Yes, even when the round trip delay time between the sender and the receiver is constant and known to the sender, yet a timer would still be necessary in the protocol rdt 3.0.
• The round trip delay time will make the sender know whether the packet or the ACK for the packet is lost or not.
• The timers are used to keep track of time the packet is to be transmitted.
• A timer of constant duration is necessary at the sender to detect the loss for each packet.
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