1. In Figure , the sender sends three packets before it expects an ACK. 如图所示，发送端在预期ACK之前传送三个封包。
2. If you want to reply a message to the "Sender" in person, Please open a new mail and put the sender as the recipient. 如果您想要私下回覆讯息至原发信人时，请重开一新邮件，并将该发信人的邮寄地址放至收件人处后发件。
3. In these cases, ICMP sends the sender a destination unreachable message, which indicates that the datagram could not be forwarded. 在这些案例中，ICMP传送给传送端一个目的地不能到达的讯息，它指示资料元无法转送。
英英解释
n.
1. someone who transmits a message
2. set used to broadcast radio or tv signals
