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Network Software - Coggle Diagram
Network Software
Protocol Hierarchies
To reduce their design complexity, most networks are organized as a stack of layers or levels, each one built upon the one below it. The number of layers, the name of each layer, the contents of each layer, and the function of each layer differ from network to network.
The purpose of each layer is to offer certain services to the higher layers while shielding those layers from the details of how offered services are actually implemented.
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Service Primitives
A service is formally specified by a set of primitives (operations) available to user processes to access the service. These primitives tell the service to perform some action or report on an action taken by a peer entity. If the protocol stack is located in the operating system, as it often is, the primitives are normally system calls.
These calls cause a trap to kernel mode, which then turns control of the machine over to the operating system to send the necessary packets.
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Services to Protocols
Service is a set of primitives (operations) that a layer provides to the layer above it. The service defines what operations the layer is prepared to perform on behalf of its users, but it says nothing at all about how these operations are implemented.
Protocol is a set of rules governing the format and meaning of the packets, or messages that are exchanged by the peer entities within a layer. Entities use protocols to implement their service definitions. They are free to change their protocols at will, provided they do not change the service visible to their users.