6100 ADCCP Programming Manual

Protocol Task Architecture
ADCCP Link and Station Management
069225 Tandem Computers Incorporated 2–3
A request does not need to pass through all levels of the software shown in Figure 2-1.
The Protocol Manager decodes each request and routes it to the appropriate level. In
general, the following cases would not require the use of every level of the software:
The request does not entail action on the line (for example, the request simply
changes or retrieves configuration data). In this case, the Protocol Manager
handles the request without involving lower levels of software.
The request entails an action on the line but does not address a specific station. In
this case, the Level 1 Protocol handles the request, using the driver routine.
Modem-control requests fall into this category.
The request entails communication with a specific station. In this case, the Level 2
Protocol handles the request. Level 1 takes output frames from Level 2 and uses
the driver routine to place the frames on the line.
Not all protocol actions are triggered by application requests. A frame arriving on the
line might satisfy a request, but it can also be a command or response from a remote
station. When a frame arrives, the driver receives it. The Level 1 Protocol checks the
address to identify the remote station and passes the frame to the Level 2 Protocol.
Level 2 sends any required response to the remote station, passing its output frame to
Level 1 for transmission. If the arriving frame is intended for the application (for
example, if it is an I-frame), Level 2 informs the Protocol Manager, which responds to
the application. Figure 2-2 presents a simplified view of the ADCCP protocol module
handling input frames. Frame handling is described further in, “Polling,” later in this
section.