TAILIEUCHUNG - Next Generation Mobile Systems 3G and Beyond phần 5

(CW) dựa trên thời gian backoff ngẫu nhiên để giảm xác suất va chạm • interframe không gian khác nhau (IFS) để ưu tiên các loại khác nhau của truyền • Lời cảm ơn khung để thực hiện dừng lại và chờ đợi ARQ • Yêu cầu gửi (RTS) và rõ ràng để gửi (CTS) bắt tay giải quyết | IP MOBILITY 141 Prehandover subnet change signaling is an optional part of the protocol and is only possible if the mobile host receives a timely indication prior to actual link movement as to which neighboring subnet the mobile host will move. This indication can come in the form of a hint from the link layer or a message at the IP layer from the current access router. The message sent from the current access router is called a Proxy Router Advertisement and it contains the same information as would be obtained from a Router Advertisement message on the new subnet. When this information is available the mobile host or access router can initiate localized routing failure repair prior to the link switch thereby removing any source of lost packets during handover. However because timely indication of movement is not possible on all wireless link layers in particular it is not possible on the popular wireless LAN protocol IEEE 1999e dropped packets may be inevitable during the actual link switch and for a short period thereafter until localized routing failure repair can be accomplished from the new link. Routing failure repair allows packets to continue being routed to the mobile host on the new link while the mobile host is changing the care-of address to home-address mapping at the home agent and if route optimization is in effect any correspondent hosts. Packet delivery is accomplished through a bidirectional tunnel between the old router and the mobile host at its new care-of address. The tunnel header in both directions locates the mobile host using its new care-of address. Packets destined for the mobile host arriving at the old router are tunneled to the mobile host. Packets from the mobile host destined to the correspondent are tunneled to the old router. The tunnel is maintained until the mobile host has finished changing the global routing at which point the home agent and correspondent hosts are delivering packets directly to the new care-of .

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