Doubling Bandwidth by Installing Full-Duplex
NOTE: The 10BASE-T specification requires two dedicated twisted
copper wire pairs for data transmission and reception.
This allows twisted
pair copper cable to be used either in half-duplex or full-duplex mode.
Legacy CSMA/CD Ethernet is Half-Duplex
Legacy Ethernet is a half-duplex communications system in which data
can be transferred in both directions but in which, at any given time, a
station is either transmitting or receiving. (On the original Ethernet
physical medium (coaxial cable) the same wire was used both for
transmission and reception.) With the current 10BASE-T physical media
(twisted pair), separate copper wire pairs are used for transmission and
for reception. Each station transmits to all stations and receives from all
stations. Since many devices share the medium, a device at the end of a
half-duplex Ethernet link listens for other transmissions or for collisions
when sending data, using the CSMA/CD protocol to prevent multiple
simultaneous transmissions on the medium.
Microsegmented Ethernet Link is Full-Duplex
Installing full-duplex allows the station attached to the Transition
Networks’ pocket switch to both transmit and receive at the same time.
In the microsegmented full-duplex switched Ethernet environment,
each station is connected to one dedicated switch port. Only the
attached station ever transmits to the switch (using the Transmit pair of
the cable), and only the switch ever transmits to the attached station
(using the Receive pair of the cable). There is never any contention for
the use of the medium, as in a standard half-duplex Ethernet
environment. Instead, both the station and the switch transmit at will,
using both directions simultaneously.
One advantage of this approach is that the full-duplex link can
theoretically provide twice the bandwidth of normal (half-duplex)
Ethernet. Since there are only two devices on a full-duplex link, the link
is not attempting to create a shared Ethernet channel capable of
supporting multiple devices. Therefore, there is no need to adhere to
the original Ethernet medium access control system. With no need to
use the CSMA/CD medium access control mechanism to share the
signal channel with multiple stations, a device at the end of a full-
duplex Ethernet link does not have to listen for other transmissions or
for collisions when sending data.
Connecting Twisted-Pair Copper Cable to RJ-45 Connector
(10BASE-T/100BASE-TX)
Though Category 3 cable is adequate for the 10BASE-T installation,
Category 5 cable is strongly recommended because Category 3 cable
can NOT be used for a later upgrade to 100BASE-TX. (Refer to the
cable specifications on page 27.)
10BASE-T AND THE ETHERNET COLLISION DOMAIN
•
Refer to the 5-Segment Rule (page 17) before installing half-
duplex 10BASE-T cable.
•
Installing full-duplex twisted-pair cable avoids collision
domain considerations; distances remain
≤
100 meters.
100BASE-TX AND THE FAST ETHERNET COLLISION DOMAIN
•
Refer to the 512-Bit Rule (page 18) before installing half-duplex
100BASE-TX cable.
•
Installing full-duplex twisted-pair cable avoids collision
domain considerations; distances remain
≤
100 meters.
•
A Fast Ethernet collision domain can have ONLY ONE CLASS I
repeater OR ONLY TWO CLASS II repeaters.
INSTALLING CABLE
To install 10BASE-T or 100BASE-TX cable:
1. Locate or build 10BASE-T or 100BASE-TX cables with the
following characteristics:
•
803.2 (10BASE-T) or 803.2u (100BASE-TX) compliant (See
pages 27, 28)
•
correct Straight-through or Crossover cable configuration
for site installation (See page 19)
•
male RJ-45 plug connectors installed at both cable ends.
2. Connect male RJ-45 plug connector at one end of 10BASE-T or
100BASE-TX cable to Transition Networks’ pocket switch RJ-45
jack connector.
3. Connect male RJ-45 plug connector at other end of 10BASE-T
or 100BASE-TX cable to network device RJ-45 jack connector.
Transition Networks’
Pocket Switch
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