Conceptual Server Algorithm Simple Server Algorithm Create a socket Bind the socket to the port Enter an infinite loop Accept request Process request Reply request Not enough in practice generally
Automatic Repeat ReQuest(ARQ) When the receiver detects errors in a packet, how does it let the transmitter know to re-send the corresponding packet? Systems which automatically request the retransmission of missing packets or packets with errors are called ARQ systems Three common schemes Stop Wait
Automatic repeat request (ARQ) Break large files into packets FILE PKT PKT PKT Check received packets for errors Use a feedback channel to request retransmissions Retransmit packets containing errors acket Receive ACK
Key to practice exercise I. GRAMMAR 1.C 2.A在 hope,Ibet结构后的that-分句中可使用一般现在时表示将来的动作。如: bet it rains tomorrow. 3.B.主句中若有 require, demand, suggest insist order, prefer, propose recommend, request等动词,其后的that分句中应使用be型虚拟式,即动次原形或 should+动词原形