宋遼兩國建立起長期的和平外交關係之後，經常互相派遣使節進行交聘的活動，如以宋國來說，其中正旦使、生辰使的使遼時間與季節，往往是比較固定在冬季的月份。但是約有四個原因，一是遼承天太后生辰未改期受賀；二是遼帝后死亡與新君登位；三是宋帝死亡與新君登位；四是宋派遣泛使，會造成宋使節有可能在春、夏、秋、冬四季的任何月份使遼。而其所造成的影響，如僅就宋使節來說，則會導致他們晉見遼皇帝的地點、往返的行程路線，以及在遼境中的所見、所聞、所感均不相同。

After the two states of the Song and the Liao established the long term peaceful diplomatic relations, they sent envoys to each other to engage in exchange activities. As to the Song state, the timing and season for the envoys to the Liao state, the Zhengdanshi and the Shengchenshi, were often relatively fixed in the dry, winter months. But there were four reasons for the Song's envoys to the Liao country possibly in any month of the four seasons. Firstly, there was no alteration of the celebration date for the birthday of the Liao's Empress Dowager Chengtian. Secondly, there was the death of the Liao's emperor and empress, and the ascendancy of the new emperor to the throne. Thirdly, there was the death of the Song's emperor and the ascendancy of the new emperor to the throne. Fourthly, the Song dispatched the Fanshi. Impact was accordingly made. For instance, simply for the Song's envoys, it would decide them where to pay visit to the Liao's emperor, the route of the return journey, as well as being completely different in what would be seen, heard, and felt within the Liao territories.