e cor- rectly count the different combinations of small and big calls using the resources. Each of the 15 states represents some combination of small calls and big calls that fit in the total resource of 7 units. Let us denote by 4s + 0b the state with four small calls and no big calls, and let 1s + 1b be the state with one small call and one big call. While both 5In fact, the ratio of usage may be greater than 10 because ISDN requires a lower bit error rate (BER) and, therefore, a higher Eb/No. This relationship is described in Chap. 29. Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Traffic Engineering for Voice and Data Capacity and Quality Principles 2,122 7,1111 Figure 23.3 Incorrect state diagram for two types of users. of these are using 4 units of resource, they are different states, and Fig. 23.4 shows them as different. While we can compute the equilibrium probabilities by solving 15 linear equations in 15 unknowns, there are some conclusions we can draw about the system without actually doing the calculation. We have marked with black circles the three states that block both small and big calls, 7s + 0b, 4s + 1b, and 1s + 2b. These are the states that use all 7 units of resource. The blocking rate for small calls is the sum of the equilibrium probabilities for the three black circles because these are the states that will block a small call. We have Users 2,122 2,111 Small Users Figure 23.4 State diagram for two types of users. Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Traffic Engineering for Voice and Data Traffic Engineering for Voice and Data marked with gray circles the five states that block big calls and not small calls, 6s + 0b, 5s + 0b, 3s + 1b