Communication Networks/Network Basics

What are networks?
Networks are large distributed systems designed to send information from one location to another. An end point is a place in a network where data transmission either originates or terminates. A node is a point in the network where data travels through without stopping. Nodes are connected by channels, paths that data flows down. Channels can be physical linear objects such as a wire or a fiber optic cable, or it can be less tangible, like a wireless connection at a particular frequency.

Providers and consumers
An end point that produces information is known as a producer or a server. An endpoint that receives information is known as a consumer or a client. In many networks, such as bi-directional networks, an endpoint can be both a client and a server.

Bi-directional communications
Bi-directional communications means that data is flowing both to and from an end point. An end point can be both a client and a server.

Point-to-point communication
Some channels are point-to-point: they have only a single producer (at one end), and a single consumer (at the far end).

Many networks have "full duplex" communication between nodes, meaning they have 2 separate point-to-point channels (one in each direction) between the nodes (on separate wires or allocated to separate frequencies).

Some "mesh" networks are built from point-to-point channels. Since wiring every node to every other node is prohibitively expensive, when one node needs to communicate with a distant node, the "intermediate" nodes must pass through the information.

Multiple access
Multiple access networks are networks where multiple clients, multiple servers, or both are attempting to access the network simultaneously. Networks with one server and multiple clients are called "broadcast networks", "multicast networks", or "SIMO networks". "SIMO" stands for "Single Input Multiple Output". Networks with multiple clients and servers are known as "MIMO" or "Multiple Input Multiple Output" networks.

Data collisions
In a MIMO network, when multiple servers attempt to send data on a single channel at the same time, a data collision occurs. Because data typically consists of electric or electromagnetic radiation, a data collision causes both pieces of information to become unreadable. Clients on the network will either read meaningless data (garbage data) or will read no data at all. MIMO networks therefore will use some sort of collision avoidance or collision detection mechanisms to prevent data collision problems from affecting the network.

Networks with only one fixed sender per channel (point-to-point channels and SIMO channels) never have data collisions on the channel.