"INTRODUCTION At the March 1987 meeting@ the T1M1.3 Working Group for Testing and Operations Support Systems determined that a study and Technical Report should be made on the subject of the testing and operations impact of using two mutually exclusive line codes. Study work was initiated shortly thereafter and continued through August 1987. This report contains the findings and opinions of interested contributors from the T1.M1 Technical Subcommittee and from other organizations whose opinions were solicited. These contributors and their organizations are identified elsewhere in this document. The objective of the study were to identify the expected configurations of DS1 circuits@ decide where equipment with line code option capabilities would be located@ describe the expected behavior of the line and data when the option switches were improperly set and make recommendations to T1M1@3 regarding the draft Technical Report. The implicit objective is to identify the size and scope of the issue and create an awareness within the industry of the operational impacts. This report has been prepared from the viewpoint of a ""carrier@"" that is@ an organization or group of organization which will be designing@ implementing and operating networks which contain equipment capable of operating in either the B8ZS or traditional AMI mode. As indicated in the text of this report and the reference list@ some background and tutorial information has been excerpted from documents issued by Technical Subcommittees T1M1 and T1X1. Much of this information is included to profile the extent of the application. In order to establish a suitable framework for discussion of the incompatibility of mixed line codes@ Section 2.0 contains a synopsis of the behavior of both the traditional AMI codec and the B8ZS codec. Section 2.0 also contains the test results obtained by the Ad Hoc Group at a New York Telephone laboratory. Section 3.0 discusses the testing techniques and equipment in use today@ the limitations thereof@ and possible future techniques which will enable the operations personnel to verify option settings. Section 3.0 is divided into sub-sections to assist technical personnel in the identification of the trouble. Section 4.0 deals with the cross-boundary administrative concerns associated with the use of equipment having the capability of operating in either mode. Section 5.0 contains the recommendations of the T1M1.3 Testing and Operations Support Systems Working Group. Section 6.0 lists the documentation and references utilized in this Technical Report."