For a connection to a host computer using a leased SDLC line, the SNALink receives an SNRM when the end-to-end connection is established. The SNALink responds with a UA and informs the local node that the connection is ready for data transfer. This is done with the Request-Open-Station message with the Rcv-Set-Mode flag set.
The node then opens the STATION LPI connection with the Open(STATION) message. If the SNALink has an available control block, it responds with an Open(STATION) OK Response. This is followed by a Station-Contacted message.
A channel connection is treated the same way as a leased secondary SDLC connection. Each channel connection is associated with a channel subaddress in the range 0x00 to 0xFF. The SNA Server node will send the channel link service an Open(LINK) Request for each configured channel connection when the connection is activated. The link service should expect to receive multiple Open(LINK) Requests, one for each supported subchannel address.
Note that the Request-Open-Station message flows on the LINK LPI connection, whereas the Station-Contacted message flows on the STATION LPI connection.
The message flow for a leased line is shown in the following figure.