As Yeastar wants to use their appliances not only in very small businesses, I would like to put a few design considerations out here for discussion / comments, based on what I see other vendors do. This is for future products, of course:
19" form factor to be rack mounted (P560+570 cover that already). Even very small organizations have 19" network cabinets these days, so even very small appliance models could be offered in 19" form factor (unless that drives the price up too much - but a 10-20 extension PBX for under $200 in a rack-mountable appliance would be nice).
Locked power cords (see below for a picture how Ubiquiti handles that with their rackmounted Unifi products). That way, nobody can accidentally cut power from the PBX when working in the rack.
Dual redundant power supplies. I think all professional gear has that anyways.
- Other than power, no other ports on the back! When a PBX is rack mounted, all ports such as LAN or WAN and all LEDs and all buttons (incl. reset button hole) and all card slots etc. need to be at the front! I am unsure about the Antenna ports (may be someone else here has some insight on that one)
- May be a front mounted mini touch display showing the most important KPIs and stats (that also allows to set / change the IP address during the initial setup) could be useful. Again, see a screenshot of the current rack-mounted network equipment from Ubiquiti that has that. I personally think that's more a "nice to have", but I know others who disagree and find this very useful.
- At least the higher models should have a redundant storage system (RAID-1), not just a single memory card / chip / SSD.
The use of LED colors needs to carry common meaning. RED should be reserved for errors only (especially blinking red should be for critical errors). Green and Blue can be used to display status information. On Amber I am torn as Switches use Amber to show status information as well (e.g. 100MBit connections = Amber, 1000MBit connection = green), and flashing of those LEDs is used to show activity. But I am pretty certain RED (and especially blinking red) should be reserved exclusively for errors and critical errors. Right now, red is used to convey the status of expansion modules, and I think it is not a good idea. When a technician looks into a 19" rack and sees solid or blinking red, that indicates a problem. So I think Yeastar should re-work their status LED scheme accordingly.
- At least the larger models should use ECC RAM (and a CPU that supports ECC RAM). All Servers and Workstations use that for good reason, so Appliances should, too.
Active/Active failover mechanism. Especially companies that need a reliable PBX insist on having a PBX that keeps working seamlessly even when an appliance suffers a fatal defect. That is why they would always want to deploy at least 2 of those boxes, and have them configured and interconnected in a way that a seamless failover happens automatically and swiftly.
Graceful shutdown via SNMP (even through a trap from a UPS). The Yeastar documentation is very clear that an appliance should not just shut down by pulling the power cord. Instead, it must be shut down gracefully in order to prevent corrupted files and an invalid state. When power fails, a UPS battery will certainly be in place in most organizations to cover brief outages. But when these outages last, all UPS battery backup systems I know will trigger SNMP messages that can be used by the PBX appliance directly (or through a Network Management System) to gracefully shut down before power fails entirely.
Logging. The PBX should clearly differentiate between system logs, event logs, audit logs, and security logs at least. It should be possible to not only save & view & download those logs from the PBX UI, but also send them to a remote log management system such as Splunk or Graylog or an ELK stack in a way that the operator can clearly distinguish between the different logs. Also, each log record needs to start with a timestamp as per ISO 8601 with date, time, and timezone.
- Strict implementation of Security best practices. Standards such as NIST and OWASP (and many others) provide comprehensive frameworks on things like password management, certificate management, patch management, robust design of user interfaces, access control, encryption of data at rest and in transit, key management, protection of APIs, and many others. All organizations I have ever worked for perform a risk assessment before allowing ANY new software or appliance product into their infrastructure. And the implementation of these security best practices but also resiliency, high availability, disaster recoverability etc. are ALWAYS factors in such assessments. I am not sure any of the Yeastar products would pass such a test yet.
I am sure there's more to consider for future appliance engineering projects, but these things were the ones that came to mind when I watched the videos on the P550, 560, and 570.