Speed and rate of data transfer

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Discussion Overview

The discussion revolves around the challenges of transferring digital signals over a 100-meter wire at a speed of 1000 Mbps. Participants explore the implications of signal timing, potential issues with signal integrity, and the necessity of using specific transmission techniques or standards.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Exploratory

Main Points Raised

  • One participant questions whether signals can change states quickly enough to reach the end of a 100-meter wire, particularly with alternating sequences like 01010101.
  • Another participant asserts that multiple bits can travel simultaneously in a wire, provided they maintain a similar velocity, although dispersion may affect signal quality over longer distances.
  • Some participants mention that achieving high bit rates requires quality components and adherence to standards, referencing Ethernet specifications as a guideline.
  • Concerns are raised about the worst-case scenarios for signal transmission, suggesting that long sequences of identical bits could lead to issues with signal detection due to the properties of transmission lines.
  • One participant introduces the concept of Return to Zero (RTZ) coding, such as Manchester encoding, to mitigate issues with long sequences of bits, although this approach may require more bandwidth.
  • Another participant discusses the possibility of sending narrow pulses down a wire, comparing it to radar technology, and challenges the notion that a potential difference must be maintained throughout the transmission.
  • There is a debate about the necessity of optical fiber for higher data rates, with one participant questioning the feasibility of sending high-frequency signals over traditional copper wires.

Areas of Agreement / Disagreement

Participants express differing views on the feasibility and methods of transmitting high-speed digital signals over a wire. There is no consensus on the best approach or the fundamental mechanics of signal transmission in this context.

Contextual Notes

Participants reference various standards and technologies, indicating that the discussion is influenced by practical considerations such as signal degradation, the effects of transmission line properties, and the limitations of different wiring types.

  • #31
the_emi_guy said:
On the topic of latency of data communications links here are some stats you may find interesting:

At 100 gigabit Ethernet, the spacing between bits on the fiber optic cable is a mere 2mm.
A long reach (40Km) 100GBE link will contain 20 million bits in flight.
Corning Glass has shipped over 30 million Km of long haul (LEAF) fiber.

Thus, at any frozen moment in time, this corresponds to 15 terabits of data in flight within these cables.
There is a directly similar acoustic situation. When you shout at someone in the distance, your whole sentence may be hanging in the air, on its way to them after you close your mouth finally.
Latency is only a problem when synchronism is important. This can be on a circuit board where line lengths on a Bus need to be equalised to within a mm or two.
 

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