h SDH, the payload in octets is not an integer multiple of cell length, and thus a cell may cross an STS cell boundary. This mapping concept is shown in Figure 20.21. The H4 pointer can indicate where the cells begin inside an STS frame. Another approach is to identify cell headers, and thus the first cell in the frame. REVIEW EXERCISES 1. What are the two major similarities of frame relay and ATM/B-ISDN? What are some radical differences with frame relay and other data transmission protocols/techniques? 3. ATM offers two basic services. What are they? Relate each service to at least one medium to be transported/switched. 4. Compare signaling philosophy with POTS and data. 5. Leaving aside Bellcore, what are the three standardization bodies for ATM? 6. Describe the ATM cell, its length in octets, the length of the header (and payload). Indicate variants to the lengths in octets. 7. Describe two functions of the HEC field. 8. What is the purpose of the CLP bit? 9. Why must there be a constant cell flow on an ATM circuit? 10. What is the principal function of the ATM layer? 11. What are "F4 flows?" 12. What is the principal purpose of the ATM adaptation layer? What is the principal use of AAL-1? 14. What is the principal application of AAL3/4? ASYNCHRONOUS TRANSFER MODE 15. What does a VPI identify? 16. What service classification parameters is the AAL based on? 17. Where are routing functions of virtual channels done? 18. What happens to cells found with errors in their headers? 19. Name three of the four ways the setup and release of VCCs at the UNI can be performed. 20. Name five of the seven ATM unique quality of service (QoS) items. 21. Cell transfer delay happens at an ATM switch. What is the cause of the delay? 22. Give three causes of CDV (cell delay variation). 23. Name and explain two effects of CDV. 24. What is user/network parameter control (UPC/NPC)? ATM cells are transported on DS1, E1 hierarchies, SONET/SDH hierarchies? With one exception, what is an unfortunate outcome of the 53-octet cell? REFERENC