User guide

Internetworking Primer A-19
LANs and WANs
Figure A-7 Multipoint WAN
Frame Relay
Frame Relay is a packet-switching data communications technology that can connect
multiple network devices on a multipoint WAN. The design of Frame Relay WANs can
have impact on aspects of higher layer protocols such as IP, IPX, and AppleTalk (for
example, the split-horizon aspect of routing protocols). Frame Relay is called a
nonbroadcast multiaccess technology, because there is no broadcast channel. Broadcasts
are transmitted by sending packets to all network destinations.
Two common topologies that can be used in a Frame Relay solution:
• Fully meshed topology
Every Frame Relay network device has a permanent virtual circuit (PVC) to every other
device on the multipoint WAN. Any update sent by one device will be seen by every
other. If this design is used, the entire Frame Relay WAN can be treated as one data link.
• Partially meshed topology
This is also often called a “star” or “hub-and-spoke” topology. In a partially meshed
topology, not every device on the Frame Relay cloud has a PVC to every other device.
In this topology, subinterfaces should be investigated and probably implemented to
solve design issues.
H3114
Router B
Router A
Router D
Router C
WAN