朝贡
tributary system / tributary mission 制度整体用前者，具体使团用后者

通贡
tributary exchange / regular tributary missions 强调"常态化、制度化"的朝贡往来

互市
border trade / frontier market / mutual trade 边境贸易，明清多指茶马互市等
具体到茶马互市：tea-horse trade / tea-horse exchange