Voltage Switches

Voltage switches use a DC voltage to switch to the alternate input. The control voltage may be supplied by a dedicated jack on the switch, or derived from the IRD coax connection. Many BUD and some Dish Network IRDs provide a dedicated jack for switch control. Some common control voltages for primary/secondary are 0/6, 0/12, and 14/18. A relay is typically used for signal switching. An example of a voltage switch is the Dish Network model SWAJ (discontinued).

A 22 kHz tone generator can be connected to the switch control jack of an IRD to allow the use of a 22 kHz switch rather than a voltage switch. This scheme was used by Dish Network to control the model SW44 switch (discontinued).
22 kHz Switches

22 kHz switches use a continuous 22 kHz 600 mV peak-to-peak signal to switch to the secondary input. This type if switch is used by DirecTV
DiSEqC - Digital Satellite Equipment Control

The DiSEqC protocol is used by switches and other satellite equipment, such as dish positioners. A serial protocol is sent on a keyed 22 kHz carrier. The on/off times of the carrier signal encode the logic level. DiSEqC supports unidirectional and bidirectional communication. The DiSEqC protocol supports identification and cascadeing. This type of switch is used by DVB receivers. Technical information about DiSEqC can be found here.
Dish Network Switches

The old lineup of Dish Network multi-dish switches - SW21, SW42, and SW64 - use a low bit rate (125 bps) serial protocol to control switching. The LNB control voltage is used to encode the logic level. Communication is unidirectional, from IRD to switch. The use of a serial protocol allows switches to be addressable. Each type of switch can be given a unique address that only it will respond to. The switch type can be identified and un-like switches (with different addresses) may be cascaded. The IRD must be aware of the possible types and arrangements of switches that could be connected - this requires a firmware update when new switch models are released. The IRD can identify what switches are present by sending a command to any possible switch address and detecting if the signal from the LNB changes. A change in signal indicates that a switch of the addressed type is present.