Where does packet collide?

A formatted unit of data carried by a packet-switched network: a message is chopped into standardized blocks, and each block wraps its payload in a header that records the source, the destination, and its place in sequence, so every block can be routed across the network on its own rather than following one reserved line. Baran's 1964 On Distributed Communications Networks set out this design, dividing traffic into uniform message blocks that hop independently between nodes and are reassembled at the far end, the scheme later called packet switching that underlies the internet. The referent is a self-contained bundle of bits moving through a network, defined by its header and payload, not a localized burst of quantum waves nor a discharged quantum of neurotransmitter.[1]

Unit

One header-plus-payload block of data, routed and reassembled on its own

Recovery means

Lost or corrupted blocks are detected by a checksum and recovered by asking for retransmission

Measured by

Measured by size in bytes, by its header fields, and by network statistics such as loss, latency, and jitter

A localized burst of waves built by adding together many waves of different frequencies so that they reinforce in one small region and cancel elsewhere: such a wave packet can stand for a particle whose position and momentum are both narrowed, and the spread it must keep in each is the content of the uncertainty relation. Schrödinger's 1926 Der stetige Übergang von der Mikro- zur Makromechanik constructed a packet from oscillator wavefunctions and showed it could stay compact and move like a classical particle, the origin of the Gaussian wave packet. The referent is a concentrated solution of a wave equation standing for a quantum particle, not a block of data routed through a network nor a quantum of transmitter released at a synapse.[2]

Unit

One concentrated wave-equation solution, spread across position and momentum

Recovery means

A free packet gradually spreads over time as its component waves travel at slightly different speeds

Measured by

Characterized by its width in position and in momentum, whose product is bounded below by the uncertainty relation

The discrete quantum of neurotransmitter released as a single unit when one synaptic vesicle empties into the gap between neurons: the electrical response at the muscle does not rise smoothly but climbs in equal steps, as if assembled from many identical small packets, each the fixed content of one vesicle. Del Castillo and Katz's 1954 Quantal components of the end-plate potential showed that the response is made of whole-number multiples of one elementary packet, the basis of the quantal theory of synaptic transmission. The referent is a fixed bundle of signalling molecules discharged at a synapse, not a unit of data crossing a network nor a localized quantum wave.[3]

Unit

One vesicle's worth of transmitter, the elementary quantum of release

Recovery means

The emptied vesicle is recovered by the terminal and refilled with transmitter for later release

Measured by

Inferred from the step size and the statistics of miniature and evoked end-plate potentials