The 100BaseT standard retains 10BaseT's critical 100-meter maximum cable length between the hub and desktop. With 100BaseT, the maximum number of repeater Hups is two. This is due to the accelerated Ethernet data rate , which requires a reduction in network diameter in order to detect collisions. TO build a two-repeater-stack LAN , Class II repeaters must be used. In a single-repeater-stack LAN, Class I or Class II repeaters can be used. Whether the repeater is Class I or Class II is determined by how much delay is added by the repeater. Most stackable repeater are class I , while non-stackables are usually Class II.

With 100BaseT,the maximum network diameter is approximately 205 meters with UTP cable and 412 meters with fiber cable. By contrast ,a maximum of four repeater hups is allowed for 10BaseT, providing a maximum network diameter of 500 meters on UTP.

The 100BaseT standard is comprised of five component specifications - Media Access Control(MAC) layer, Media Independent Interface(MII) layer and the three physical layers ( 100BaseTX, 100BaseT4 and 100Base FX). 100BaseTX uses the same IEEE 802.3 CSMA/CD MAC protocol layer as 10BaseT and a similar star topology. There are three distinct cabling variations in the 100BaseT standard.

They are: *100BaseTX for two-pair data grade Category 5 UTP or Type 1 STP

*100BaseT4 for four-pair voice and data grade Category 3,4 or 5 UTP

*100BaseFX for 2-strand multimode fiber

Media Access Control (MAC) Layer
The MAC layer is based on the same CSMA/CD protocol as 10Mbps Ethernet. The only difference is that it runs 10times faster.

Media Independent Interface (MII) Layer
The MII is a new specification that defines a standard interface between the MAC layer and any of the three physical layers (100BaseTX, 100BaseT4 or 100BaseFX). It is capable of supporting both 10Mbos and 100Mbps data rates.

100BaseTX Physical Layer
This physical layer defines the specification for 100BaseT Ethernet over two pairs of Category 5 UTP or Type 1 STP twisted pair wire. With one pair for transmit and the other for receive, the wiring scheme is identical to that used for 10BaseT Ethernet. The UTP connector, an RJ-45, is also identical to the one used for 10BaseT Ethernet. However, the punch-down blocks in the wiring closet must be category 5 certified.

100BaseT4 Physical Layer
This physical layer defines the specification for 100BaseT Ethernet over four pairs of either Category 3,4 or 5 UTP wire. With this signaling method, three wire pairs are used for transmit and receive, while the fourth pair listens for collision. The two additional pairs of bi-directional wired use the four vacant pins on the connector. An RJ-45 connector is used, wired the same way as it is for 10BaseT.

Network Diameter
Due to its increased speed and adherence to the EIA/TIA 568 wiring rules, the maximum diameter of a Fast Ethernet twisted-pair (100BaseTX or 100BaseT4) network is 205 meters.

Repeater Classes
All 10BaseT repeaters are considered to be functionally identical. Fast Ethernet repeaters, on the other hand, are divided into two distinct types: Class I and Class II.

• A Class II repeater typically connects identical media to the same collision domain. Since translations are not performed , this repeater has been assigned a timing budget that is small enough so two Class II repeaters can exist within a single collision domain.

Today, some manufacturers, Lantech included, offer Class I repeaters that can be cascaded with the latest technology.