Cisco BPX 8650, Руководство по установке и настройке

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24-2
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
Overview
The ATM equipment in the cloud must support Virtual Path switching and moving incoming cells based on
the VPI in the cell header. Within the cloud, one virtual trunk is equivalent to one VPC. Because the VPC is
switched with just the VPI value, the 16 VCI bits (from the ATM cell format) of the ATM cell header are
passed transparently through to the other end. The VCI bits within the header are passed transparently through
the entire cloud (see Figure 24-1).
The BXM card physical trunk interface to the ATM cloud is a standard ATM UNI or NNI interface at the
cloud access point. The administrator of the ATM cloud, for example, Service Provider specifies whether
the interface is UNI or NNI, and also provides the VPI to be used by a virtual trunk across the cloud.
The following are the two general types of virtual trunks:
•
Automatic Routing Management Virtual Trunks—Specifies the PVP or SPVP connections that carry
Automatic Routing Management PVC connections.
•
VSI Virtual Trunks—Carries the MPLS or PNNI connections for the PVP or SPVP connections.
Typical ATM Hybrid Network with Virtual Trunks
With the BPX switch, you can set up virtual networks with either the Broadband Network Interface
(BNI) card or with the BXM card. Virtual trunks can originate and terminate on:
•
BXMs to BXMs;
or
•
BXMs to UXMs (IGX switch);
or
•
BNIs to BNIs
• But not
BNIs to BXMs or UXMs.
When the Cisco virtual trunk interface is a BXM interface accessing a port in the Public ATM network,
the Public ATM port may be a UNI or NNI port on a BXM, ASI, or other standards-compliant UNI or
NNI port.
When the Cisco virtual trunk interface is a BNI interface accessing a port in the Public ATM network,
the Public ATM port must be a port on a BPX.
Figure 24-1 shows three Cisco WAN switching networks, each connected to a Public ATM Network
through a physical interface. The Public ATM Network is shown linking all three of these subnetworks
to every other one with a full meshed network of virtual trunks. In this example, each physical interface
is configured with two virtual trunks.