Standard Ethernet data link
control (DLCETHER) is initialized at the open link station as a combined
station in asynchronous disconnect mode (ADM). As a secondary or
combined station, DLCETHER is in a receive state waiting for a command frame
from the primary or combined station. The following command frames are
accepted by the secondary or combined station at this time:
|SABME||Set asynchronous balanced mode extended|
|XID||Exchange station identification|
|UI||Unnumbered information - datagram|
Any other command frame is
ignored. Once a SABME command frame is received, the station is ready
for normal data transfer, and the following frames are also accepted:
|RNR||Receive not ready|
As a primary or combined station, DLCETHER can perform ADM XID, ADM TEST exchanges, send datagrams, or connect the remote into the asynchronous balanced mode extended (ABME) command frame. XID exchanges allow the primary or combined station to send out its station-specific identification to the secondary or combined station and obtain a response. Once an XID response is received, any attached information field is passed to the user for further action.
The TEST exchanges allow the primary or combined station to send out a buffer of information that is echoed by the secondary or combined station to test the integrity of the link.
Initiation of the normal data exchange mode, ABME, causes the primary or combined station to send a SABME command frame to the secondary or combined station. Once sent successfully, the connection is said to be contacted, and the user is notified. I-frames can now be sent and received between the linked stations.