s. 17. If no sequence numbers are used with frame relay, how are frames kept in sequential order? 18. How does an end-user know that a frame or frames have been lost or discarded? REFERENCES 1. Interface between Data Terminal Equipment (DTE) and Data Circuit-Terminating Equipment (DCE) for Terminals Operating in the Packet Mode and Connected to the Public Data Networks by Dedicated Circuit, ITU-T Rec. X.25, Helsinki, 1993. 2. Internet Protocol, RFC 791, DDN Network Information Center, SRI International, Menlo Park, CA, 1981. 3. Transmission Control Protocol, RFC 793, DDN Network Information Center, SRI International, Menlo Park, CA, 1981. 4. Packet-Switched Signaling System between Public Networks Providing Data Transmission Ser- vices, ITU-T Rec. X.75, Helsinki, 1993. 5. Internet Protocol Transition Workbook, SRI International, Menlo Park, CA, 1982. 6. Assigned Numbers, RFC 1060, DDN Network Information Center, SRI International, Menlo Park, CA, 1990. 7. An Ethernet Address Resolution Protocol, RFC 826, DDN Network Information Center, SRI International, Menlo Park, CA, 1984. 8. A Reverse Address Resolution Protocol, RFC 903, DDN Network Information Center, SRI International, Menlo Park, CA, 1984. 9. Military Standard, Transmission Control Protocol, MIL-STD-1778, U.S. Dept. of Defense, Washington, DC, 1983. 10. IEEE Standard Dictionary of Electrical and Electronic Terms, 6th ed., IEEE Std. 100-1996, IEEE, New York, 1996. 11. ISDN User-Network Interfaces-Interface Structure and Access Capabilities, CCITT Rec. I.412, Fascicle III.8, IXth Plenary Assembly, Melbourne, 1988. 12. ISDN Network Architecture, CCITT Rec. I.324, ITU Geneva, 1991. 13. Framework of Frame Mode Bearer Services, ITU-T Rec. I.122, ITU Geneva, 1993. 14. Frame Mode Bearer Services, CCITT Rec. I.233, ITU Geneva, 1992. 15. ISDN Signaling Specification for Frame Relay Bearer Service for Digital Subscriber Signaling System No. 1 (DDS1), ANSI T1.617-1991, ANSI, New York, 1991. REFERENCES 16. ISDN Data Link Layer Service for Frame Relay Mode Bearer Servi