[Android Apps and Games] neutro_b:
As far as I can tell, Onkyo receivers have their own protocol called ISCP (for Integra Serial Communication Protocol). Used over ethernet or WiFi, each ISCP message takes the form of a TCP packet containing a specific message. The protocol is in constant evolution and proprietary to boot, but the power on / power off commands did not change in years. Basically the packet is simply:

Header: I S C P
Header Size: 0x00000010
Data Size: variable
Version: variable (0x01 for the 2011 protocol)
Reserved : 0x000000
Data: variable

The Data is:

Start Character: !
Destination Unit Type Character: 1 (for receivers)
ISCP Command: 3 characters, PWR for powering the main zone
ISCP parameter: variable (00 for power off, 01 for power on, QSTN for querying the power state)
End Character: this seems to depend on model, either [EOF], [EOF][CR] or [EOF][CR][LF]

Thus powering on the receiver is relatively simple but require that specific packet.

Here it is. Note that since I don't have 10 posts yet, I cannot include URLs, so I had to redact the URLs inside the description. They were replaced by ***. Also, I'm not sure I would trust any claimed capability from Onkyo: this receiver claims support for gapless playback but in reality it's not capable of gapless playback.

<root xmlns="urn:schemas-upnp-org:device-1-0">
<specVersion>
<major>1</major>
<minor>0</minor>
</specVersion>
<device>
<deviceType>urn:schemas-upnp-org:device:MediaRenderer:1</deviceType>
<friendlyName>TX-NR818</friendlyName>
<manufacturer>ONKYO</manufacturer>
<manufacturerURL>***</manufacturerURL>
<modelDescription>AV Receiver</modelDescription>
<modelName>TX-NR818</modelName>
<modelNumber>TX-NR818</modelNumber>
<modelURL>***</modelURL>
<UDN>uuid:0cb0b5e5-a2b5-e5b9-fbbc-e509a2b9ab12</UDN>
<serviceList>
<service>
<serviceType>urn:schemas-upnp-org:service:RenderingControl:1</serviceType>
<serviceId>urn:upnp-org:serviceId:RenderingControl</serviceId>
<controlURL>/upnp_control_0</controlURL>
<eventSubURL>/upnp_event_0</eventSubURL>
<SCPDURL>/scpd/RenderingControl_1</SCPDURL>
</service>
<service>
<serviceType>urn:schemas-upnp-org:service:ConnectionManager:1</serviceType>
<serviceId>urn:upnp-org:serviceId:ConnectionManager</serviceId>
<controlURL>/upnp_control_1</controlURL>
<eventSubURL>/upnp_event_1</eventSubURL>
<SCPDURL>/scpd/ConnectionManager_1</SCPDURL>
</service>
<service>
<serviceType>urn:schemas-upnp-org:service:AVTransport:1</serviceType>
<serviceId>urn:upnp-org:serviceId:AVTransport</serviceId>
<controlURL>/upnp_control_2</controlURL>
<eventSubURL>/upnp_event_2</eventSubURL>
<SCPDURL>/scpd/AVTransport_1</SCPDURL>
</service>
</serviceList>
<presentationURL>***</presentationURL>
<pnpx:X_hardwareId xmlns:pnpx="***">VEN_1666&DEV_1200&REV_01 VEN_0033&DEV_000C&REV_01</pnpx:X_hardwareId>
<dlna:X_DLNADOC xmlns:dlna="urn:schemas-dlna-org:device-1-0">DMR-1.50</dlna:X_DLNADOC>
<df:X_deviceCategory xmlns:df="***">Multimedia.DMR</df:X_deviceCategory>
<pnpx:X_compatibleId xmlns:pnpx="***">MS_DigitalMediaDeviceClass_DMR_V001</pnpx:X_compatibleId>
<iconList>
<icon>
<mimetype>image/jpeg</mimetype>
<width>120</width>
<height>120</height>
<depth>24</depth>
<url>***</url>
</icon>
<icon>
<mimetype>image/jpeg</mimetype>
<width>48</width>
<height>48</height>
<depth>24</depth>
<url>***</url>
</icon>
<icon>
<mimetype>image/jpeg</mimetype>
<width>32</width>
<height>32</height>
<depth>24</depth>
<url>***</url>
</icon>
<icon>
<mimetype>image/png</mimetype>
<width>120</width>
<height>120</height>
<depth>24</depth>
<url>***</url>
</icon>
<icon>
<mimetype>image/png</mimetype>
<width>48</width>
<height>48</height>
<depth>24</depth>
<url>***</url>
</icon>
<icon>
<mimetype>image/png</mimetype>
<width>32</width>
<height>32</height>
<depth>24</depth>
<url>***</url>
</icon>
</iconList>
<pnpx:X_deviceCategory xmlns:pnpx="http_schemas.microsoft.com/windows/pnpx/2005/11">MediaDevices</pnpx:X_deviceCategory>
<microsoft:magicPacketWakeSupported xmlns:microsoft="urn:schemas-microsoft-com:WMPNSS-1-0">0</microsoft:magicPacketWakeSupported>
<microsoft:X_magicPacketSendSupported xmlns:microsoft="urn:schemas-microsoft-com:WMPNSS-1-0">1</microsoft:X_magicPacketSendSupported>
</device>
</root>