|IEEE 802.4 Token Bus|
|Type:||Physical and data link layer protocols.|
The Data Link Layer is divided into two sublayers:
IEEE 802.2 LLC fields are optional. But to transfer IP packets over IEEE 802 networks, the IEEE LLC and SNAP fields are utilized.
IP datagrams are sent on IEEE 802 networks encapsulated within the 802.2 LLC and SNAP data link layers, and the 802.3, 802.4, or 802.5 physical networks layers. The SNAP is used with an Organization Code indicating that the following 16 bits specify the EtherType code.
In IEEE 802.4, the token passing scheme is used in place of Carrier Sense Multiple Access with Collision Detection (CSMA/CD) on a bus local area network (LAN). A token is circulated on a network. The computer that has possession of the token has the right to transmit packets for a certain period of time. If that computer has no packets to transmit then the token is passed to the next computer. Only one computer at a time can transmit packets so this helps to avoid collision problems.
[RFC 1042] A Standard for the Transmission of IP Datagrams over IEEE 802 Networks.
[RFC 1230] IEEE 802.4 Token Bus MIB.
[RFC 1239] Reassignment of Experimental MIBs to Standard MIBs.
[RFC 948] TWO METHODS FOR THE TRANSMISSION OF IP DATAGRAMS OVER IEEE 802.3 NETWORKS.