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Cisco MGX 8850 (PXM1E/PXM45), Cisco MGX 8950, Cisco MGX 8830, and Cisco MGX 8880 Configuration Guide
Release 5.0.10, OL-3845-01 Rev. B0, August 16, 2004
Chapter 1 Preparing for Configuration
Typical Topologies
The Cisco MGX 8850 (PXM1) node in Figure 1-2 is called a feeder node. In the multiservice edge
aggregation topology, the feeder node is co-located with other ATM equipment and communicates with
one or more core switches at remote locations. The switch aggregates the traffic from local ATM devices
and packages it for high-speed communications over the core. Cisco MGX 8850 (PXM1E/PXM45) and
Cisco MGX 8830 switches support feeder connections from Cisco MGX 8230, Cisco MGX 8250,
Cisco MGX 8850 (PXM1), and Cisco IGX nodes.
Typically, multiservice edge nodes communicate with colocated ATM devices over relatively slow
broadband trunks such as DS3 and E3 trunks. The multiservice edge node communicates with core nodes
using relatively fast links such as OC-12, OC-48, and STM-16 trunks.
Cisco MGX edge nodes also support virtual trunks as shown in Figure 1-3.
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
egend
Physical line
Private
switch A
Edge
switch 2
Edge
switch 3
Private
switch B
A
Private
switch C
B
Virtual trunk
46508
SPVP
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