Appendix
33
Appendix 1 Full-duplex and Half-duplex
There are two types of Ethernet communication modes: full-duplex and half-duplex. The maximum
transmission distances and optical fiber lengths are different for the two modes.
-
Full-duplex
This mode allows simultaneous send and receive. A station can receive data from other station while
sending data.
-
Half-duplex
This mode allows either send or receive at one time. A station can not receive data from other station while
sending data.
Station
Switching Hub
TX
RX
Switching Hub
Full-duplex
Port
Full-duplex
Port
Send
Receive
Full-duplex
Port
Full-duplex
Port
Send
Receive
Figure A1.1 Full-duplex Communication Mode
Station
Shared Hub
Half-duplex
Port
Half-duplex
Port
Send
Receive
TX
RX
Switching Hub
Send
Receive
Half-duplex
Port
Half-duplex
Port
Figure A1.2 Half-duplex Communication Mode
Since the 10M Ethernet contains coaxial cable segments, half-duplex is basically used. Since the 100M
Ethernet consists of twisted pair cables and optical fibers (in pair), full-duplex may be used.
For the half-duplex communication mode, the signal propagation time from one end of the network to the other
for collision detection. Thus, the maximum transmission distance of the network is limited (2.5 km).
Since send and receive can be performed simultaneously in the full-duplex mode, there is no concept of collision
and the maximum transmission distance is not limited. Thus, the maximum cable length for two hubs or a hub
and a station connected via the full-duplex communication mode is determined according to the attenuation of
the signal in the cable.
The maximum cable length for optical fiber is 400m for the half-duplex communication mode due to collision
detection. In the full-duplex mode, collision detection doesn’t affect, and the maximum cable length is 2km due
to signal attenuation. The maximum cable length for twisted pair cables is 100m for both full- and half-duplex.
It is based on the effect of signal attenuation.
