The Radio Aware Routing (RAR) feature is implemented using the MANET (Mobile adhoc network) infrastructure comprising of different
components such as PPPoE, Virtual multipoint interface (VMI), QoS, routing protocol interface and RAR protocols.
Point-to-Point Protocol over Ethernet PPPoE or PPPoE
PPPoE is a well-defined communication mechanism between the client and the server. In the RAR implementation, radio takes
the role of the PPPoE client and router takes the role of the PPPoE server. This allows a loose coupling of radio and router,
while providing a well-defined and predictable communication mechanism.
As PPPoE is a session or a connection oriented protocol, it extends the point-to-point radio frequency (RF) link from an external
radio to an IOS router.
PPPoE extensions are used when the router communicates with the radio. In the Cisco IOS implementation of PPPoE, each individual
session is represented by virtual access interface (connectivity to a radio neighbor) on which, QoS can be applied with these
RFC5578 provides extensions to PPPoE to support credit-based flow control and session-based real time link metrics, which
are very useful for connections with variable bandwidth and limited buffering capabilities (such as radio links).
Virtual Multipoint Interface (VMI)
Though PPPoE Extensions provides the most of the setup to communicate between a router and a radio, VMI addresses the need
to manage and translate events that higher layers (example, routing protocols) consume. In addition, VMI operates in the Bypass
In Bypass mode, every Virtual Access Interface (VAI) representing a radio neighbor is exposed to routing protocols OSPFv3
and EIGRP, so that, the routing protocol directly communicates with the respective VAI for both unicast and multicast routing
In Aggregate mode, VMI is exposed to the routing protocols (OSPF) so that the routing protocols can leverage VMI for their
optimum efficiency. When the network neighbors are viewed as a collection of networks on a point-to-multipoint link with broadcast
and multicast capability at VMI, VMI helps in aggregating the multiple virtual access interfaces created from PPPoE. VMI presents
a single multi access layer 2 broadcast capable interface. The VMI layer handles re-directs unicast routing protocol traffic
to the appropriate P2P link (Virtual-Access interface), and replicats any Multicast/Broadcast traffic that needs to flow.
Since the routing protocol communicates to a single interface, the size of the topology database is reduced, without impacting
the integrity of the network.