| 摘要 |
PROBLEM TO BE SOLVED: To provide a low-speed modem relay system and method capable of saving bandwidth in a packet communication network and efficiently recovering a missing packet. SOLUTION: In this modem relay, the link layer of modem signals is connected to locals at both ends of a call, the kind of a low-speed modem is determined by listening to a V.25 answer tone, and negotiations for optimizing the speed and modulation at the ends of a call are conducted to ensure a connection. During a call time, a signal message composed of call control signals and modem control signals is sent to monitor the progress of a call. Data contained in a preceding packet are added to the payload of a current packet, and it is detected by seeing the sequence numbers of the packets whether there are missing packets or not. When no missing packet resides, the latest data field of a packet is used. When missing packets reside, the current packets are called to the last, and the data field of the missing packet is retrieved.
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