Specifications

1-5
Cisco MGX 8850 (PXM45) and MGX 8950 Software Configuration Guide
Release 3, Part Number 78-14788-01 Rev. C0, January 2004
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, they have 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, 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.
DSL Aggregation
In the DSL edge aggregation topology, the switch is colocated with Digital Subscriber Line Access
Multiplexers (DSLAMs) and communicates with one or more core switches at remote locations. The
switch aggregates the DSL traffic from multiple DSLAMs and packages it for high-speed
communications over the core.
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