Optional Protocol Requirements 对可选协议的规定 ; 协议要求 ; 可选协议要求 ; 可选的协议要求
(Optional — not shown) the ability to optimize flows by including protocol messages on the regular application message flow.
(可选的—未表明)能够通过将协议消息包含在常规应用程序消息流量中来优化流量。
The optional match section of the iptables command specifies the characteristics that a packet should have to match the rule, such as source and destination address, protocol, etc.
iptables 命令的可选 match 部分指定信息包与规则匹配所应具有的特征（如源和目的地地址、协议等）。
Protocol buffers supports optional, required and repeated fields. An example of an address book message definition using protocol buffers would look like this.
Protocol buffers支持可选的，必需的和重复的字段。
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