An Open C Layer is a cohesive piece of software that provides a well defined service and has a set of well defined interfaces. An OSI Open C Layer implements an OSI protocol. Open C Layers have a consistent design architecture. Each implementation of an OSI protocol, provides to its user the set of services defined for that protocol at its upper interface. It assumes the services of the layer below it to be present at its lower interface.
A typical software layer (N) appears to its user as a link module with four defined interfaces. The figure below (Figure 2.1) presents an interface model for the (N) software module.
The (N) Open C Layer is expected to provide the services defined for the (N) layer at its upper interface. The (N) Open C Layer's upper interface is a series of function calls (primitives). Each function call accepts a group of arguments (parameters). Each function call is non-blocking.
(N) request and responses, collectively referred to as (N) action primitives, are function calls into the (N) Open C Layer. (N) action primitives are invoked by the (N) service user. The code for (N) action primitives is inside the (N) Open C Layer.
(N) indication and confirmations, collectively referred to as (N) event primitives, are function calls outside of the (N) software module. (N) event primitives are invoked by the (N) software module. The code for (N) event primitives is expected to be provided by the (N) service user. The entry point for (N) event primitives is conveyed to the (N) layer during the creation of the service access point by (N) service user.
The (N) Open C Layer may use the services defined for the (N-1) layer at its lower interface. The lower interface of the (N) software module matches the upper interface of (N-1) software module.
Operation of an OSI layer may be monitored and manipulated by the Network Management Administrator. To provide for this each Open C Layer is responsible for providing an interface that allows for network management administration.
Within each Open C Layer, often a Layer Management Entity (LME) is responsible for defining and providing the network administration interface.
An Open C Layer can rely on the services provided by the Open C Platform. The interface and the description of the services provided by the Open C Platform is described in this book.
The following is a list of significant events that result into execution of code inside of (N) Open C layer.
