m 0.001 to 0.05 and from 1 to 49 trunks. The table uses traffic-intensity units UC (unit call) and TU (traffic unit), where TU is in erlangs assuming BH conditions and UC is in CCS (cent-call-seconds). Remember that 1 erlang = 36 CCS (based on a 1-hour time interval). To exemplify the use of Table 4.1, suppose a route carried 16.68 erlangs of traffic with a desired grade of service of 0.001; then 30 trunks would be required. If the grade of service were reduced to 0.05, the 30 trunks could carry 24.80 erlangs of traffic. When sizing a route for trunks or an exchange, we often come up with a fractional number TRANSMISSION AND SWITCHING: CORNERSTONES OF A NETWORK Table 4.1 Trunk-Loading Capacity, Based on Erlang B Formula, Full Availability Grade of Grade of Grade of Grade of Grade of Grade of Service Service Service Service Service Service 1 in 1000 1 in 500 1 in 200 1 in 100 1 in 50 1 in 20 Trunks 0.001 0.002 0.005 10.63 11.54 10.66 12.46 10.44 11.49 13.38 10.33 11.23 12.33 14.31 10.07 11.09 12.03 13.18 15.25 10.11 10.79 11.86 12.84 14.04 16.19 10.81 11.53 12.63 13.65 14.90 17.13 11.52 12.27 13.42 14.47 15.76 18.08 12.24 13.01 14.20 15.29 16.63 19.03 12.97 13.76 15.00 16.12 17.50 19.99 13.70 14.52 15.80 16.96 18.38 20.94 14.44 15.28 16.60 17.80 19.26 21.90 15.18 16.05 17.41 18.64 20.15 22.87 15.93 16.83 18.22 19.49 21.04 23.83 16.68 17.61 19.03 20.34 21.93 24.80 17.44 18.39 19.85 21.19 22.83 25.77 18.20 19.18 20.68 22.05 23.73 26.75 18.97 19.97 21.51 22.91 24.63 27.72 19.74 20.76 22.34 23.77 25.53 28.70 20.52 21.56 23.17 24.64 26.43 29.68 21.30 22.36 24.01 25.51 27.34 30.66 22.03 23.17 24.85 26.38 28.25 31.64 22.86 23.97 25.69 27.25 29.17 32.63 23.65 24.78 26.53 28.13 30.08 33.61 24.44 25.60 27.38 29.01 31.00 34.60 25.24 26.42 28.23 29.89 31.92 35.59 26.04 27.24 29.08 30.77 32.84 36.58 26.84 28.06 29.94 31.66 33.76 37.57 27.64 28.88 30.80 32.54 34.68 38.56 28.45 29.71 31.66 33.43 35.61 39.55 29.26 30.54 32.52 34.32 36.53 40.54 30.07 31.37 33.38 35.21 37.46 41.54 30.88 32.20 34.25 36.11 38.39 42.54 31.69 33.04 35.