estrial alterna- tives-is critical. Traditional Applications of Microwave One application associated with microwave is to replace the use of leased lines in a private network. Figure 2.3 shows a simple voice environment that initially made Microwave After Building A Building B Transmitter Transmitter Receiver Receiver Interface Interface Before Tie Trunks Tie Trunks Figure 2.3 Connecting PBXs by using microwave use of dedicated leased lines, also known as tie trunks, to link two PBXs in two dif- ferent buildings across town from one another. Because these tie trunks were billed on a monthly basis and were mileage sensitive, they were going to be a cost factor forever. Therefore, a digital microwave system was purchased to replace the tie trunks. This system provides capacity between the buildings and does away with the monthly cost of the leased lines. This setup is commonly used by multinode or multilocation customers (e.g., a health care facility with clinics and hospitals scat- tered throughout a state or territory, a university with multiple campuses, a retail location with multiple branches, a bank with multiple branches). Another key application of microwave is bypassing, which can be interpreted in multiple ways. Initially, this technique was used to bypass the local telecommu- nications company. With the introduction of competition in the long-distance marketplace, end users in the United States initially had choices about who would be their primary long-distance carrier (i.e., interexchange carrier). But to get to that carrier to transport the long-distance portion of the call, we still needed to get special local access trunks that led through the local operator to the competing interexchange provider. That meant paying an additional monthly fee for these local access trunks. In an attempt to avoid those additional costs, businesses began to bypass the local telephone company by simply putting up a digital Chapter 2 Traditional Transmission Media microwave system-a microwave tower with a shot directly t