GE 1601-9026-A3 Switch User Manual

7 Hubs and Switches
Two of the major Ethernet LAN components are "hubs" and "switches." There are many
advantages of a switch over a hub. Hubs just transfer information from one port to all
other ports. Since a hub has no way of handling media contention, collisions can occur
requiring all segments connected to a hub to work in a half duplex mode. Switches on the
other hand have the capability of buffering messages allowing full duplex operation. A
switch will also learn the MAC addresses of devices connected to each of it’s ports and will
then route messages to just the port to which the destination device is connected, thereby
reducing data traffic on the network. Switches that have configuration firmware to
customize the switch and traffic are called “managed switches”. Switches that have fixed
configurations are referred to as “unmanaged switches”.
7.1 Fiber Optic Ethernet:
Fiber optic Ethernet is rapidly becoming the medium of choice in applications where longer
distances and immunity to EMI are of importance, such as power system applications.
However, the higher cost and the difficulty of terminating fiber cables allows twisted pair
to continue to play a roll were appropriate.
The wavelengths of light used in fiber optic communication are 820, 1300 and 1550
nanometers (nm) because it has been found that these wavelengths of light are
attenuated the least as they travel through the fiber optic medium. Compatible ports must
operate at the same wavelength of light and be linked with appropriate fiber. There are
two categories of fiber optic cable: "multi-mode" and "single-mode." Note that until
recently, the cable used with 820nm wavelength light was offered only in multi-mode while
1300nm wavelength light uses both single and multi-mode compatible cable. Cable
compatible with 1550nm wavelength light is offered only in single mode.
7.1.1 Wavelengths of light
Note that both devices must use the same wavelength of light.
Multi-Mode Single-Mode
820nm X X
1300nm X X
1550nm N/A X