Specifications

1-10
Cisco MGX 8800/8900 Series Software Configuration Guide
Release 5.1, Part Number OL-6482-01, Rev. A0, January 25, 2005
Chapter 1 Preparing for Configuration
Typical Topologies
Figure 1-3 Virtual Trunk Topology
A virtual trunk provides a private virtual network path through an independent network such as a public
ATM network. Using virtual trunks, Company A can establish a private virtual path between two sites
using a public ATM network that supports this feature.
From Company A’s point of view, it has a private virtual path between the two sites that can support
multiple virtual circuits (VCs). Company A’s network topology is completely private, as all
communications are simply passed between edge devices, with no need for translation or routing.
To accomplish this configuration, the virtual trunk supports the Service Specific Connection Oriented
Protocol (SSCOP) (virtual channel identifier [VCI = 5]), Private Network-to-Network Interface (PNNI)
(VCI = 18) and Integrated Local Management Interface (ILMI) (VCI = 16) signaling protocols.
Figure 1-3 shows two virtual trunks, Virtual Trunk A and Virtual Trunk B. At Private Switch A, both
virtual trunks use the same line to connect to the core ATM network. Within the core ATM network, soft
virtual permanent paths (SPVPs) are defined to enable direct communications between the core edge
nodes. The result is that Private Switch A has virtual trunks to Private Switches B and C and
communicates with them as though they were directly connected.
A
B
Core ATM
network
SPVP
Edge
switch 1
Legend
Physical line
Private
switch A
Edge
switch 2
Edge
switch 3
Private
switch B
A
Private
switch C
B
Virtual trunk
46508 SPVP