100Base-T Ethernet are 100Base-TX, 100Base-FX, and 100Base-T4. A slightly different specification, called 100VG-AnyLAN (IEEE 802.12) competes with 100-Base-T. The key difference among the 100-Mbps products is in the kind of cable they use and, in the case of 802.12, how well they cope with the needs of time-sensitive video packets. Within the 100Base-T family, the cabling differences are as follows 100Base-TX requires Category 5 UTP, 100Base-FX requires fiber optic cable, and 100Base-T4 uses Category 3, 4 or 5 UTP, but four pairs of wire are required for each node. Over unshielded twisted pair cable, 100Base-T can support only two repeater hops (compared to 10Base-T's three to five hops) and its theoretical collision domain is limited to only 205 meters-less than one tenth that of 10Base-T. These limits can be overcome by deploying stackable hubs and switches. Although estimates vary, it is safe to say that Category 3 UTP is installed in more than 50% of the telecommunications networks in North America. That simple fact makes 100Base-T4 a viable option for networks with pervasive Category 3 cable. 100Base-T4 needs four pair. In 100Base-T4 implementations, it is important that every wire and every connection in every cable is good. This is not always the case. Although 100Base-T4 is an easy step to take, the market shows little interest in it. 100Base-TX requires two pairs of Category 5 wires. The Category 5 requirement often forces organizations that select to pay for a new cable system. In various tests, 100Base-TX has been proved to handle increasing traffic loads much more effectively than 10Base-T. For instance, it is possible to run it at loads of up to 70% before any signs of congestion begin to appear. To lessen the impact of upgrading an entire network to Category 5 cable, many of the Video Communications: The Whole Picture 100Base-TX vendors are shipping adapters and hubs that can support both 100Base- TX and 100-Base-T4. Because all 100Base-T solutions use the same Ethernet packets, no extra bridging ha