For the number of physical E1.0s (PCM systems) you need to look at the dimensioning by looking at the traffic profile. Between the SPCs you have the Link Sets. The maximum number of links you can have in a link set is 16. This assumes that each E1.0 takes around 40% load and the link balancing algorithm is used with the MSC/VLR.
If you have more than 16 links then you will experience a high degree of unbalanced traffic handling, some links will be overloaded whilst other links will be under utilised.
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