100VG-AnyLAN

100VG-AnyLAN

100VG-AnyLAN is defined in the IEEE 802.12 standard. IEEE 802.12 is a standard for transmitting Ethernet and Token Ring packets (IEEE 802.3 and 802.5) at 100 Mbps. 100VG-AnyLAN is sometimes called 100BASE-VG. The “VG” in the name stands for voice grade.

The section titled “Demand Priority” earlier in this chapter, discussed 100VG-AnyLAN’s demand priority access method, which provides for two priority levels when resolving media access conflicts.

100VG-AnyLAN uses a cascaded star topology, which calls for a hierarchy of hubs. Computers are attached to child hubs, and the child hubs are connected to higher-level hubs called parent hubs (see Figure 4.14).

The maximum length for the two longest cables attached to a 100VG-AnyLAN hub is 250 meters (820 ft). The specified cabling is Category 3, 4, or 5 twisted-pair or fiber-optic. 100VG-AnyLAN is compatible with 10BASE-T cabling.

Both 100VG-AnyLAN and 100BASE-X (see the following section) can be installed as a plug-and-play upgrade to a 10BASE-T system.