Figure 1-7 shows how STREAMS can move functions between kernel software and front-end firmware. A common downstream service interface lets the transport protocol module be independent of the number or type of modules below it. The same transport module will connect without modification to either an X.25 module or X.25 driver that has the same service interface.
By shifting functions between software and firmware, you can produce cost-effective, functionally equivalent systems over a wide range of configurations. This means you can swiftly incorporate technological advances. The same transport protocol module can be used on a lower-capacity machine, where economics preclude the use of front-end hardware, and also on a larger scale system where a front-end is economically justified.