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Tech FeaturesThe Evolutionary Path ofFixed NetworksMu AnrongFrom the 19th century to thebeginning of the 20th century,the global public switchedtelephone network (PSTN) subscribershave experienced a high speed growthand the fixed voice service is themain contributor to carriers’ revenue.But in recent years, the worldwidePSTN telephone networks have finallyreached a plateau.Data from Gartner (see Fig. 1)indicates that the number of theglobal PSTN subscribers will reachits peak in 2007 at about 1.3 billion,and then register a negative growth.On the other hand, Voice over InternetProtocol (VoIP) service, also knownas IP telephony is moving intomainstream. The consumer VoIPmarket will increase at a compoundgrowth rate of 55 percent while thebusiness VoIP will record phenomenalcompound growth rate of 72 percent.VoIP picks up fast in Europe and NorthAmerica. Broadband Internet accessalso maintains its growth momentum.As growth in broadband access internetand VoIP revenues remain robust, thevoice service is projected to accountfor 48 percent of operator’s fixedservices revenue by 2009, as comparedwith 65 percent in 2003.New modes of competition, crosselasticeffects from mobile and VoIPservices are gradually eroding thePSTN business. Circuit-switchedtechnology is being replaced by morecost-effective packet-based wirelessand Internet technologies, leadingto a lower profit margin of voiceservice and a continuous decrease ofaverage revenue per user (ARPU). The8ZTE TECHNOLOGIES