ul completion of the handover, the UE sends a message to confirm the handover. After the successful completion of handover, PDCP SDUs may be re-transmitted in the target cell. This only CHAPTER 4 IEEE 802.16m System Operation and State Diagrams applies for data radio bearers using RLC-AM mode [17]. The source eNB should, for some time, maintain a context to enable the UE to return in case of handover failure. After having detected handover failure, the UE attempts to resume the RRC connection, either in the source or in another cell, using the RRC re-establishment procedure. This connection resumption succeeds only if the accessed cell is prepared, i.e., a cell of the source eNB or of another eNB which has performed handover preparation. References [1] IEEE Std 802.16-2009, IEEE Standard for Local and Metropolitan Area Networks - PART 16: Air Interface for Broadband Wireless Access Systems, May 2009. [2] P802.16m/D6, IEEE Standard for Local and Metropolitan Area Networks - Part 16: Air Interface for Broadband Wireless Access Systems - Advanced Air Interface, May 2010. [3] IEEE 802.16m-09/0034r3, IEEE 802.16m System Description Document. <http://ieee802.org/16/tgm/ index.html>, May 2010. [4] WiMAX Forum Network Architecture Release 1.5 Version 1 - Stage 2, Architecture. Tenets, Reference. Model. and. Reference. Points. <http://www.wimaxforum.org/resources/documents/technical/release>, September 2009. [5] WiMAX Forum Network Architecture Release 1.5 Version 1 - Stage 3, Detailed Protocols and Procedures. <http://www.wimaxforum.org/resources/documents/technical/release> September 2009. [6] Loutfi Nuaymi, WiMAX: Technology for Broadband Wireless Access, first ed., John Wiley & Sons, 2007. [7] Jeffrey G. Andrews, Arunabha Ghosh, Rias Muhamed, Fundamentals of WiMAX: Understanding Broadband Wireless Networking, first ed., Prentice Hall, 2007. [8] DRAFT-T23-005-R015v04-B_RSP, WiMAX Forum Mobile Radio Specification document [9] Truncated binary exponential backoff, Wikipedia, <http://en.wikipedia.org/wiki/Binary_exponenti