must wait for at least T + TB seconds until it is capable of detecting a worst-case collision. When the worst-case scenario occurs, we can assume with very near precision that TA=T= = = t. Because the slot time represents the one-way delay, we can express it as a function of total delay as follows: 2 X (slot time) = t or simply as 2t = t t This means that the one-way slot time of 512 bits represents half the maximum delay before the network experiences late collisions. Thus, the one-way delay must be doubled to 1024 bit times, which results in an engineering design constraint. While an Ethernet or Fast Ethernet Ethernet or Fast Ethernet LAN Stations farthest apart Figure 5.8 The Ethernet and Fast Ethernet network diam- eter is a function of the propagation delay between the two stations farthest apart on the network. Chapter Five network will not collapse when this design constraint is exceeded, late collisions will increase. Because collisions result in the execution of a random backoff algorithm, this adversely effects throughput and explains why you should observe network standards. USING THE VELOCITY OF PROPAGATION We can use the velocity of propagation (VoP) to determine the effect of the slot time constraint on the network diameters of Ethernet and Fast Ethernet networks. The velocity of propagation represents the speed of a signal traveling down a cable as a percentage of the speed of light in a vacuum. The speed of light in a vacuum is 186,000 mi/s (miles per second) or approximately 300,000,000 m/s (meters per second). This is equivalent to 0.3 m/ns or 300 m/us. COPPER MEDIA In a copper-medium environment the VoP represents 60 to 70 percent of the speed of light in a vacuum. For category 5 cable, which is used primarily by Ethernet and Fast Ethernet, the VoP is 69 per- cent of the speed of light in a vacuum. This means that an electrical sig- nal travels along a category 5 cable at 0.3 m/us X 69 or approximately 0.21 m/ns. For anyone accustomed to thinking in feet, this is equivalent to approximately 8 i