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Sleep Proxy Property Encoding
The content of this site is taken from https://github.com/apple-oss-distributions/mDNSResponder/blob/main/mDNSCore/mDNSEmbeddedAPI.h
Sleep Proxy Servers are advertised using a structured service name, consisting of four metrics followed by a human-readable name. The metrics assist clients in deciding which Sleep Proxy Server(s) to use when multiple are available on the network. Each metric is a two-digit decimal number in the range 10-99. Lower metrics are generally better.
AA-BB-CC-DD.FF Name
Metrics:
- AA = Intent
- BB = Portability
- CC = Marginal Power
- DD = Total Power
- FF = Features Supported (Currently TCP Keepalive only)
20 = Dedicated Sleep Proxy Server -- a device, permanently powered on, installed for the express purpose of providing Sleep Proxy Service.
30 = Primary Network Infrastructure Hardware -- a router, DHCP server, NAT gateway, or similar permanently installed device which is permanently powered on. This is hardware designed for the express purpose of being network infrastructure, and for most home users is typically a single point of failure for the local network -- e.g. most home users only have a single NAT gateway / DHCP server. Even though in principle the hardware might technically be capable of running different software, a typical user is unlikely to do that. e.g. AirPort base station.
40 = Primary Network Infrastructure Software -- a general-purpose computer (e.g. Mac, Windows, Linux, etc.) which is currently running DHCP server or NAT gateway software, but the user could choose to turn that off fairly easily. e.g. iMac running Internet Sharing
50 = Secondary Network Infrastructure Hardware -- like primary infrastructure hardware, except not a single point of failure for the entire local network. For example, an AirPort base station in bridge mode. This may have clients associated with it, and if it goes away those clients will be inconvenienced, but unlike the NAT gateway / DHCP server, the entire local network is not dependent on it.
60 = Secondary Network Infrastructure Software -- like 50, but in a general- purpose CPU.
70 = Incidentally Available Hardware -- a device which has no power switch and is generally left powered on all the time. Even though it is not a part of what we conventionally consider network infrastructure (router, DHCP, NAT, DNS, etc.), and the rest of the network can operate fine without it, since it's available and unlikely to be turned off, it is a reasonable candidate for providing Sleep Proxy Service e.g. Apple TV, or an AirPort base station in client mode, associated with an existing wireless network (e.g. AirPort Express connected to a music system, or being used to share a USB printer).
80 = Incidentally Available Software -- a general-purpose computer which happens at this time to be set to "never sleep", and as such could be useful as a Sleep Proxy Server, but has not been intentionally provided for this purpose. Of all the Intent Metric categories this is the one most likely to be shut down or put to sleep without warning. However, if nothing else is availalable, it may be better than nothing. e.g. Office computer in the workplace which has been set to "never sleep"
Inversely related to mass of device, on the basis that, all other things being equal, heavier devices are less likely to be moved than lighter devices. E.g. A MacBook running Internet Sharing is probably more likely to be put to sleep and taken away than a Mac Pro running Internet Sharing. The Portability Metric is a logarithmic decibel scale, computed by taking the (approximate) mass of the device in milligrammes, taking the base 10 logarithm of that, multiplying by 10, and subtracting the result from 100:
Portability Metric = 100 - (log10(mg) * 10)
The Portability Metric is not necessarily computed literally from the actual mass of the device; the intent is just that lower numbers indicate more permanent devices, and higher numbers indicate devices more likely to be removed from the network, e.g., in order of increasing portability:
Mac Pro < iMac < Laptop < iPhone
Example values:
10 = 1 metric tonne
40 = 1kg
70 = 1g
90 = 10mg
The Marginal Power Metric is the power difference between sleeping and staying awake to be a Sleep Proxy Server.
The Total Power Metric is the total power consumption when being Sleep Proxy Server.
The Power Metrics use a logarithmic decibel scale, computed as ten times the base 10 logarithm of the (approximate) power in microwatts:
Power Metric = log10(uW) * 10
Higher values indicate higher power consumption. Example values:
10 = 10 uW
20 = 100 uW
30 = 1 mW
60 = 1 W
90 = 1 kW
1 = TCP KeepAlive supported