|Saturday, 21 October 2006|
In a typical computer system interconnected to a network, a network adapter, network card, or network interface adapter (NIA) acts as an interface between the host computer and a computer network. The network adapter performs the necessary interface functions for transmitting and receiving data over the computer network. A local area network (LAN) is a high bandwidth computer network, operating over an area, such as an office or a group of offices. In order for individual computers to communicate with others or with a host or server each computer must have a LAN adapter. The advent of laptop and palmtop personal computers with LAN interface adapters has enabled users to work with their personal computers while on business trips, and to communicate with their home office or with clients by plugging in to an available LAN cable connector. The LAN interface adapters conform to the Personal Computer Memory Card Industry Association (PCMCIA) standard 2.0. They contain communications circuits, processor circuits, and memory circuits to store the operating systems and protocols needed to perform the functions of a LAN interface adapter. A wireless LAN is typically implemented using radio transceivers which provide a wireless connection between the computing devices. Wireless access points are connected via a physical hardwire infrastructure to the computer network. Wireless access points further communicates via a radio link with radio transceivers associated with the computing devices of a user. Devices such as laptop or notebook computers, desktop computers, and even printers can be equipped with a wireless PC card, or wireless network adapter, containing the transceiver which communicates with the WAP.
Network devices generally use a combination of hardware and software to forward network traffic from one network interface to another. A network adapter may be coupled to a host system to provide communications. Some network adapters may provide hardware support for the processing of data related to the Transmission Control Protocol/Internet Protocol (TCP/IP) that may be used for communications. Such network adapters may be referred to as TCP/IP offload engine (TOE) adapters. Data networks are controlled by network protocols which according to the commonly used ISO model are classified into layers. The ISO layers include a physical layer, a data link layer, a network layer and so on. The physical layer defines all the electrical and physical specifications for devices. This includes the layout of pins, voltages, and cable specifications. Hubs, repeaters, network adapters and host bus adapters are physical-layer devices. The physical layers are typically implemented on network adapter cards with efficient integrated circuits. Higher layers are handled by software drivers for the adapter cards and by a protocol stack executed in the host processor. Network adapters involved in the transfer of data between a communications network and a host computer system typically must notify the host system of asynchronous events. For example, if the network adapter has begun receiving a data frame, the host processor may want to know when a complete data frame has been received. In a network, computers may be accessed and controlled remotely by other computers using a hardware network adapter installed in the computer. This network adapter is connected directly to the other computers or attached to a LAN. These devices typically require network adapter software to be installed to permit a device to access or control the computer.
The LAN adapter functions as an interface between the computer and the network cabling. The network interface card moves data to and from random access memory inside the computer and also controls the flow of data in and out of the network cabling system. The network interface card has a specialized port that matches the electrical signaling standards used on the cable and the specific type of cable connector. The network adapter includes a memory for storing data or software program code images that the host computer utilizes in communicating over the computer network. The data and software program code images must be accessible to the host computer in order to be accessed and utilized by the host computer. In a network adapter, a shared memory subsystem is connected to a network controller chip by a shared system bus. The network controller located in a network adapter manages transmission and reception of data packets by transferring data between the network and a shared memory subsystem. The shared memory is used by several different devices including the system CPU, I/O devices and disks as well as the network. The network adapter accesses the shared memory by a shared system bus. Most network adapters use a store and forward adapter memory to send and receive messages to and from the network. Normally a single memory at the adapter supports four ports to handle the message traffic to and from the network. Two styles of LAN adapter have emerged due to the predominance of Ethernet and Token-Ring networks. The Ethernet MAC protocol requires no local processing, so Ethernet adapters tend to be simple "dumb" adapters. The Token-Ring protocol requires local processing of MAC frames by the adapter, hence Token-Ring adapters need a local CPU, making them "smart" adapters.