| 摘要 |
A Layer 2 Tunneling Protocol (L2TP) receiver performs a receiver initiated recovery algorithm (RIRA) when the number of lost or out-of-order payload packets exceed a predetermined value. In particular, the receiver maintains a number of variables: the "next sequence number expected to be received" (Sr) value, and Snl, whic h stores the value of the currently received "next sent" (Ns) sequence number from the latest received packet. When the value of Snl > Sr + adjustment, the receiver portion res ets the value of Sr to the value of Snl and passes all packets to the upper layer of the protocol stack. The value of the adjustment variable represents the number of packets that may b e dropped or out-of-order at the receiver before the receiver initiates recovery. The receiver also sends (either via piggybacking or a zero-length message) an ACK packet to inform t he sender of the new Sr value at the receiver.
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