How HP OTS/9000 Establishes a Connection

Establishing a connection between local and remote systems involves the following:

Higher-layer applications, such as FTAM and X.400, require address information and NSAP values. The addresses determine the peer entity at each layer of the stack. See "Addressing" in the "Resources" chapter of this manual.
A user-created application uses the stream /dev/osipi or /dev/ositpi for primitive requests. The application registers with OTS using its local address.
Upon successful registration, the application sends a connect request to the remote system.
- If the remote is connected through CONS, OTS/9000 looks up its X.121 address in the OTS configuration and sends a call packet.
- If the system is attached to an 802.3 or FDDI LAN, OTS/9000 uses the ES-IS protocol to determine the Media Access Control (MAC) address for the destination NSAP.
After the remote address is determined, OTS/9000 normally issues the connect request to establish a connection if the type of network service used is a Connection-Oriented Network Service (CONS). This is provided on X.25 networks.
If another network service type, Connectionless Network Service (CLNS), is used, it differs only in that there are no network layer connections established. OTS/9000 provides CLNS over FDDI, IEEE 802.3 LANs and X.25.

Technical documentation