Ethernet - Computer Busses - page 434

Table 26.3 Cable connections for 100BASE-TX

Pin Cable colour Cable colour Pair

1 white/orange white/orange Pair 4

2 orange/white orange/white Pair 4

3 white/green white/green Pair 3

4 blue/white blue/white Pair 3

5 white/blue white/blue Pair 1

6 green/white green/white Pair 1

7 white/brown white/brown Pair 2

8 brown/white brown/white Pair 2

Migration to fast Ethernet
If an existing network is based on standard Ethernet then, in most cases, the best network
upgrade is either to fast Ethernet or 100VG-AnyLAN. As the protocols and access methods
are the same, there is no need to change any of the network management software or applica-
tion programs. The upgrade path for Fast Ethernet is simple and could be:

• Upgrade high data rate nodes, such as servers or high-powered workstations to Fast
Ethernet.
• Gradually upgrade NICs (network interface cards) on Ethernet segments to cards which
support both 10BASE-T and 100BASE-T. These cards automatically detect the trans-
mission rate to give either 10 or 100 Mbps.

The upgrade path to 100VG-AnyLAN is less easy as it relies on hubs and, unlike Fast
Ethernet, most NICs have different network connectors, one for 10BASE-T and the other for
100VG-AnyLAN (although it is likely that more NICs will have automatic detection). A
possible path could be:

• Upgrade high data rate nodes, such as servers or high-powered workstations to 100VG-
AnyLAN.
• Install 100VG-AnyLAN hubs.
• Connect nodes to 100VG-AnyLAN hubs and change over connectors.

It is difficult to assess the performance differences between Fast Ethernet and 100VG-
AnyLAN. Fast Ethernet uses a well-proven technology, but suffers from network contention.
100VG-AnyLAN is a relatively new technology and the handshaking with the hub increases
delay time. The maximum data throughput of a 100BASE-TX network is limited to around
50 Mbps, whereas 100VG-AnyLAN allows rates up to 96 Mbps. 100VG-AnyLAN allows
possible upgrades to 400 Mbps.