User Guide User guide

VN-MATRIX User Guide Appendix C: Browser Configuration
Page 130 I458GB issue 6
Nodes, Switchers & Routers
An Ethernet Local Area Network (LAN) will have a number of nodes, and in principle all nodes can
communicate with each other. The principle used is “Carrier Sense, Multiple Access/Collision
Detection” or CSMA/CD. This means that when not transmitting, all nodes are listening. When a node
transmits no other node attempts transmission. However, signal speed limits mean that a “collision” is
possible. Such collisions are detected and the competing parties “back off” for another attempt. The
principle works well for small networks, but introduces inefficiency in networks with high traffic.
Networks are in practice, therefore, constrained by the use of various switching and routing devices.
 An Ethernet hub simply allows nodes to be connected together and CSMA/CD applies.
 An Ethernet switch intelligently routes internode traffic; i.e. nodes only receive traffic
addressed to them. This reduces or eliminates bus contention at the local level. A switch can
also allow a node to operate duplex communication i.e. simultaneous transmit and receive.
 An Ethernet bridge is a two port switch used for segmenting networks or joining dissimilar
media.
 An Ethernet router connects multiple networks, and connects to networks of other types.
Routers and switches use routing tables to determine how traffic is directed. These can be dynamic,
in the sense that they are generated as needed by examining the traffic; but they can also be static,
imposing strict rules about how traffic is directed.
This factor is of great importance in respect of transmitting image data over networks. In practice
unless a network is specifically programmed to carry image data, it is likely that the data will be
blocked at the first router it encounters.