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Non-broadcast Multiple Access (NBMA) refers to a computer network to which several hosts are connected. However, the data are transmitted only directly from one computer to another single host across a switched fabric or over a virtual circuit. NBMA networks support broadcast or multicast traffic manually.
There are four network types in Open Shortest Path First (OSPF) communication protocol:
NBMA networks work opposite of broadcast networks.
In broadcast networks, various computers as well as other devices are connected to a shared network cable or other medium. When a computer sends frames, each node on the network listens to the frames; however, only the node to which the frames are sent receives the frames. Hence, the frames are broadcast.
NBMA is mainly employed on networks that do not have broadcast or multicast capabilities. Frame Relay, Asynchronous Transfer Mode (ATM), home power line networking, and X.25 are some common examples of NBMA network technologies.
In NBMA networks, a technique known as split horizon route advertisement should be implemented by distance-vector routing protocols to prevent routing loops. This protocol family depends on link layer broadcasting to enable route advertisement propagation.
Therefore, if this feature is absent, it should be emulated with a series of unicast transmissions; however, this may lead to receiver node transmitting a route advertisement straight back to the node from where it has just received the same.
Next Hop Resolution Protocol (NHRP) is employed to find the NBMA subnetwork addresses of the NBMA next hop towards a public inter-networking layer address.