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Resource sizing
Issue 6 January 2008 205
Example 5: TDM and media processing usage
Consider the COI matrix in Table 32: Completed COI matrix for Example 4: Expanded COI
matrices on page 196 in Example 4: Expanded COI matrices. A set of nine cells corresponds to
calls originated in Site 1 and terminated in Site 1 (that is, the upper left group of nine cells,
arranged in a three-by-three submatrix). The uppermost and leftmost cell of those nine cells
indicates that the IP-to-IP call usage for Site 1 intrasite calls is 12.7 Erlangs. The other four cells
of those nine cells which fall in a row or column that is labeled “I” indicate that the total call
usage between IP endpoints and circuit-switched endpoints (including PSTN trunks) within Site
1 is (7.5 + 30.9 + 7.5 + 30.9) = 76.8 Erlangs. The remaining four cells of those nine cells indicate
that the total call usage between two circuit-switched endpoints (including PSTN trunks) within
Site 1 is (4.4 + 18.1 + 18.1 + 0) = 40.6 Erlangs. Analogous numbers for intrasite usages that
correspond to the other two sites are similarly derived.
Next, consider the three-by-three submatrix that corresponds to calls from Site 1 to Site 2. The
total call usage from Site 1 to Site 2 which involves an IP endpoint in Site 1 can be determined
by adding the three cell values of those nine cells that correspond to IP endpoints in Site 1.
Specifically, the total is (5.2 + 2.3 + 0) = 7.5 Erlangs. The total call usage from Site 1 to Site 2
which involves a circuit-switched endpoint (including PSTN trunks) in Site 1 can be determined
by adding the remaining six cell values of those nine. Specifically, that total is (3.1 + 1.4 + 0 + 0
+ 0 + 0) = 4.5 Erlangs.
The total call usage from Site 1 to Site 2 which involves an IP endpoint in Site 2 can be
determined by adding the three cell values of those nine that correspond to IP endpoints in Site
2. Specifically, the total is (5.2 + 3.1 + 0) = 8.3 Erlangs. And finally, the total call usage from Site
1 to Site 2 which involves a circuit-switched endpoint (including PSTN trunks) in Site 2 can be
determined by adding the remaining six cell values of those nine. Specifically, that total is (2.3 +
1.4 + 0 + 0 + 0 + 0) = 3.7 Erlangs. Analogous numbers for the other five combinations of
intersite usages are similarly derived. The results are shown in Table 33:
Re-categorization of
CURs from Table 32 on page 206.