Illinois Administrative Code
Title 83 - PUBLIC UTILITIES
Part 730 - STANDARDS OF SERVICE FOR LOCAL EXCHANGE TELECOMMUNICATIONS CARRIERS
Subpart E - STANDARDS OF QUALITY OF SERVICE
Section 730.520 - Interoffice Trunks

a) Local interoffice trunks and intraoffice trunks, interoffice toll trunks, and the intertoll trunk and any related switching components shall be engineered so that at least 98% of calls shall not encounter an All Trunks Busy (ATB) condition and at least 98% of properly dialed incoming interMSA calls, during the busy hour, shall receive ringing signal, station busy tone, or intercept (other than ATB) on the first attempt. When the completion rate falls below 98% for three consecutive months, corrective action shall be initiated and such action reported to the Commission.

b) For purposes of subsection (a), the information required to be reported shall be calculated by capturing total call attempts (local, toll, DDD, or inter/intraoffice) and calls that do not encounter an ATB condition that are going through trunk groups controlled by the reporting entity during the busy hour. Calls that do not encounter an ATB condition should be divided by Total Trunk Attempts to derive the percent of calls completed without encountering an ATB. The calculation should be performed for each base unit and all remotes that home on each base. Measurements for all of the base and remote units should be added to provide a statewide basis.