| In this chapter, we study the internal structure of the network subsystem provided in FreeBSD. The networking facilities provide a framework within which many network architectures may coexist. A network architecture comprises a set of network-communication protocols, the protocol family; conventions for naming communication endpoints, the address family; and any additional facilities that may fall outside the realm of connection management and data transfer. Networking facilities are accessed through the socket abstraction described in Chapter 11. The network subsystem provides a general-purpose framework within which network services are implemented. These facilities include the following: A structured interface to the socket level that allows the development of network-independent application software A consistent interface to the hardware devices used to transmit and receive data Network-independent support for message routing Memory management
We describe the internal structure of the network subsystem in Section 12.1. Then we discuss the interface between the socket layer and the network facilities and examine the interfaces between the layers of software that make up the network subsystem. In Section 12.5, we discuss the routing services used by the network protocols; in Section 12.6, we describe the mechanisms provided to manage buffering and to control congestion. We present the raw-socket interface that provides direct access to lower-level network protocols in Section 12.7. Finally, in Section 12.8, we discuss an assortment of issues and facilities, including out-of-band data, subnetwork addressing, and the address resolution protocol. After we have discussed the framework in which the network protocols fit, we shall examine the implementations of several existing network protocols in Chapter 13. A detailed description of the internal data structures and functions of the network layers and protocols can be found in Wright & Stevens [1995]. |
