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Tag Switching 9-9
Tag Switching and the BPX 8650
Virtual Switch Interfaces
Figure 9-5 shows how virtual switch interfaces are implemented by the BPX switch in order to
facilitate tag switching. A virtual switch interface (VSI) provides a standard interface so that a
resource in the BPX switch can be controlled by additional controllers other than the BPX controller
card such as a tag switch controller.
The tag switch controller is connected to the BPX switch using ATM T3/E3/OC3 interfaces on the
TSC device (a 7200 or 7500 series router) and on a BXM card. The ATM OC3 interface on the 7200
router is provided by an ATM port adapter, on the 7500 router by an AIP or a VIP with ATM Port
Adapter, and for the BXM front card by an ATM OC3 4-port or 8-port back card.
Figure 9-5 BPX Switch VSI Interfaces
A distributed slave model is used for implementing VSI in a BPX switch. Each BXM in a BPX
switch is a VSI slave and communicates with the controller and other slaves, if needed when
processing VSI commands. The VSI master sends a VSI message to one slave. Depending on the
command, the slave either handles the command entirely by itself, or communicates with a remote
slave to complete the command. For example, a command to obtain configuration information would
be processed by one slave only. A command for connection setup would cause the local slave to
communicate with the remote slave in order to coordinate with both endpoints of the connection.
Figure 9-6 shows a simplified example of a connection setup with endpoints on the same slave
(BXM VSI), and an example of a connection setup with endpoints on different slaves (BXM VSIs)
is shown in Figure 9-7.
S6878
Tag
switch
controller
VSI master
BXM 3
BXM 1
VSI slave
BXM 2
VSI slave
Router
(7200 or 7500)
VPI.VCI A (VSI master to slave I/F)
VPI.VCI B (VSI master to slave I/F)
VPI.VCI C (VSI master to slave I/F)
To ATM edge router or other ATM LSR (BPX 8650 or LS 1010)
Note:
Dotted lines indicate
VSI to VSI slave I/Fs
ATM OC3 interface
Backplane
VSI slave
BPX switch
BPX 8650 Label Switch Router (LSR)