消費者自產品或服務中所獲得之效用，並不一定會全然決定於產品或服務本身， 有時此效用會隨著使用者的增加而增加，此種因其它消費者亦使用該產品或服務而生效用的 特性，稱為「網路外部性（ Network Externalities ）。 本研究首先整理電腦網路服務之網路外部性之來源，研究發現，電腦網路應用服務為具網外 部性特性之產品，其網路外部性來源至少有品質增強效果、後續服務增強效果、使用成本降 低效果、交通負荷增強效果等四種。此四種效果並非僅受使用者數目的數響，網路服務供應 廠商亦可藉由增加此四種效果的方式，達到加強使用者效用的目的。本研究並以數學模式說 明，由於網路外部性的存在，網路服務供應者應注意到長期利潤與短期利潤之衝突。 最後，本研究並將研究所得結果歸納整理為研究命題，後續研究者可據以進行實證研究，以 驗證本研究之推論。

　　　　　The utility that a user derives from usage the products or services increase if the numbers of other users use them increase is defined as network externalities. There are several possible sources of the network externalities in computer network services. There are quality effect, support service effect, usage cost effect, and traffic effect. The effects is influenced not only by the number of users but also by the network suppliers. The study shows that network suppliers would try their best to satisfy the network users. Because of the network externality, the conflicts exist between long term profit and short term profit of network service supplier. A math model was used to explain the phenomenon. Finally, We propose several propositions for future emperical study: 1. Network externality does exist in computer network service; 2. There are 4 sources of network externality. They are Quality Effect, Service Effect, Usage Cost Effect, and Traffic Effect; 3. Computer network supplier can apply different approach to improve network externality; and 4. There are conflicts between long term profit and short term profit of network service supplier.