 are two toll connecting trunks in a built-up toll connection, by definition. The remaining intervening toll trunks will operate at 0 dB loss/0 dB gain; thus the 6-dB total loss. By the following, we can see that the 0 TLP concept still hangs on. We quote from Telecommunication Transmission Engineering, Vol. 3 (AT&T, New York): It is desirable in the fixed loss network to retain the 6-dB loss for test conditions SO that all trunks have an EML (expected measured loss) of 6 dB. To accomplish this, the transmitting and receiving test equipment at digital offices (exchanges) must be equipped with 3-dB pads with analog-digital converters. Because of the use of 3-dB test pads, the No. 4 ESS (ATT digital toll exchange) can be considered at -3 TLP even though signals are in digital form. Since the path through the machine (digital switch) is lossless, the 3 TLP applies to the incoming as well as the outgoing side of the machine, a feature unique to digital switching machines. C.12 EIRP C.11 dBi The dBi is used to quantify the gain of an antenna. It stands for dB above (or below) an isotropic. If it is above, we will often use the plus (+) sign, and when below an isotropic, we will use a minus (-) sign. An isotropic is an imaginary reference antenna with uniform gain in all three dimensions. Thus, by definition, it has a gain of 1 dB or 0 dB. In this text, and in others dealing with commercial telecommunications, all antennas will have "positive" gain. In other words, the gain will be greater than an isotropic. For example, parabolic dish antennas can display gains from 15 dBi to over 60 dBi. C.11.1 dBd The dBd is another dB unit used to measure antenna gain. The abbreviation dBd stands for dB relative to a dipole. This dB unit is widely used in cellular and PCS radio technology. When compared to an isotropic, the dBd unit has a 2.15-dB gain over an isotropic. For example, +2 dBd = +4.15 dBi. C.12 EIRP EIRP stands for "effective isotropically radiated power." We use the term to express how much transmitted power is radiat