These services are static, as they are known to the system.
这些服务是静态的，因为它们对系统来说都是已知的。
The exchange of goods or services where no money is paid. Also known as barter.
指不采用货币作为中介的商品或服务的交换。
PTV , also known as network TV, is based on IP protocol television services.
也叫网络电视，是指基于IP协议的电视广播服务。
PTV , also known as network TV, is based on IP protocol television services.
也叫网络电视，是指基于IP协议的电视广播服务。
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