The Synchronous Connection Oriented link is one of the two possible Bluetooth data link types defined. The SCO link is a symmetric, point-to-point link between the master device and a specific slave device. The SCO link reserves slots between the master and the slave and can therefore be considered to provide a circuit switched connection. The SCO link is usually used to support time critical information, e.g. voice, since time critical SCO packets are never retransmitted. The master device can support up to three SCO links, this might be to the same slave or to different slaves. A slave can support up to a maximum of three SCO links, assuming they are from the same master. If the slave has links from different masters, a maximum of two SCO links are available.