Can an android phone connect to both WiFi LAN (not necessarily connected to the Internet) and mobile data network at the same time? Or when it connects to one, does it have to disconnect from the other? My phone is Kyocera Hydro Icon with Android 4.4.2.
Multipath TCP is a relatively new technology that allows a device to use multiple network connections for the same logical TCP connection. This is used for mobile phones to use WiFi and mobile data connections at the same time to reduce the time for retrieving data.
I'm not sure which Android phones currently support multipath TCP.
Without multipath TCP, a TCP connection must be either on WiFi or on the mobile data connection, but not both. It is up to the OS to decide how allocate these connections. I think the standard Android decision is to use WiFi if available (and perhaps with sufficient signal strength) to minimize cost under metered data plans.
I'm not sure about your phone, but the Samsung Galaxy S5 can do that. It offers a "Download Booster" ability which connects to a Wifi and mobile data network simultaneously while downloading a file.
on android 6+ there is a developer option
for previous versions something like this should work, the methods numbers are android version specific and these should work for kitkat
#!/system/bin/sh radioM=20 mobileDataM=27 wlanIface=wlan0 ## turn on radio service call phone $radioM i32 1 ## turn on mobile data service call phone $mobiledataM ## set mobile data as preferred network service call connectivity $preferredNetworkM i32 0 ## wait for mobile data to connect while [ -z "$(ip a | grep ccmni | grep inet)" ]; do sleep 1; done ## reup wifi ifconfig $wlanIface up ## enable network bypassing android service echo enable_network 0 | wpa_cli -p /data/misc/wifi/sockets/ -i $wlanIface
The Speedify app seems to work for this purpose, and for free if you don't use a lot of data: http://speedify.com/
I happen to own a Kyocera Hydro Icon, and just tested it on 4.4.2, and it seems to enable to my phone to connect to and stream audio from my WiFi hotspot solely when configured as a microSD card server (meaning, it's not connected to the Internet), and to still access data over my phone's 4G/3G.