming cells based on the VPI in the cell header.
A virtual path connection (VPC) is configured in the cloud to join two endpoints. The VPC can support
either CBR, VBR, or ABR traffic. A unique VP ID per VPC is used to moved data from one endpoint to
the other. The BPX nodes at the edge of the cloud send in cells that match the VPCs VPI value. As a
result, the cells are switched from one end to the other of the ATM public cloud.