To avoid chaos, the token passing procedure is used. This method ensures that not all participants send data to the network at the same time. Only computers that are currently in possession of the token have the right to send data packets to the network. This token is passed on in a ring – even if no participant requires a transmission permit, the token continues to circulate. A token is an empty frame of 3 bytes in size, each byte having a separate task:
- Third byte – start delimiter (SD): The first 8 bits of the frame indicate the beginning of the token. The structure is based on the differential Manchester code, which allows a clear assignment.
- Second byte – access control (AC): The access control contains the token bit. If this is set to 0, the token is free, 1 indicates that it is busy.
- First byte – end delimiter (ED): The design of the end delimiter is similar to the start delimiter and makes it clear that the frame is complete.
If a participant receives the frame and does not want to send any information, they simply pass it on to the next in the row. However, if the computer wants to send something, it changes the token bit and attaches the data package to the token. Part of this frame is now also the sender and recipient address. However, the data packet does not immediately reach the receiver, but – via the MAU – is forwarded from participant A to participant B, to C, and so on, for example, until it reaches the correct station. To ensure that the signal does not lose strength on the move, each participant acts as a replicator: it reads in the packet, regenerates it, and sends it back into the ring.
The target station then copies the information, receives the data, and acknowledges this by changing the frame status (FS), the last byte in the whole frame, and transmits the packet. When the data package reaches its original sender again, it deletes the data and releases the token bit again. A token holding time is implemented so that all participants have the chance to transmit data. This time specifies how long a station may take the token for itself.