The Aloha Protocol is a layer 2 (Layer 2 is the Data Link layer of the OSI model) protocol for LAN networks with broadcast topology. It was used for the first time in the Packet Radio System of the University of Hawaii in 1970. It is a predecessor to the Ethernet. There are two versions of Aloha, Pure Aloha and Slotted Aloha. The Open Systems Interconnection Reference Model (OSI Model or OSI Reference Model for short) is a layered abstract description for communications and computer network protocol design, developed as part of the Open Systems Interconnect initiative. ... The Open Systems Interconnection Reference Model (OSI Model or OSI Reference Model for short) is a layered abstract description for communications and computer network protocol design, developed as part of the Open Systems Interconnect initiative. ... A local area network (LAN) is a computer network covering a local area, like a home, office or small group of buildings such as a college. ... A way Amateur or Ham radio operators use to communicate with computers over radio-frenquency links. ... Ethernet (this name comes from the physical concept of ether) is a frame-based computer networking technology for local area networks (LANs). ...

Pure Aloha

In Pure Aloha, any station can begin to send at any time, without listening to the medium first. Thus many collisions occur, and throughput decreases when too many stations are attached to the network.

If the packet transmission time is T, then vulnerable period of pure aloha is 2T.

Maximum throughput is 18% of physical channel capacity In the business management theory of constraints, throughput is the rate at which a system produces money, in contrast to output, which may be sold or stored in a warehouse. ...

Slotted Aloha

An improvement to the original Aloha protocol was Slotted Aloha, which introduced discrete timeslots. A station can not send anytime, but just at the beginning of a timeslot, and thus collisions are reduced.

If the packet transmission time is T, then vulnerable period of slotted aloha is T.

The maximum utilization of the bandwith is 37 %.

Because Listen before send, as used in the Ethernet, works a lot better than Aloha, Slotted Aloha is now only used on low band width tactical SATCOM networks by the US Military.