Copyright Goodheart-Willcox Co., Inc. 50 Networking Fundamentals Original Signals Interference Added to Attenuation Signals After Amplification and Filtering Figure 2-2 The effects of filtering analog and digital signals. Top—Analog and digital signals in their original form. Middle—Analog and digital signals affected by interference and attenuation. Bottom— Analog and digital signals amplified and filtered. Note the fidelity of the digital signal in comparison to the analog signal after amplification and filtering. Goodheart-Willcox Publisher voltage (amplitude) and cannot be reproduced by the repeater because the repeater only generates two levels of signal strength. Excessively strong interference, however, can be impossible to fi lter from a digi- tal signal. Interference strength is directly related to the distance from the digital sig- nal and the power of the source producing the interference. For example, a portable telephone may interfere with a digital signal at a close proximity of fi ve to 10 feet but not generate suffi cient signal strength at 30 feet to interfere with the digital signal. Latency Latency is the amount of time it takes a signal to travel from its source to its destina- tion. A general cause of latency is network equipment along the signal’s path. Some networking devices regenerate, or reshape, a digital signal after it is received. For ex- ample, a repeater is used to extend the maximum distance that a signal can normally travel by reshaping the signal. A digital signal may travel through several repeaters before reaching its destination, thus slowing the time it takes the signal to reach its destination. Latency will be discussed in more detail in Chapter 12. Th ere is normally a maximum amount of time a packet is allowed to circulate through a network before it is destroyed. If the overall latency is too great, the packet is dropped from the network. However, this is not measured by time, but rather how many intermediate stops are between the source and the destination. Th is is defi ned as hops. Th e maximum number of hops allowed is referred to as the time to live (TTL). If a particular network packet exceeds the allocated TTL, it is removed from the network to prevent it from circulating forever. Data Transmission Data transmission terminology and concepts are often referenced in network stan- dards and equipment specifi cations. A good understanding of data transmission ter- minology will help you master some of the most diffi cult concepts of networking. Much of the original network terminology has its roots in the fi eld of electronics. 5.3 NET 1.8 NET