Reasons for sending a SubscribeEventgroupNegativeAcknowledgment include: 发送SubscribeEventgroupNegativeAcknowledgement的原因包括：
Combination of Service ID, Instance ID, Eventgroup ID, and Major Version is unknown 服务ID，实例ID，事件组ID和主要版本的组合未知
Required TCP-connection was not opened by client 必需的TCP连接未由客户端打
Problems with the references options occurred (wrong values, missing endpoint, or conflicting endpoints) 发生引用选项问题（错误值，缺少端点或冲突端点）
Resource problems at the Server . 服务器的资源问题。
If a SubscribeEventgroup entry referencing two conflicting Endpoint Options (UDP or TCP) is received then a SubscribeEventgroupNack shall be generated. Endpoint options are considered conflicting if they are of the same type but hold different values, like different IP or Port number. 如果收到了引用两个冲突的Endpoint option（UDP或TCP）的SubscribeEventgroup entry，则会生成一个SubscribeEventgroupNack。如果Endpoint options属于相同类型但持有不同的值（如不同的IP或端口号），则认为endpoint option存在冲突。
The SubscribeEventgroupNegativeAcknowledgment entry type shall be used to indicate that SubscribeEventgroup entry was NOT accepted. It shall be always sent instead of a SubscribeEventgroupAck if such an error occurred. SubscribeEventgroupNegativeAcknowledgement entry类型应用于表明SubscribeEventgroup entry不被接受。如果发生此类错误，它应始终被发送，而不是SubscribeEventgroupAck entry。
Service ID, Instance ID, Major Version, Eventgroup ID, Counter, and Reserved shall be the same value as in the subscribe that is being answered. 服务ID，实例ID，主要版本，事件组ID，计数器和保留的值应与正在应答的SubscribeEventgroup Entry中的值相同。
The TTL shall be set to 0x000000. TTL应设置为0x000000。
