In window flow controlled networks, if a packet is lost the destination has to decide whether to save (cache) subsequent out-of-order packets. Also, the source has to decide whether to send just one packet or to send all packets following it. This leads to four different types of caching schemes. Simulations show, against our immediate intuition, that regardless of whether the destination is caching or not, the source should retransmit only one packet. This paper describes the alternatives to, and provides justification for, schemes used in Digital Network Architecture and ARPAnet TCP.

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