Additionally, each layer consists of two parts: a service definition, which defines the type
of service a layer provides, and a protocol specification that details the rules governing the
implementation of a particular service. Lower layers provide services to upper layers.
42. What kinds of services do layers provide to each other?
There are two different types of services: connection-oriented and connectionless.
Some layers have an additional type of service called multiplexing, but this does not neces-
sarily transcend all layers of the architecture. Services are available at service access
points (SAPs), with ...
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