Filter
Top Products
PNNI in an ATM Network
893-01006-C
4-19
Logical Links
A link between two nodes is a logical link. A logical link may be a physical link or
a virtual path or channel. PNNI supports signaling and routing over multiple
virtual path connections (VPCs) to multiple destinations through a single physical
interface. In this situation, each VPC configured for use as a logical link has a
signaling channel associated with it. Virtual channels within these VPCs are
controlled only by the associated signaling channel of that particular VPC.
The default signaling channel (VPI=0) on the same physical interface does not
control virtual channels within other VPCs used as logical links, but it does
control all the remaining virtual channels and virtual paths on the physical link.
Thus, on Centillion 50/100 and Model 5000BH switches, users can configure up
to three logical links or VPCs on a given physical interface. This feature is helpful
when users want to interconnect geographically separated locations through a
WAN, as shown in Figure 4-7
.
Caution:
You cannot configure an ELAN (LECs and LES/BUS) that spans
multiple logical links on the same physical interface. For example, in
Figure 4-7
, you cannot have LEC (switch B) and LEC (switch C) on the same
ELAN because the switch is unable to set up a point-to-multipoint (PMP) SVC
that branches on more than one VPI on the same port. If LECs on the two
remote switches attempt to join the same ELAN, then only the first one will be
successful because it is not possible to set up the relevant add party requests
for the second LEC.