THE THREE-DIGIT TELEPHONE NUMBER, 911, HAS BEEN DESIGNATED AS THE 'UNIVERSAL EMERGENCY NUMBER' FOR PUBLIC USE THROUGHOUT THE UNITED STATES TO REPORT EMERGENCIES AND REQUEST EMERGENCY ASSISTANCE. IN 1975, THE ILLINOIS LEGISLATURE MANDATED 911 SERVICE FOR ALL ILLINOIS COMMUNITIES BY DECEMBER 31, 1985. THIS DOCUMENT WAS PUBLISHED TO ASSIST TELEPHONE COMPANIES IN THIS EFFORT. A BASIC BACKGROUND ON THE 911 SYSTEM AND THE ILLINOIS 911 STATUTE IS FIRST PROVIDED. THE 911 SYSTEM CONSIDERATIONS ARE THEN EXAMINED BY DESCRIBING CENTRAL OFFICE MODIFICATIONS, NETWORK ARRANGEMENTS, TERMINAL EQUIPMENT, FEATURES, INTERCONNECTION ARRANGEMENTS WHERE REQUIRED, COMMUNITY CONTACT PROCEDURES, AND OTHER RELATED ITEMS. IN ADDITION, GUIDELINES ARE OFFERED ON PLANNING FOR 911 SERVICE, INSTALLING A 911 SYSTEM, AND 911 POST-INSTALLATION CONSIDERATIONS. THIS MANUAL IS ONE OF THREE VOLUMES THAT PROVIDE, RESPECTIVELY, A BASIS FOR STATE, LOCAL, AND TELEPHONE COMPANY PLANNING IN ILLINOIS. FOR THE OTHER TWO DOCUMENTS IN THIS SERIES, SEE NCJ-39541 AND NCJ-39542....DMC