Inverse Multiplexing Atm; Virtual Trunking - Cisco BPX-BXM-155-8DX Installation And Configuration Manual

Chapter 1 The BPX Switch: Functional Overview
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Inverse Multiplexing ATM

Where greater bandwidths are not needed, the Inverse Multiplexing ATM (IMA) feature provides a low
cost trunk between two BPX switches.
The IMA feature allows BPX switches to be connected to one another over any of the 8 T1 or E1 trunks
provided by an IMATM module on an MGX 8220 shelf. A BNI or BXM port on each BPX switch is
directly connected to an IMATM module in an MGX 8220 by a T3 or E3 trunk. The IMATM modules
are then linked together by any of the 8 T1 or E1 trunks.
Refer to the Cisco MGX 8220 Reference and the Cisco WAN Switching Command Reference
publications for further information.

Virtual Trunking

Virtual trunking provides the ability to define multiple trunks within a single physical trunk port
interface. Virtual trunking benefits include the following:
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A virtual trunk may be defined as a "trunk over a public ATM service." The trunk really doesn't exist
as a physical line in the network. Rather, an additional level of reference, called a virtual trunk
number, is used to differentiate the virtual trunks found within a physical trunk port.
Figure 1-8 shows four Cisco WAN switching networks, each connected to a Public ATM Network via
a physical line. The Public ATM Network is shown linking all four of these subnetworks to every other
one with a full meshed network of virtual trunks. In this example, each physical line is configured with
three virtual trunks.
Release 9.3.0, Part Number 78-10674-01 Rev. D0, July 2001
Local and Remote Loopbacks
Connection local and remote loopbacks are managed at the user interface of the FRP endpoint
routing node or interface shelf. Remote loopbacks are not supported for DAX connections. The
command addlocrmtlp supports remote loopbacks at FRP DAX endpoints.
Testcon and Testdly
Tstcon is supported at the FRP endpoints in a non-integrated fashion and is limited to a pass/fail
loopback test. Fault isolation is not performed. This is the same limitation imposed on inter-domain
connections. Intermediate endpoints at the AIT and BNI cards do not support the tstcon feature.
Tstdelay is also supported for the FRP and ASI in a non-integrated fashion similar to that of the
tstcon command.
Reduced cost by configuring the virtual trunks supplied by the public carrier for as much bandwidth
as needed instead of at full T3, E3, or OC-3 bandwidths.
Utilization of the full mesh capability of the public carrier to reduce the number of leased lines
needed between nodes in the Cisco WAN switching networks.
Choice of keeping existing leased lines between nodes, but using virtual trunks for backup.
Ability to connect BNI or BXM trunk interfaces to a public network using standard ATM UNI cell
format.
Virtual trunking can be provisioned via either a Public ATM Cloud or a Cisco WAN switching ATM
cloud.
Cisco BPX 8600 Series Installation and Configuration
BPX Switch Operation
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