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Sorry if this seems to be a stupid question, I'm not sure how to specify what I want to know when checking google.

I will have 2 or 3 devices pumping out data on a 100Base-T port. The combined data rate of all devices is about 15MB/S which exceeds the optimal 100Base-T channel capacity (12MB/S), but well within the realms of a 1000Base-T connection. Each device will be sending a burst of data in the form of an FTP transfer to a common, single host computer in a sequential manner ie:

  1. Device A establishes FTP connection and transfers data
  2. Device B establishes FTP connection and transfers data
  3. Device C establishes FTP connection and transfers data

It may be that the A&B, B&C and C&A transfers overlap in the time domain to some extent.

There will be minimal traffic going back from the computer to each device (in general what ever is needed to support the FTP transfers), and the network will be dedicated to transferring data between these devices and the host computer.

Is it possible to use a switch to combine the multiple incoming 100Base-T streams into a single outgoing 1000Base-T stream? if so what features in a switch should I be looking for?

Or would it be better to have 3 physical point-to-point 100Base-T dedicated connections between each device and the host computer? (thus having at least 3 physical Ethernet interfaces on that computer)

Note that I can't change the interface on the devices, but I am free to choose the network and host computer configuration.

Thanks for you help


Edit Oops .. I meant MB/S not KB/S

Edit 2 I should have mentioned that all the devices and the host computer will be in close proximity - IE easily within a single Ethernet run length.

Edit 3

This is where I start pounding my head against the wall. The back story is that I am involved in a project where the device generates the data which is sent to the computer where it is collated and saved. My part is the computer backend and overall UI and display - not the generating device. Last week I saw that they were specifying 1 single device and trying to get it to pump out 15MB/S over a single 100Base-T port. I pointed out that they would need to break the laws of physics to achieve this. The problem could be parallelized by adding up to 5 more devices in order to bring the peak data rate on any single 100Base-T link to well below that links maximum throughput. This question was part of my research into how the system could be configured and still keep things in the current version of reality. I have since learnt that there is no money in the budget for additional devices. Thus the question is now moot. I have yet to see how they intend to meet requirements with only a single device. Its not really my problem, but it also does not bode well for the quality of computer they bought which will form the basis of the work I will be doing.

And yes I do read TDWTF

Thank-you to everybody who contributed to the discussion

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up vote 2 down vote accepted

While what Warner said will work, I just don't see the benefit of NIC aggregation in this scenario as the sending devices are only at 100Base-T (~12MB/s), whereas any old SMB/SOHO GbE switch's backplane/port/wire speed is going to be more than capable to handle even three concurrent 100Base-T transfers.

If you're experiencing poor performance now, I'd be looking at the host sub-system (disk I/O, etc.) first and would recommend using IPerf to test throughput before buying or changing anything.

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We don't have poor performance now. What we have is a design on paper where someone proposed a single device trying to push out 15MB/S onto a single 100Base-T line. The problem is physically parallelizable to multiple devices so I am exploring network topologies that support the desired data transfer. I'm not sold on the aggregation either given the proximity of the devices. – Peter M Jun 14 '10 at 16:48
Gravyface has it right, just pop a cheap gigabit switch into the mix. As long at the destination support GigE (and can actually handle that much data), all 3 sources could be sending at the same time and it wouldn't be bottlenecked. – Chris S Jun 14 '10 at 16:55
Peter M: aggregation is useful when your network exceeds the throughput of your NIC, but in your case, the sending devices are the limiting factor in the equation (or possible host I/O as I've suggested). No unique topology or design considerations are needed in your case; just a simple star topology will work well with a good quality GbE switch (or even a 4x10/100 with a 1 GbE uplink, but you don't see those as often in small switches nowadays). – gravyface Jun 14 '10 at 17:38
To clarify, if your sending devices had GbE NICs, and you had a GbE switch with 10GbE uplinks (or two 1 GbE uplinks trunked) then NIC teaming two GbE on the host would be a smart idea. – gravyface Jun 14 '10 at 17:44
@gravyface - This is off topic, but what happens to packets sent in the other direction from the 1000Base-T side. If they cannot be absorbed by the 100Base-T side, does the switch drop them? Or is there buffering for a couple of packets in order to smooth out bursts of data? Eventually there will come a point where the 1000Base-T over whelms the 100Base-T – Peter M Jun 14 '10 at 18:22

100Base-T connections are capable of 12.5MB a second. I have no idea where you are getting 12KB from.

You are looking for link aggregation, which is otherwise known as NIC bonding or teaming. This is supported in most operating systems.

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Why would he need link aggregation? He talks about 3 different devices, not interfaces. – jishi Jun 14 '10 at 14:33
I agree with jishi: his bottleneck at this point is either the host machine's I/O subsystem or the three transmitting data devices' 10/100 NICs. NIC bonding achieves nothing here. – gravyface Jun 14 '10 at 14:49
"Each device will be sending a burst of data in the form of an FTP transfer to a common, single host computer in a sequential manner" -- seems like a candidate for bonding to me. – Warner Jun 14 '10 at 15:26
Oops .. as per my edit I meant 15MB/S – Peter M Jun 14 '10 at 16:33
@Warner - I just read up on the link you posted. Are you suggesting that my 3 devices hook into a switch that bonds them together to a single outgoing line? Given that the devices will be in proximity to the host computer, is there any advantage over 3 separate nics in that computer? – Peter M Jun 14 '10 at 16:43

Shouldn't a regular switch should be able to utilize 3 different 100Mbit devices to a single 1000Mbit device, and therefor maximizing the throughput to a total of 300Mbit? As long as the switch can handle the load.

I don't see why it would restrict the total bandwidth to anything less than 1 Gbit, that's the whole point with a full-featured layer-2 switch IIRC.

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This is why I asking the question. I have in the back of my mind that such a setup will negotiate the overall network to the lowest component speed. This may be true for a dumb hub, so I want to know what I need to specify in a higher quality device in order to get a setup that works. – Peter M Jun 14 '10 at 16:39
The network as a whole is not limited by individual connections. This wasn't true for hubs, not true for switches now. You'd have to go back to something like thin-net or tokenring to find problems like that. – Chris S Jun 14 '10 at 16:57
A switch won't have this problem - provide the common target device supports Gigabit Ethernet the switch will allow two, three or more slower 100Meg devices to send to it concurrently with capacity to spare. This is a common aggregation layer switch function - multiple slower (e.g. 100Meg) connections feeding into a smaller number of faster backbone\uplinks (e.g. Gigabit). Each link's speed is negotiated between itself and the switch port and doesn't affect anything else. – Helvick Jun 14 '10 at 16:58

Yes, a switch do what you are trying to accomplish with NO extra configuration.

If you have a gigabit switch and 4 devices connected to it: - server w/ 1 x 1Gbps connection - 3 x devices w/ 1 x 100Mbps connection

The server will be able to communicate with each of the devices at its line rate (100Mbps) without any special configuration or changes.

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