Information Technology Reference
In-Depth Information
for hubs, switches, and NICs are limited, and the prices are higher. Clearly, the more
popular 10/100BaseT (incorporating 2-pair 100BaseTX) version is the dominant
technology.
If you are installing a new cabling system, you should not use the existence of
this type of high-speed connection as an excuse to put in Category 3 links. Full
Category 5e installations are not that much more expensive than new Category 3
ones, and you can move to gigabit technologies that require Category 5e performance.
The wiring pattern for 100BaseT4 is shown in Fig. 2.7. All four pairs are
required for this topology, so you cannot use it if you have split your cable into 2-
pair jacks. However, it will run fine on any standard TIA/EIA-568-A cabling system.
The four pairs of a 100BaseT4 connection are used in a clever manner. The tra-
ditional pairs for transmit and receive are maintained on the same pins as the lower-
speed 10BaseT network, but the other two pairs are used alternately for transmit or
for receive when sending data. Thus, at any one time, three pairs are available for
either transmit or receive. This technique is coupled with an advanced line coding
to achieve the high bit rate at low symbol rates. The 100BaseT4 technology suffers
from the same distance and repeater limitations as 100BaseTX and has the same
speed buffering problem if mixed with slower networks.
Ethernet standards allow the use of fiber-optic cable at 10, 100, and 1000 Mbps.
Emerging standards will even allow the speed to grow to 10 Gbps. This section
Name
Signal purpose
Abbrev
Data1
Dedicated Transmit
Tx_D1
1
Data1
Dedicated Transmit
Tx_D1
2
Data2
Dedicated Receive
Rx_D2
3
Data3
Bidirectional Data3
BI_D3
4
Data3
Bidirectional Data3
BI_D3
5
Data2
Dedicated Receive
Rx_D2
6
Data4
Bidirectional Data4
BI_D4
7
Data4
Bidirectional Data4
BI_D4
8
8-pin Modular jack
(front view)
100BaseT4
Medium-dependent
interface
FIGURE 2.7
100BaseT4 Interface wiring pattern.
