Technical data

www.westermo.com Theoretical and general applications 113

… Assume that A intends to send a packet to B.

… The network includes a certain amount of equipment that has an internal

delay (t).

… A continuously empties its send buffer, when no collision is discovered.

… A collision occurs on the outermost node on the network (E).

… All data (D) is not received, which results in (B) not being able to interpret it.

… The collision signal (F) is sent back to the transmitter (A).

… When the domain is too large, the collision signal does not reach (A) before the

send buffer has been emptied. This makes it impossible to retransmit the packet.

IP Networks

Internet Protocol

IP or Internet Protocol is designed for connections in a network or between several

networks. When the specification was written it was understood that new technolo-

gies and new transfer methods would be continuously developed. This is why an open

standard that is primarily independent of the underlying network and medium was

developed. TCP/IP is a family of protocols that extends between many different layers

in the OSI-model.

Addressing methods

Much of the information in a network goes from single sender to a single receiver. This

is completely natural in most cases, for example, a PLC communicating with an I/O

device. This kind of transfer is usually called unicast.

The opposite to unicast is “broadcast”, i.e. the way that radio and television are trans-

mitted: one sender and many receivers. Broadcasting means that information is sent

out to everyone, the technique is used in some closed computer networks, but broad-

casting over the entire Internet is impossible as it would overload the network.

Multicast is a technique that fits in between unicast and broadcast. Information is not

sent out indiscriminately to everyone as in broadcasting, but the same information can

have numerous receivers unlike unicasting. Using multicast allows the building of distri-

bution networks, which are suitable for video monitoring or television transmissions

over the Internet, i.e. information with one sender and many receivers. Multicast will

open up new possibilities for the Internet and prevent it from collapsing due to over-

Network

Unicast

Broadcast

Multicast

B A C K