Envoy ACP/XF Application Programming Manual

Asynchronous Balanced Mode (ABM) Protocols

EnvoyACP/XF Application Programming Manual–132179

2-3

ABM Link-Level Responses

EnvoyACP/XF automatically transmits the following link-level responses from the local

station to the remote station (these responses are transparent to the application program):

ABM Inactive States

There are two inactive states for the ABM protocols (Figure 2-2). The type of inactive

state determines how a station responds to a SABM command from the other station on

the link.

•

Disconnected. The station is in Logical Disconnect State (LDS). The station

responds with a DM to a SABM or SABME received from the remote station,

preventing the link from being activated.

•

Offline. The communications line is in Logical Disconnect State (LDS) but is

inactive. In this state, the station responds with a UA to the SABM or SABME

received from the remote station, then goes online, allowing the link to be activated.

RR Receive Ready (I-frame acknowledgment; ready to accept more data)

RNR Receive Not Ready (I-frame acknowledgment; no more I-frames can be

accepted)

REJ Reject (I-frame acknowledgment; out-of-sequence I-frame received)

SREJ Selective Reject (I-frame acknowledgment; requests retransmission of a

specific I-frame without retransmission of subsequent I-frames)

DM Disconnect Mode

UA Unnumbered Acknowledgment (response to SABM, SABME, DISC, or

RSET command)

FRMR Frame Reject (invalid frame format, invalid command, or invalid response

received)