peer

A unit of communications hardware or software that is on the

same protocol layer of a network as another. A common way

of viewing a communications link is as two protocol stacks,

which are actually connected only at the very lowest

(physical) layer, but can be regarded as being connected at

each higher layer by virtue of the services provided by the

lower layers. Peer-to-peer communication refers to these real

or virtual connections between corresponding systems in each

layer.

To give a simple example, when two people talk to each other,

the lowest layer is the physical layer which concerns the

sound pressure waves travelling from mouth to ear (so mouths

and ears are peers) the next layer might be the speech and

hearing centres in the people's brains and the top layer their

cerebellums or minds. Although, barring telepathy, nothing

passes directly between the two minds, there is a peer-to-peer

communication between them.