Virtual Trunk Interfaces; Virtual Trunk Traffic Classes; Virtual Trunk Transmit Queuing - Cisco BPX 8620 Installation And Configuration Manual

Connection Management
Within the ATM cloud one virtual trunk is equivalent to one VPC. Since the VPC is switched with just
the VPI value, 16 VCI bits (from the ATM cell format) of the ATM cell header are passed transparently
through to the other end.
If the public ATM cloud consists of BPX nodes using BXM cards, the access points within the cloud are
BXM ports. If the cloud consists of IGX nodes, the access points within the cloud are UXM ports.

Virtual Trunk Interfaces

The two ends of a virtual trunk can have different types of port interfaces. For example, a virtual trunk
contains a T3 port at one end of the ATM cloud and an OC-3 port at the other end.
However, both ends of the trunk must have the same bandwidth, connection channels, cell format, and
traffic classes. This requirement is automatically checked during the addition of the trunk.

Virtual Trunk Traffic Classes

All types of traffic from a private network using Cisco nodes are supported through a public ATM cloud.
The CBR, VBR, and ABR configured virtual trunks within the cloud should be configured to carry the
following correct types of traffic.
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A CBR configured trunk is best suited to carry delay sensitive traffic such as voice/data, streaming video,
and ATM CBR traffic, and so on.
A VBR configured trunk is best suited to carry frame relay and VBR traffic, and so on.
An ABR configured trunk is best suited to carry ForeSight and ABR traffic, and so on.
Two-stage queueing at the egress of BXM virtual trunks to the ATM cloud allows shaping of traffic
before it enters the cloud. However, the traffic is still routed on a single VPC in the cloud and may be
affected by the traffic class of the VPC selected.
You can configure any number of virtual trunks up to the maximum number of virtual trunks per slot
(card) and the maximum number of logical trunks per node. These trunks can be any of the three trunk
types: CBR, VBR, or ABR.
You can configure any number of virtual trunks between two ports up to the maximum number of virtual
trunks per slot and the maximum number of logical trunks per node. These trunks can be any of the three
trunk types.

Virtual Trunk Transmit Queuing

In the BXM, the egress cell traffic out of a port is queued in the following two stages:
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Cisco BPX 8600 Series Installation and Configuration
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CBR Trunk: ATM CBR traffic, voice/data/video streaming, and so on.
VBR Trunk: ATM VBR traffic, frame relay traffic, and so on.
ABR Trunk: ATM ABR traffic, ForeSight traffic, and so on.
First they are queued per Virtual Interface (VI), each of which supports a virtual trunk.
Within each VI, the traffic is queued as per its normal OptiClass traffic type.
Chapter 24 Configuring BXM Virtual Trunks
Release 9.3.30, Part Number 78-12907-01 Rev. E0, May 2005