摘要
本篇論文由兩篇在網路經濟學中不同但重要的議題所組成：一篇是關於搜尋引擎贊助商廣告的拍賣，另一篇則是電信巿場接續費的研究。 消費者與廣告商相同都有可能多重選址，但是少有文獻討論消費者的多重選址行為（利用兩個以上的搜尋引擎進行關鍵字的搜索）。因此，在第一章中，我將點擊率（click-through rate）表示成三部分的組合（與廣告商本身相關的的部分，與廣告欄位相關的部分，以及本文中特有的考慮了消費者多重選址行為後的調整項）並建立一個完全資訊下，二個搜尋引擎的關鍵字拍賣模型，用以推導出在考慮消費者和廣告商的多重選址行為後，參與拍賣的廣告商均衡出價策略，以及廣告商們和搜尋引擎們的均衡利潤。在一般化的次價點擊率加權拍賣（generalized second-price click-weighted auction）下，Nash均衡為：贏家（擁有較高品質分數者）永遠會選擇同時在兩個搜尋引擎進行關鍵字拍賣，最後分配的結果會是按照廣告商們加權後的出價高低來排序。若能將過去文獻中的點擊率改成本文所提及的由三部分組合而成的點擊率，則所有參與關鍵字拍賣的廣告商均可以很簡單的出價，如同以前只在一個搜尋引擎下進行拍賣一樣。因而簡化了廣告商們在考慮消費者也會多重選址時，在二個搜尋引擎下的拍賣策略。 而在第二章中，我特別介紹了在電信巿場，實際上網內通話以及網外通話的傳遞路徑，並建立模型來討論在三種不同的成本差異模型下，廠商們的均衡價格及接續費的決定。第一種成本差異是網內通話以及網外通話社會成本的不同（由於傳遞路徑不同），第二種則是轉接成本（switch cost）的不同（由於電信業者光纖網路建設完整性不同），第三種則是發話及受話成本的不同（由於電信業者得標的頻率不同）。當每個電信業者的成本結構相同時，均衡時所決定的接續費會等於成本基礎下的接續費。然而，若電信業者間的成本結構不同時（轉接成本不同或受話及發話成本不同），均衡時所決定的接續費至少會高於電信業者們中最低的受話成本（terminating cost）。只有在電信業者們網內及網外成本結構不同時（第一種成本差異下），均衡的網外對網內的價格比會高於接續費的加價比率（mark up ratio）。而在其餘的 情況下，均衡的網外對網內的加價比會等於接續費的加價比率。
並列摘要
This thesis consists of two very different but important issues on network economics: one in sponsored search auctions, and the other in telecommunication market. Consumers, like advertisers, may multi-home, but few studies have discussed this particular consumer behavior. Hence, in chapter one, I modify the click-through rate into three parts (the bidder-specific part, the slot-specific part and extit{the adjustment part} for the existence of multi-homing consumers) and set up a complete information model in sponsored search auctions with two search engines to derive the bidders' equilibrium bidding strategies and all the agents' equilibrium profits when they face multi-homing consumers. Under the mechanism of generalized second-price click-weighted auctions , I, applying Nash equilibrium, find that the winning bidders (those who have the higher quality scores) always multi-home (bid on both search engines) and their allocation is assortative. By utilizing the adjusted CTRs mentioned in this paper, all bidders can bid as if there is no multi-homing consumers which simplifies finding equilibrium under the situation when bidders bid on more than one search engine. In chapter two, I introduce the real transmitting process in telecommunication market and then set up a model to discuss the equilibrium under three different kinds of cost differences. The first is different social costs between making an on-net call and making an off-net call, the second is different switch costs (because of different fiber networks), and the third is different originating or terminating costs (since different network operators owns different frequency channel). When operators' cost structures are the same, the equilibrium access charge is equal to the cost-based access charge. However, when operators' cost structures are not the same (cost difference in switch cost and cost difference in originating or terminating cost), the equilibrium access charge is higher than the lower terminating cost. Only when there is cost differences between making an on-net call and making an off-net call, the equilibrium price ratio is higher than the mark up ratio. In other cases, the equilibrium price ratio is the same as its corresponding mark up ratio.