How do you create a ring network

Token Ring - IEEE 802.5

To avoid chaos, the token passing procedure is used. This method ensures that not all participants send into the network at the same time. Only computers that are currently in possession of the token have the right to send data packets into the network. This token is passed on in a ring - even if no participant needs a transmission permit, the token continues to circulate. A token is an empty frame with a size of 3 bytes, where each byte has 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 occupied.
  • First byte - End Delimiter (ED): The structure of the end delimiter is similar to the start delimiter and makes it clear that the frame is terminated.

If a participant receives the frame and doesn't want to send any information, they simply pass it on to the next in line. However, if the computer wants to send something, it changes the token bit and appends the actual data packet to the token. Now he sends the package off. Part of this frame is now also the sender and recipient address. Nevertheless, the data packet does not immediately reach the recipient, but is passed on from participant to participant via the MAU until it has reached the correct station. So that the signal does not lose strength en route, each participant acts as a repeater: It reads in the packet, creates it again and sends it back into the ring.

The destination station copies the information, confirms correct receipt of the data by changing the Frame Status (FS), the last byte in the entire frame, and forwards the packet. When the data packet has reached the original sender again, it deletes the data and releases the token bit again. Alternatively, he now also has the option of sending the next data straight away. A token holding time has been implemented so that all participants have the chance to transmit data. This time indicates how long a station can use the token for itself.