3Com CoreBuilder 7000 Operation Manual page 103

VP Tunneling 103
have the same source and destination are assigned the same VPI value,
they are switched more efficiently by the VP switch.
LANE over WAN
The WAN VP switch allocates the VPI values which are then used to
establish the CoreBuilder VP tunnels. A CoreBuilder 7000HD VP tunnel is
established with the appropriate VPI and connected to a port of the WAN
VP switch. This ATM connection is established manually (permanent
virtual path). A similar connection is established at the other side of the
WAN to the other CoreBuilder 7000HD. Once these connections are in
place, the signaling and ILMI channels of the VP tunnel between the two
CoreBuilders operate to set up a NNI connection between them; this
connection is transparent to the WAN VP switch.
Using this method, an emulated LAN can be set up over an ATM WAN VP
switch.
Multicast Channels
When setting up an emulated LAN over a WAN VP switch, you need to
allocate one channel needs for multicast transmissions to handle the
multicast messages of the LES/BUS server. Providing that the WAN VP
switch has a multicast capability, the WAN VP switch allocates the
appropriate VPI values for the multicast channel, one for each side of the
WAN.
In setting up such a system, assign the largest Net Prefix among all
participating CoreBuilder switches to the multicast server switch (for
example, the CoreBuilder 7000 which contains the LES/BUS). This causes
the multicast server to assume a network profile, ensuring that it will
determine the VPI/VCI values for the connection.
VP Tunneling LAN Topology
The topology connecting the CoreBuilder 7000HD switch using tunnels is
a star topology. Figure 36 shows a LAN over WAN using VP tunneling.
The CoreBuilder 7000 switch C contains the active LES/BUS LANE
services. Broadcast messages are sent out from switch C over the
point-to-multipoint channel to the other two switches.