Connecting via multicast:

Make sure your device is logged into the same network that the computer you want to control is part of.

In the app go to Setup / MIDI Ports, set the desired port to WiFi / Multicast and click OK.

The final instructions dialog contains an option to run both in- and output over the same port. This is mainly for the built-in ipMIDI support in Mixbus and Ardour. For other use-cases it may be smarter to stick with the defaults and use seperate ports, ie. have only one data source per multicast group.

Multicast with ipMIDI

Download and install ipMIDI for Windows and OS X, resp. multimidicast or qmidinet for Linux.
(ipMIDI for Windows costs serious money, but it may be worth it. A free demo is available.)

Once done, launch the ipMIDI control panel (accessible via a quicklaunch icon in Windows Taskbar or the ipMIDI icon in the MIDI window of OS X's Audio MIDI Setup) and raise the number of ports to 4 or more. A reboot may be required after this.

You are then ready to exchange MIDI via multicast, but still need to select ports in your sequencer. See sequencer settings

Multicast with mnet / MIDIHub

mnet is preconfigured with 2 bidirectional multicast connections. These however are initially hidden. Click the greyed out multicast icon on the top left to have them shown. Drag patchlines to the MIDI ports you want to recive MIDI on and you should be good to go.

General notes:
Multicast connections do not require any session creation and the connection process itself is much simpler than it is with RTP - there is no handshaking and quality negotiation going on between host and client etc. This makes using multicast the easiest to use connection method in TouchDAW. It has another big advantage in that the session can be left and rejoined by any party at any time without the need to reestablish anything when getting back in. In principle though, this is related to the fact that neither party has any real idea of the other with multicast. Both sides will just send what they have to send and immediately forget about it without giving or expecting any sort of feedback. As DAW control related communication should not involve anybody else than the DAW and one controller per MIDI connection, multicast may conceptually not be ideal for the task, because other clients can connect to the same multicast group and interfere with the control flow at any time. That said, multicast connections are still perfectly useable for DAW control when taking a little care and they may even be preferable because of he easy join / leave procedure.

Important: Some Android handsets are crippled by manufacturers for the sake of longer battery life and will not allow you to receive multicast data. This is a known issue with a number of HTC devices (some Sony and Samsung ones being severly bandwidth limited) and makes TouchDAW's multicast mode unuseable for DAW control on the device!