In IEEE 1394, 80% of the bus is reserved for isochronous cycles, leaving asynchronous data with a minimum of 20% of the bus. FireWire uses Data/Strobe encoding (D/S encoding). In D/S encoding, two non-return-to-zero (NRZ) signals are used to transmit the data with high reliability. The NRZ signal sent is fed with the clock signal through an XOR gate, creating a strobe signal. This strobe is then put through another XOR gate along with the data signal to reconstruct the clock. This in turn acts as the bus's phase-locked loop for synchronization purposes. The process of the bus deciding which node gets to transmit data at what time is known as arbitration. Each arbitration round lasts about 125 microseconds. During the round, the root node (device nearest the processor) sends a cycle start packet. All nodes requiring data transfer respond, with the closest node winning. After the node is finished, the remaining nodes take turns in order. This repeats until all the devices have used their portion of the 125 microseconds, with isochronous transfers having priority. The previous standards and its three published amendments are now incorporated into a superseding standard, IEEE 1394-2008. The features individually added give a good history on the development path. The original release of IEEE 1394-1995 specified what is now known as FireWire 400. It can transfer data between devices at 100, 200, or 400 Mbit/s half-duplex data rates (the actual transfer rates are 98.304, 196.608, and 393.216 Mbit/s, i.e., 12.288, 24.576 and 49.152 MB/s respectively). These different transfer modes are commonly referred to as S100, S200, and S400. Cable length is limited to , although up to 16 cables can be daisy chained using active repeaters; external hubs or internal hubs are often present in FireWire equipment. The S400 standard limits any configuration's maximum cable length to . The 6-conductor connector is commonly found on desktop computers and can supply the connected device with power. The 6-conductor powered connector, now referred to as an alpha connector, adds power output to support external devices. Typically a device can pull about 7 to 8 watts from the port; however, the voltage varies significantly from different devices. Voltage is specified as unregulated and should nominally be about 25 volts (range 24 to 30).