Gbit Topology question

[marc1968]

Hi guys, I have the following setup and I have some questions you might be able to help me with ( I hope )

consider the following :

left side of house 10/100 cable modem --> 10/100/1000 Netgear GS108 --> 3 media players 2 of which are 10/100, 1 10/100/1000 PC_1, 1 10/100 IPcam and another 10/100/1000 GS108 on the right side of the house.
This second 108 --> 10/100 Linksys WRT54GL acces point, a 10/100/1000 workstation_2, a 10/100 IP cam and QNAP 509 with 10/100/1000

So the left and right side of the house both have a GS108 which are connected to each other and a variety of 10/100 and Gbit devices

My questions :
1) if the QNAP is streaming to 1 of the 10/100 media players on the other side of the house will it drop the whole connection between the left and the right side of the house to 10/100 or will the connection between the 2 Gbit switches still be at 1000Mbit? So essentially : if i were to both stream a movie from NAS to a media player and copy files from eg PC_1 to the NAS would the latter only copy at 100Mbit speed because the link between the 2 switches is forced to 100Mb by the media player?

2)If any of the devices on the right side of the house have a VPN connection open to the 10/100 cable modem would this drop the whole connection between the 2 gs108's down to 100Mb because it forces the connection down to the cable modems networking speed.

so essentially : if 2 Gbit switches are linked will the connection between them always be at Gbit speed (even if they have to transfer to a 100Mb device) or will the whole link drop down to 100Mb as soon as 1 100Mb device uses that connection (so no Gbit transfers between those 2 GS108's when a 100Mb device is using the NAS eg)

Sorry if this is a newb question but i haven't been able to find an answer to this after a few hours of searching

 

[thiggins]

I assume that you have tried this since you have everything set up. What did your experiment tell you?

Link rates will be set by the devices that are plugged into ports. Performance is different and depends and many factors.

Give this article a read:

When Flow Control is not a Good Thing

 

[marc1968]

Sadly I haven't been able to try it since I am waiting for the RE3 drives for the NAS.

I hope the link does not go down to 100Mbit otherwise it will be impossible to stream more than 100Mbit/s from my new NAS (which is only 2 HD movies simultaneously). I was hoping to stream at least 200Mbit/s from that NAS. I Guess I will have to test myself once the drives arrive.

 

[thiggins]

You don't need to wait for the NAS. You could perform tests using the PCs.

The simple answer is that the gigabit connection between switches will stay at gigabit. But traffic for each client-to-client connection will move at a rate supported by the slowest member of a connection pair.

So the switch-to-switch bandwidth won't drop to 100Mbps. But if you have a 100 Mbps client and a gigabit client active with the same gigabit server at the same time, then you very well could see that gigabit client's throughput be limited, due to the flow control mechanism described in the link I gave in the previous response.

But if you had another pair of gigabit clients running through the same link, they would be unaffected by the other clients.