Installation guide

Network Infrastructure for EtherNet/IP™
Designing the Infrastructure
4-44
appropriate segment. Since any segment contains only a single node, the frame only reaches the intended
recipient. Before switches were used, Ethernet was a half-duplex network. Thanks to managed and
unmanaged switches, Ethernet can be a full-duplex network.
Switched Networks and Full-Duplex Ethernet
In a switched network, nodes only communicate with the switch and never directly with each other.
With a dedicated segment for every node, switching allows a network to maintain full-duplex
Ethernet.
Switched networks employ either twisted-pair or fiber-optic cabling, both of which use separate
conductors for sending and receiving data. In this environment, Ethernet nodes can forgo the collision
detection process and transmit at will, since they are the only potential devices that can access the
medium.
In other words, traffic flowing in each direction has a lane to itself. This allows nodes to transmit to the
switch at the same time the switch transmits to them, achieving a collision-free environment. Transmitting
in both directions also can effectively double the apparent bandwidth of the network when two nodes are
exchanging information. For example, if the speed of the network is 100 Mbps, then each node can
transmit at 100 Mbps at the same time.
4.7 Switching Technologies
Switches usually work at Layer 2 (data link) of the OSI Reference Model using MAC addresses while
routers work at Layer 3 (network) with Layer 3 addresses (IP, IPX®, or AppleTalk® depending on what
Layer 3 protocols are being used). The algorithm that switches use to decide how to forward packets is
different from the algorithms that routers use to forward packets.
One of the differences between the algorithms of switches and routers is how each algorithm handles
broadcasts. On any network, the concept of a
broadcast packet is vital to the operability of the network.
Whenever a device needs to send out information but does not know where to send it, it sends out a
broadcast. For example, every time a new computer or other device comes onto the network, it sends out
a broadcast packet to announce its presence. Broadcasts are transmitted any time a device needs to make
an announcement to the rest of the network or is not sure where to send information.
A switch will pass along any broadcast packets it receives to all other segments in the broadcast domain,
but a router will not. Without the specific address of another device for which a message is intended, a
router will not let the data packet pass through. This is an effective way of keeping networks separate
from each other but is not helpful when different parts of the same network need to communicate with
one another. Switches provide a solution to this problem.