ISDN and DDR for CCNAs This Tutorial attempts to cover all ISDN/DDR material likely to be on the CCNA exam. As a result of your ISDN studies, you should be able to answer any test questions about ISDN, PPP, and DDR. In addition to helping you pass the exam, learning ISDN well will give you a very important foundation for further progress in your internetworking knowledge and career. It's worth remembering that ATM, ISDN, and Frame Relay were all developed as part of the same standards process, a process that followed and drew from the OSI model development. Become a ZONE Subscriber and gain access to all Study Guides Author: David Wolsefer Technical Level: CCNA™ and CCIE Security & CSS1™ Date of Issue: 03-01-2023 Rating:     (Not Yet Rated)  Table of Contents  Tutorial  3 Sample Study Questions  25 Study Questions  Lab Scenario 1 Abstract  Lab Scenario 1  Lab Scenario 2 Abstract  Lab Scenario 2 Return to Study Guides