Example of How to Determine Grade of Service

For example, you have a system with 12 ports. Over the course of 54 business days, you record the value in the Maximum Average Ports in Use field on the Feature Daily Traffic screen. You add the five numbers together and divide by five to get an average of 7.25. You then look in the Port column in the table for the row that starts with 12 (the number of ports in this sample system). Looking across that row, note that the value that is equal to or just larger than 7.25 is 7.38. The GOS at the top of that column is 0.05.

You can also use the table to determine the number of ports required for a system under the present load. For example, if a 0.03 GOS is desired, look for the column with the heading of 0.03 GOS. Look down that column to find the number equal to or just larger than the value in the Maximum Average Ports in Use field from the Feature Daily Traffic screen. Then look across to the value in the left-hand column of that row to determine the number of ports required for a 0.03 GOS.

To continue this example, assume that your Maximum Average Ports in Use is 45. Looking down the 0.03 GOS column, the closest value to 45 is 45.38. Looking leftward to the corresponding Port column, you see that 56 ports are required to maintain a 0.03 GOS. Note that ports are always sold in increments of two, so if the number of ports shown is an odd number, round it up by one.

Port Capacity in Erlangs (Avg. Ports in Use) at Various GOS

Ports	0.01 GOS	0.02 GOS	0.03 GOS	0.04 GOS	0.05 GOS	0.06 GOS	0.08 GOS	0.10 GOS
2	0.16	0.23	0.29	0.33	0.38	0.41	0.48	0.54
3	0.47	0.61	0.71	0.79	0.86	0.92	1.03	1.12
4	0.89	1.09	1.22	1.34	1.43	1.51	1.65	1.78
5	1.38	1.64	1.81	1.94	2.07	2.17	2.35	2.49
6	1.92	2.24	2.44	2.60	2.74	2.86	3.06	3.22
7	2.51	2.86	3.11	3.31	3.44	3.58	3.81	4.00
8	3.14	3.53	3.81	4.00	4.17	4.33	4.58	4.78
9	3.78	4.22	4.53	4.75	4.94	5.08	5.36	5.58
10	4.44	4.92	5.25	5.50	5.69	5.89	6.17	6.42
11	5.14	5.67	6.00	6.28	6.50	6.67	6.97	7.25
12	5.83	6.39	6.78	7.06	7.28	7.47	7.81	8.08
13	6.56	7.17	7.56	7.83	8.08	8.31	8.64	8.92
14	7.31	7.92	8.33	8.64	8.92	9.14	9.50	9.78
15	8.03	8.69	9.14	9.47	9.72	9.97	10.33	10.64
16	8.81	9.50	9.94	10.28	10.56	10.81	11.19	11.53
17	9.56	10.29	10.76	11.12	11.41	11.65	12.06	12.39
18	10.34	11.09	11.58	11.95	12.25	12.51	12.93	13.27
19	11.12	11.91	12.41	12.79	13.10	13.37	13.80	14.16
20	11.91	12.72	13.25	13.64	13.96	14.23	14.68	15.05
21	12.71	13.55	14.09	14.49	14.82	15.10	15.56	15.94
22	13.51	14.38	14.93	15.35	15.69	15.98	16.45	16.84
23	14.32	15.21	15.78	16.21	16.56	16.85	17.34	17.73
24	15.14	16.05	16.64	17.08	17.44	17.74	18.23	18.64
25	15.96	16.90	17.50	17.95	18.31	18.62	19.13	19.54
26	16.78	17.75	18.36	18.82	19.20	19.51	20.03	20.45
27	17.61	18.60	19.23	19.70	20.08	20.40	20.93	21.36
28	18.44	19.46	20.10	20.58	20.97	21.30	21.84	22.28
29	19.28	20.32	20.97	21.46	21.86	22.20	22.75	23.19
30	20.12	21.18	21.85	22.35	22.76	23.10	23.66	24.11
31	20.97	22.05	22.73	23.24	23.65	24.00	24.57	25.03
32	21.82	22.92	23.61	24.13	24.55	24.90	25.48	25.95
33	22.67	23.79	24.50	25.02	25.45	25.81	26.40	26.87
34	23.53	24.66	25.38	25.92	26.35	26.72	27.32	27.80
35	24.38	25.54	26.27	26.82	27.26	27.63	28.24	28.72
36	25.25	26.42	27.17	27.72	28.17	28.54	29.16	29.66
37	26.11	27.31	28.06	28.63	29.08	29.46	30.08	30.59
38	26.98	28.19	28.96	29.53	29.99	30.38	31.01	31.52
39	27.84	29.08	29.86	30.44	30.90	31.29	31.93	32.45
40	28.72	29.97	30.76	31.34	31.82	32.21	32.86	33.38
41	29.59	30.86	31.66	32.26	32.73	33.13	33.79	34.32
42	30.47	31.76	32.57	33.16	33.65	34.06	34.72	35.25
43	31.35	32.65	33.47	34.08	34.57	34.98	35.65	36.19
44	32.23	33.55	34.38	34.99	35.49	35.91	36.59	37.13
45	33.11	34.45	35.29	35.91	36.41	36.83	37.52	38.07
46	33.99	35.35	36.20	36.83	37.33	37.76	38.45	39.01
47	34.88	36.25	37.11	37.75	38.26	38.69	39.39	39.96
48	35.77	37.16	38.02	38.67	39.19	39.62	40.33	40.90
49	36.66	38.06	38.94	39.59	40.11	40.55	41.27	41.84
50	37.55	38.97	39.85	40.51	41.04	41.48	42.21	42.79
51	38.44	39.88	40.77	41.44	41.97	42.42	43.15	43.73
52	39.33	40.79	41.69	42.36	42.90	43.35	44.09	44.68
53	40.23	41.70	42.61	43.29	43.83	44.29	45.03	45.63
54	41.13	42.61	43.53	44.22	44.77	45.23	45.98	46.58
55	42.03	43.52	44.45	45.15	45.70	46.17	46.92	47.53
56	42.93	44.44	45.38	46.08	46.64	47.10	47.86	48.48
57	43.83	45.35	46.30	47.01	47.57	48.04	48.81	49.43
58	44.73	46.27	47.23	47.94	48.51	48.98	49.76	50.38
59	45.64	47.19	48.16	48.87	49.44	49.92	50.70	51.33
60	46.54	48.11	49.09	49.81	50.38	50.86	51.65	52.28
61	47.45	49.03	50.01	50.74	51.32	51.81	52.60	53.24
62	48.36	49.95	50.94	51.67	52.26	52.75	53.55	54.19
63	49.27	50.87	51.87	52.61	53.20	53.70	54.50	55.15
64	50.18	51.79	52.80	53.55	54.14	54.64	55.45	56.10
65	51.09	52.72	53.73	54.48	55.09	55.59	56.40	57.06
66	52.00	53.65	54.67	55.42	56.03	56.54	57.35	58.01
67	52.91	54.57	55.61	56.37	56.97	57.48	58.31	58.97
68	53.83	55.50	56.54	57.31	57.92	58.43	59.26	59.93
69	54.75	56.43	57.48	58.25	58.86	59.38	60.21	60.88
70	55.66	57.36	58.41	59.19	59.81	60.33	61.17	61.84
71	56.58	58.29	59.35	60.13	60.75	61.28	62.12	62.80
72	57.50	59.22	60.29	61.07	61.70	62.23	63.08	63.76
73	58.42	60.15	61.22	62.01	62.65	63.18	64.04	64.72
74	59.34	61.08	62.16	62.96	63.60	64.13	64.99	65.68
75	60.26	62.02	63.10	63.91	64.55	65.08	65.95	66.64
76	61.18	62.95	64.04	64.85	65.50	66.03	66.91	67.61
77	62.10	63.88	64.99	65.80	66.44	66.99	67.87	68.57
78	63.03	64.82	65.92	66.74	67.40	67.94	68.82	69.53
79	63.95	65.75	66.87	67.69	68.35	68.90	69.78	70.49
80	64.88	66.69	67.81	68.64	69.30	69.85	70.74	71.45
81	65.80	67.62	68.76	69.59	70.25	70.80	71.70	72.42
82	66.73	68.56	69.70	70.54	71.20	71.76	72.66	73.38
83	67.66	69.50	70.64	71.48	72.16	72.71	73.62	74.34
84	68.59	70.44	71.59	72.44	73.11	73.67	74.58	75.31
85	69.51	71.38	72.54	73.39	74.06	74.63	75.54	76.28
86	70.44	72.32	73.48	74.33	75.02	75.58	76.51	77.24
87	71.37	73.26	74.43	75.29	75.97	76.54	77.47	78.20
88	72.30	74.20	75.38	76.24	76.93	77.50	78.43	79.17
89	73.23	75.15	76.32	77.19	77.88	78.46	79.39	80.14
90	74.17	76.09	77.27	78.14	78.84	79.42	80.36	81.10
91	75.10	77.03	78.22	79.09	79.79	80.38	81.32	82.07
92	76.03	77.97	79.17	80.05	80.75	81.34	82.28	83.04
93	76.97	78.91	80.12	81.00	81.71	82.30	83.25	84.01
94	77.90	79.86	81.07	81.96	82.67	83.26	84.22	84.97
95	78.84	80.80	82.02	82.91	83.63	84.22	85.18	85.94
96	79.77	81.75	82.97	83.87	84.58	85.18	86.14	86.91

We recommend that you monitor port usage regularly and plot it over time to anticipate traffic needs. We also recommend that you observe port capacities on a weekly basis on new systems or when you are adding new subscribers, and on a monthly basis on older systems.