Impact of Higher Backbone Speed

[desweiler]

Hello,

let's take a look at this scenario. I have two Clients connected to a Switch each with a 1 Gig Link. The two Switches are connected via a 10Gig Link. Is the 10 Gig Link making the connection between the two Clients faster than having just a 1 Gig Link between the Switches?

Client--1 Gig--Switch---10 Gig----Switch---1Gig--Client

Or is it NOT making it any faster but instead only helps when more than one Client wants to transfer data?

I understand that each Link has a serialization delay.

So that is the time to put bits on the wire. So lets assume we want to put a single packet with 1500 bytes on the wire.

This would take 12 microseconds on 1 Gig.

This packet would fly through the wire at approximately 70-80% speed of light. It will eventually arrive at the first switch.

There it would be switched to the 10Gig link. This takes some latency that the switch needs for switching.

Then it will travel at the same speed as the 1 Gig link to the next switch because the propagation delay is independent of the bandwidth of the link.

At the second switch it is switched again with a certain latency.

Then it will travel the last path with the same speed again.

So total latency will be Serialization Delay of 1Gig link+2 times Switching latency+Propagation Delay of the whole path.

If this is correct then introducing the 10 Gig link between the switches does NOT speed up the transfer for one client pair. Is this correct?

[Joseph W. Doherty · Accepted solution]

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Posting

Or is it NOT making it any faster but instead only helps when more than one Client wants to transfer data?

Mostly.  The 10g link will reduce serialization delay for single frames, but won't help decrease time for the time to send multiple frames (except for the last).

If this is correct then introducing the 10 Gig link between the switches does NOT speed up the transfer for one client pair. Is this correct?

Yes (except for the last frame of a flow, as noted above).

[desweiler]

Does the switching latency include another serialization delay? So is there a serialization delay per Link?

Then for a store-and-forward switch one 1500 byte packet once arrived at the first switch would be sent out faster on the 10 gig interlink than on 1 gig correct? It then has to be buffered on the second switch until it arrived completely and then be sent out on the gig link. So would one 1500 byte frame be faster because of the shorter serialization delay on the switch interlink?

Why would a constant data stream not be faster? Because it needs to be buffered somewhere because of speed mismatches?

[Joseph W. Doherty]

Disclaimer

The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.

Liability Disclaimer

In no event shall Author be liable for any damages whatsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.

Posting

If the switch is doing store-and-forward, most of its latency will be serialization delay.

Yes, it takes less time to transmit a frame at 10g than 1g.

A constant stream (again, except the last frame) doesn't benefit from the 10g in-between link, because the frames are paced by the 1 gig link.