Download speed and ping suffers during PC to PC file copy

Question

Why does the ping and internet download speed suffer on PC#1 when files copied from PC#1 to PC#2?

During file copy, my ping goes from 20ms to 600ms+, Download speed goes from 1.8MB/S to 250 KB/S give or take.

I am downloading files On PC#1_Drive#C and PC#2 is copying files from PC#1_Drive#D. So it is not the hard drive perhaps.

My network looks like this and in a house where a main line goes to a room and if there are multiple devices I have installed a switch. While far from perfect the network has "evolved". I hope I have represented the basic network well enough.

DSL Router <-> 1Gb Switch#1 <-> PC#1 (1Gb Network card) "The Office"

1Gb Switch#1 <-> 1Gb Switch#Central <-> 1Gb Switch#2 "The Central Room"

1Gb Switch#2 -> PC#2 (100Mb Network Card) "The Lounge"

(All cable is Cat6)

Why is there a speed difference? How can I determine the problem?

AFAIK, the switches do not need to be in any particular port. When PC#2 is copying files using a network path past PC#1 (if you can call it that way), to PC#3. PC#1 does not have a speed issue.

Answer 1

Let's use an analogy. The network is like a railroad. Trains can only go in one direction at a time (since there is only one track) and only a limited amount of cars (data packets) can be moved by each engine.

Copying a file from PC1 to PC2 involves moving the data and returning an ACK signal to indicate that there were no errors in the transfer.

When you download a file from the internet to PC1, you again have 2 way communication.

The one problem is the collisions that happen when PC1 sends a data package when a package arrives from the internet. Since the information is stacked on top of each other, the receiving computers ignore the data (since it is not understood). After a time, since an ACK signal was not received, the data is resent. Your data speed drops because of the traffic on the network.