A network constructed properly along the lines of Figure 13.1 could serve
a continent.
It is equally true that as so far developed, a network that offers almost exclusively
E-Line EVCs would better be implemented with MPLS or another circuit technology,
rather than with bridges. A VLAN is optimized for providing a multipoint-to-multipoint
service. If it has only two endpoints, it certainly works, but many of the bridge protocols
and much of data plane hardware is then wasted. However, techniques for efficiently
supporting point-to-point circuits with bridges are in development and are being offered
for standardization.
Finally, when assessing whether or not a large number of E-Line EVCs are needed, it
is important to understand that connecting thousands of subscribers to their ISP does
not require thousands of E-Line EVCs. As described in ???Number of VLANS,??? one pair
of VLANs is sufficient to create an EVC with a few privileged points (the ISP??™s routers)
and thousands of unprivileged points (the subscriber??™s routers). It can prevent the subscribers
from communicating directly with each other, allow them to communicate with
414 Chapter 13
the routers, allow the routers to communicate with each other, and efficiently distribute
multicasts from the router, using only one EVC comprising two VLANs.
Pages:
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933