What does it mean when it says a wired link of 1Gbps?

[xenonn]

When we say a wired link of 1Gbps, do we mean the wire link will transfer 1Gbits of data from Point A to Point B every one second?

If this is true, then this is kind of weird because there is this propagation time that determines the time taken for the bits to travel from Point A to Point B? Also, if this is the case, then say Point A sends a packet of 2Gbits of data and Point B will receive it in 2 seconds time?

If this isn't true, then what exactly does it mean to have a link that has 1Gbps?

Thanks.

 

[mxsix]

It means your computer has a 10/100/1000(Gigabit) LAN controller and that it's plugged in to a switch/router/etc that also supports 1Gbps. Gigabit ethernet is capable of transferring 1 billion bits per second (gigabit) from one host to another. Keep in mind those are *perfect world* results. You can get near those speeds but in theory they will be somewhat skewed depending on network traffic and many other factors. But you have it fundamentally down, on a Gigabit line, it would take 2 seconds (roughly) to send 2 billion bits.

 

[Catsrules]

When we say a wired link of 1Gbps, do we mean the wire link will transfer 1Gbits of data from Point A to Point B every one second?

If this is true, then this is kind of weird because there is this propagation time that determines the time taken for the bits to travel from Point A to Point B? Also, if this is the case, then say Point A sends a packet of 2Gbits of data and Point B will receive it in 2 seconds time?

If this isn't true, then what exactly does it mean to have a link that has 1Gbps?

Thanks.

It is saying that is the max speed it can transfer data between the computer and the device it is connected to. But very very rarely will you actually see the full speeds because, you also need to take in to account other devices that are in use that can't go that fast. Like Hard drive, USB, maybe the device you are talking to is only 100MBps, stuff like that.
I have only been able to active these speeds after I partition a part of my RAM memory on two computer and copied a file between them directly to the ram.
You probably could do it will two SSD in two gigabit capable computers
Sorta like a car, my car could probably go 120Mph, but I have other cars in the way, bad roads, turns in the road, traffic law weather, that prevent me from ever achieving the full speed my car is capable of.

 

[xenonn]

Thanks for the answers. Then if this 1Gbps link does tell the speed of the link, then why often there is another delay considered, the propagation time, that tells the time taken to transfer the packet of bits from Point A to Point B?

Since the 1Gbps already defines the theoretical speed, then wouldn't the time taken to transfer from Point A to Point B straightforwardly be L/(1x10^9) seconds where L is the bits size of a packet? But this isn't the case because when I read the books it appears to me that the time taken to completely transfer from Point A to Point B is the so called propagation time and is independent the 1Gbps rate.

I'm still confused.

 

[mxsix]

When computers send data over a network, they don't just send the raw data out because none of the hardware would know what to do with it.

Picture it like mailing a letter. You don't just write a letter and drop it off at the post office. They would have no idea where to send it. So every piece of data a computer sends out has to be enveloped (pun) inside of a "packet". These packets carry data like an address of where the data is going, etc. These packets take up data and have to fit the original data along with them. So if you are sending a very large file over a network, the computer has to break up each piece into a packet and then transfer it. Those packets create a sizeable increase in the size of data you are sending.

 

[xenonn]

Let's have a scenario. Suppose I have a packet of size 5kbits and will be transferred from Point A to Router C first through a link of 1Gbps. The transfer time for the packet will be 5kbits/1Gbps=5*10^(-6) seconds or 1/20000 seconds. And here's a visualisation:

However, from the picture above, Router C does not receive the whole packet after 1/20000 seconds. Router C only receives it after the propagation time, which depends on the signal speed. And here's the confusion: so the time taken to transfer from Point A to Router C is not at 1Gigabit per second despite the link has a capacity of 1Gbps?

The transmission time in this case is 1/20000 seconds but what is happening during this transmission time since this transmission time doesn't look like it is transferring the bits from Point A to Router C?

 

[mxsix]

In networking, there are many types of delays before a computer can send out/receive a packet. See this article for the different types: http://en.wikipedia.org/wiki/Network_delay

To answer your confusion: The medium is in fact 1Gbps. That propagation delay you see is actually extremely negligible. The diagram you provided is just a way to visualize it. Here is a great example sheet with answers to help you more:
http://www.cs.ucsb.edu/~sudipto/TA/cs176a/Example_problems.pdf

 

[xenonn]

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