ICP DAS USA TDRS4050601 - Manual (Page 13)

Industrial Redundant Ring Switch – RS Series User Manual
TDRS4050601 5
Ethernet Switch
Ethernet is an ideal medium to transport large volumes of data, at speed, across great
distances. Previously, multiple networks carrying specific protocols were installed side by
side to carry out unique tasks. This inevitably led to project costs increasing as additional
fiber optic or copper cables were installed to deal with the increasing volume of data.
Using Ethernet a single fiber optic cable can carry multiple protocols. Furthermore,
manufacturers are exporting their legacy protocols onto Ethernet, designing new IP
based communication protocols and providing embedded Web-Pages within devices that
offer real-time information using simple tools like Internet Explorer and Netscape
Navigator.
Unfortunately, although network hardware has dramatically increased in speed and
technology over the past decade the poor perception of Ethernet has remained; namely
as being difficult to fault-find and critically being a non-deterministic network. A key
development that overcame some of these issues was the advent of the Ethernet Switch.
Early Ethernet networks were based on a hub or repeater. These units have no
intelligence and therefore are unable to identify any information contained within the
Header frame of an Ethernet packet. This means that it is not capable of determining
which port to send the frame to. Therefore, every frame is sent to every port. A network of
repeaters and hubs is called a „Shared Ethernet‟ or „Collision Domain‟. Various devices
will all compete with each other before sending data using „Carrier Sense Multiple Access
/ Collision Detect‟ (CSMA/CD) protocol. This means that only one system is allowed to
proceed with a transmission of a frame within a Collision Domain at any one time. This is
a major disadvantage when using Hubs and Repeaters within a network.
A switch, like a hub, has to forward and receive packets from one network or device to
another. The switch could forward all packets, but if this was the case it would have
similar behaviour to a hub. It would be more intelligent if the switch only forwarded
packets which needed to travel from one network or device to another. To do this, the
switch must learn which devices or networks are connected to each port. In simplistic
terms; it needs to learn the destination and source ports of each and every packet
received on each individual Switch port. Once learnt, any identically addressed packet
will be automatically be forwarded. With today‟s enhanced processing power the
introduction of a Switch has significantly increase network bandwidth.
Industrial Ethernet
Industrial rated Switches are intended to be installed in both harsh climatic environments
and noisy electrical installations. Such Switches are an excellent example of true
industrial design principles –
 very high operating temperatures (down to -30°C and up to 75°C)
 dual input power supplies
 wide DC operating voltages
In Roadside and tunnel applications distances between cabinets with a suitable power
supply can be challenging. Naturally, fiber optic cable is the preferred solution. Using
single mode fiber, runs of up to 85km are possible. Even using standard CAT5e copper
cable the Industrial Switch supports the long cable specification and distances of up to
185m are viable. However, the domain of Ethernet has always been controlled by the IT
department who normally configured office networks with an iron fist and dictated to the
organisation how the network would be designed. Complex network recovery protocols