 circuit multiplexing/demultiplexing using the address field of the frame. 3. Inspection of the frame to ensure that it consists of an integer number of octets prior to zero bit insertion or following zero bit extraction. 4. Inspection of the frame to ensure it is not too short or too long. 5. Detection of transmission, format, and operational errors. A frame received by a frame handler may be discarded if the frame: 1. Does not consist of an integer number of octets prior to zero bit insertion or fol- lowing zero bit extraction. 2. Is too long or too short. 3. Has an FCS that is in error. The network will discard a frame if it: 1. Has a DLCI value that is unknown; or 2. Cannot be routed further due to internal network conditions. A frame can be discarded for other reasons, such as exceeding negotiated throughput. Section 12.5 is based on ANSI standards T1.618-1991, T1.606-1990, and T1.606a-1992 (Refs. 17, 18, 20). REVIEW EXERCISES 1. How does a processor know where a frame's field boundaries are? 2. Even though TCP/IP predates OSI, in what OSI layers would we expect to find TCP and IP? 3. What is the purpose of ARP (address resolution protocol)? 4. What is the primary function of IP? 5. What is the function of a router in an IP network? 6. What are the three types of routing carried out by an IP routing table? ENTERPRISE NETWORKS II: WIDE AREA NETWORKS 7. How is ICMP used as an adjunct to IP? 8. What is the term used in TCP//IP parlance for segmentation? 9. What important mechanisms does TCP offer IP with its potentially unreliable services? What is the purpose of the three-way handshake? What does a frame relay network do with errored frames. 12. Frame relay operation derives from which predecessor? 13. There are six possible causes for declaring a frame's relay frame invalid. Name four of them. 14. Discuss the use of CLLM as an alternative for congestion control? Give at least two advantages of CLLM over FECN/BECN over congestion control? 16. Name some actions a congested node can take to alleviate the problem