Microsoft KB Archive/103952
Article ID: 103952
Article Last Modified on 2/26/2002
This article was previously published under Q103952
LOCAL AREA NETWORK
A local area network (LAN) provides peer-to-peer communication among independent devices located within a moderately sized geographical area.
The computer devices attached to the local area network and intended for running application programs are called stations, hosts, or end systems. Examples are LAN Manager workstations and servers.
The cable system used to carry data from station to station is called the physical medium. Examples are twisted wire pair, coaxial, and fiber optic cable.
Intermediate systems equipment passes information between physical medium segments. Examples include repeaters, bridges, routers and brouters.
A network connected byte-level information processor. Stations, bridges, routers and brouters are nodes, but repeaters are not.
Functions are specific network tasks such as:
- Remote file access
- Password encryption and decryption
- Inter-process session establishment
- Message segmentation and de-segmentation
- Frame routing to off-segment networks
- Frame delimiting and media access arbitration
- Pulse encoding of bits
To reduce network design complexity, functions are organized into groups, which are then allocated to a series of layers implemented in software that runs on the network nodes.
The purpose of each network layer is to offer specific services to the higher layers and to shield them from the details of how services are implemented. The services provided by a given layer are a product of the network functions allocated to and performed by that layer.
The rules and conventions that allow layer N on one node to carry on a conversation with layer N on another node are collectively known as the layer N protocol.
Except at the lowest level (the physical medium) no data moves directly from layer N on one node to layer N on another node. Instead, each layer passes data to the layer below it, until the physical medium is reached. The data is then transmitted to the destination node and back up through each higher layer to layer N. Control information attached to the data is used to navigate the path through the layers.
Between each pair of adjacent layers there is a well defined interface that defines which services the lower layer offers to the upper one, and how those services are accessed.
For example, peer processes in layer 4 communicate "horizontally" using the layer 4 protocol. Each side is likely to have the procedures SendToOtherSide and GetFromOtherSide, even though these procedures actually communicate with lower layers across the 3 - 4 interface, not directly with the other side.
A network's complete set of layers, allocated functions, peer protocols, and vertical interfaces constitutes its architecture.
Keywords: kbinfo KB103952