Editing Slot time

{{Short description|Time it takes to send a designated amount of data from one network host to another}}
{{See also|bit time}}
{{Use American English|date = March 2019}}

'''Slot time''' is a concept in [[computer network]]ing. It is at least twice the time it takes for an electronic pulse ([[OSI model|OSI]] [[Physical layer|Layer 1 - Physical]]) to travel the length of the maximum theoretical distance between two nodes. In [[CSMA/CD]] networks such as [[Ethernet]], the slot time is an upper limit on the acquisition of the medium, a limit on the length of a packet fragment generated by a collision, and the scheduling quantum for retransmission.<ref>IEEE 802.3 ''4.2.3.2.3 Collision handling''</ref>

Since a pulse's runtime will never exceed '''slot time''' (the maximum theoretical time for a frame to travel a network), the [[network interface controller]], or NIC waits a minimum of slot time before retransmitting after a collision happened, in order to allow any pulse that was initiated at the time that the waiting NIC was requested to send, to reach all other nodes. By allowing the pulse to reach the waiting NIC, a [[local collision]] occurs (i.e. while still sending) rather than a [[late collision]] occurring (after sending may or may not have ended). By having the collision occur at the NIC (local) and not on the wire (late) CSMA/CD implementation recover the situation by retransmitting later.

Some times for Ethernet slot time include:<ref>IEEE 802.3 ''4.4.2 MAC parameters''</ref>

{|class="wikitable"
!Speed
!Slot time<ref>Slot time is only applicable to [[duplex (telecommunications)|half-duplex]] transmissions. Since slot time is the time required to wait for the medium to be free from transmissions, there is no time required to wait for [[duplex (telecommunications)|full-duplex]] transmissions. 1&nbsp;Gbit/s (in practice) and faster (by standard) are full duplex technologies, so slot time is not applicable here.</ref>
!Time Interval
|-
|10 Mbit/s
|512 bit times
|51.2 microseconds
|-
|100 Mbit/s
|512 bit times
|5.12 microseconds
|-
|1 Gbit/s<ref>theoretical, only full-duplex devices exist</ref>
|4096 bit times
|4.096 microseconds
|-
|2.5 Gbit/s onward
|colspan=2 style="text-align: center" | no half-duplex operation
|}
''See [[DCF Interframe Space|DIFS]] for information on 802.11x slot times.''

==References==
{{Reflist}}

[[Category:Ethernet]]
[[Category:Computer network analysis]]


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