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Ethernet performance

Due to the non-deterministic access procedure ofEthernetCSMA/ CD, all stations connected to an Ethernet have equal rights. This means that the probability of collisions increases with the number of stations connected and ready to transmit, with the frame length and with the length of the corresponding LAN segments.

In fact, as the segment length increases, the propagation time between the two stations farthest from each other increases, which has a negative effect on the time required to detect a collision. All three parameters, the number of stations, the frame length and the segment length determine the performance limit of CSMA/CD networks. The shorter the frame length and the higher the number of stations ready to transmit, the lower their efficiency becomes.

Relative performance of shared and switched Ethernet

Relative performance of shared and switched Ethernet

The frame length of the CSMA/CD frame affects the performance in that the ratio of payload to frame length becomes lower as the frame size becomes smaller.

Channel efficiencies of Ethernet at different data packet lengths.

Channel efficiencies of Ethernet at different data packet lengths.

The frame length is limited in its basic values: The maximum block length is 1,518 bytes, and the minimum is 64 bytes. This means that with a frame length of 64 bytes and the maximum possible ready-to-send station count of 256 Ethernet has the lowest efficiency.

With the switched Ethernet, the performance increases by quite a bit compared to the shared Ethernet versions. If the performance of the classic Ethernet (10Base..) is set to 1, then the shared variants of 100-Mbit/s Ethernet are ten times the value and the 1000-Mbit/s variants are twenty to ninety times the value, depending on the frame length. The switched variants, on the other hand, achieve these values on a port basis.

Informations:
Englisch: Ethernet performance
Updated at: 18.11.2013
#Words: 279
Links: procedure, call deflection (ETSI) (CD), Ethernet, frame, local area network (LAN)
Translations: DE
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