The token-ring data link control (DLCTOKEN) supports the logical link control (LLC) protocol and state tables described in the Token-Ring Network Architecture Reference, which also contains the local area network (LAN) IEEE 802.2 LCC standard. Both address-resolve services and name-discovery services are supported for establishing remote connections. DLCTOKEN supports a direct network interface to allow a user to transmit and receive unnumbered information packets directly through DLCTOKEN without the data link layer performing any protocol handling.
A combined station is supported for a balanced (peer-to-peer) configuration on a logical point-to-point connection. That allows either station to initiate asynchronously the transmission of commands at any response opportunity. The sender in each combined station controls the receiver in the other station. Data transmissions then flow as primary commands, and acknowledgments and status flow as secondary responses.
Both asynchronous disconnect mode (ADM) and asynchronous balanced mode extended (ABME) are supported. ADM is entered by default whenever a link session is initiated, and is switched to ABME only after the set asynchronous balanced mode extended (SABME) command sequence is complete. Once operating in ABME, information frames containing user data can be transferred. ABME then remains active until the LLC session terminates, which occurs because of a disconnect (DISC) command packet sequence or a major link error.
All communication between a local and remote station is accomplished by the transmission of a packet that contains token-ring headers and trailers as well as an encapsulated LLC Link Protocol Data Unit (LPDU). The DLCTOKEN Frame Encapsulation figure illustrates the token-ring data packet.
The token-ring data packet consists of the following fields:
|AC||Access control field|
|FC||Frame control field|
|LPDU||LLC Link Protocol Data Unit|
|DSAP||Destination service access point (SAP) address field|
|SSAP||Source SAP address field|
|CRC||Cyclic redundancy check or frame-check sequence|
|FS||Frame status field|
|m bytes||Integer value greater than or equal to 0 and less than or equal to 18|
|n bytes||Integer value greater than or equal to 3 and less than or equal to 4064|
|p bytes||Integer value greater than or equal to 0 and less than or equal to 4060|
Note: SD, CRC, ED, and FS headers are added and deleted by the hardware adapter.