# Network Cable Flow Rate vs Propagation Speed

I was reading about network Cables then I saw some information that made me feel confused for example : if we say have a we have copper wire (e.g. Twisted pair) that can achieve a flow rate of 10 Mbps , does that mean that the speed of the cable is 10 Mbps which implies that it can send 10 Mega bits of data from the source to the destination every one second ? or does this number mean that every one second this cable can hold data of 10 Mega bits in other words it is like 10 Mega bits can travel inside the cable at the same time (i.e. capacity )

then I passed through a term called "Propagation Speed " which is 2 * 10^8 m/s in copper wires , so what is the relation between the two terms ?

Any explanation that includes example would be very helpful

P.S: Sorry for my bad English

Regards

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## 2 Answers

Propagation speed - the speed which electrons flow through a copper cable - is about 0.6c.

Flow rate is a vague term. Perhaps you mean data rate or clock rate. That is the rate that bits can be transmitted on the link. While the type of cable can affect the maximum data rate, it's usually set by the network hardware.

Ethernet's nominal speed is what's used at the top of the physical layer - it includes all common signaling like the preamble, start-of-frame (SOF), and inter-packet gap (IPG) but excludes the actual line code (which may be as much as twice as high). So, for Classic Ethernet at 10 Mbit/s, you can send or receive 10 Mbit per second minus the overhead (38 byte per frame with a maximum payload of 1500 bytes).

Note that the actually usable data rate depends on many more factors. The signaling rate is just the rate between two connected network ports.

The bits that are actually on the wire depend on the signaling rate and the propagation speed of the wire. With a velocity factor of .64 for Cat. 5 cable, there's a propagation delay of 52.1 nanoseconds per 10 m, equivalent to .5 bits at 10 Mbit/s or 52 bits at 1 Gbit/s.

For a cable to hold a full second worth of data it would need to be .67 x c = 200,000 km which is way too long for copper and much too long for fiber as well.