CSMA persistence
A carrier-sense/multiple-access transmission strategy is said to be nonpersistent if, when the line is busy, the sender waits a randomly selected time. A strategy is p-persistent if, after waiting for…
Errors
Packets can have bits flipped or garbled by electrical noise on the cable; estimates of the frequency with which this occurs range from 1 in 104 to 1 in 106 .…
Hubs and topology
Ethernet hubs (multiport repeaters) change the topology, but not the fundamental constraints. Hubs enabled the model in which each station now had its own link to the wiring closet. Loops…
Capture effect
The capture effect is a scenario illustrating the potential lack of fairness in the exponential backoff algorithm. The unswitched Ethernet must be fully busy, in that each of two senders…
Exponential Backoff Algorithm
Whenever there is a collision the exponential backoff algorithm – operating at the MAC layer – is used to determine when each station will retry its transmission. Backoff here is…
Ethernet delay budget
The total here is 220 bits; in a full accounting it would be 232. Some of the numbers shown are a little high, but there are also signal rise time…
The Slot Time and Collisions
The diameter of an Ethernet is the maximum distance between any pair of stations. The actual total length of cable can be much greater than this, if, for example, the…
The LAN Layer
The LAN layer, at its upper end, supplies to the network layer a mechanism for addressing a packet and sending it from one station to another. At its lower end,…
Ethernet Address Internal Structure
The second-to-lowest-order bit of a physical Ethernet address indicates whether that address is believed to be globally unique or if it is only locally unique; this is known as the…
Ethernet Multicast
Another category of Ethernet addresses is multicast, used to transmit to a set of stations; streaming video to multiple simultaneous viewers might use Ethernet multicast. The lowest-order bit in the…
