What is the startup time of UbiSwitch BB-UBS-A-1?

– Copied from customer query –

What would be the startup time after voltage has been applied?

The startup time of BB-UBS-A-1 is less than 100ms. This doesn’t include the autonegotiation time for UbiSwitch to achieve link up with any connected device parts, which can range from 1-10 seconds, but this would be the case with any ethernet device (unless you bypass autonegotiation).

– Copied from customer email –

Thank you, what is the worst case latency or port to port?

That’s a straightforward question but it doesn’t have a straightforward answer :slight_smile:

Latency in a switch is highly dependent on the network conditions on all the ports in the switch. In the simplest case, let’s say you have two devices wanting to exchange data. Device A wants to send data directly to Device B, which is currently not receiving anything. Both devices are at the same data rate (let’s say, 1Gbps). In such a simple case, the latency will be minimal, dictated purely by the transit time inside the switch, the copper traces, and the wiring. Realistically it’s likely to have a latency of less than 100ns.

However in a more complex case where there is a network overload, packets can be dropped and thus the latency is infinite. Imagine a situation where three devices (devices A, B and C) are trying to send at 1Gbps into a single device (device D). The switch will have to buffer packets from the three devices because device D can only receive at 1Gbps. Eventually the switch’s internal packet buffer (which is 2Mbits for UbiSwitch) will overflow and packets will be lost. Note that this is not an issue specific to UbiSwitch, but a fundamental limitation of any ethernet switch. To solve such a problem, you might elect to connect device D to a 10Gbps port on UbiSwitch, which would allow the switch to send all three streams at 1Gbps into the 10Gbps link without any packet loss.

To answer your question, however, I think you’re asking “what is a realistic latency I might expect to see on a network that is busy but not overloaded?”. Of course, this question is still somewhat undefined (how long is a piece of string?), but to give a very general answer, you might expect to see around 10uS of latency before you start seeing packet loss.

Your question indicates you care about latency in your application. There are tools and techniques within the ethernet standard that can be used to improve latency and determinism of ethernet. If you share a little more about your timing/latency/criticality requirements, we may be able to suggest a technology that UbiSwitch can implement to help.