PART I As of December 31, 2010, our domestic network included 17.5 million installed telephone lines, and  reached virtually all homes and businesses in Taiwan.  International network . Our international transmission infrastructure consists of both submarine cable  and satellite transmission systems, which link our national network directly to 101 telecommunications service  providers in 45 international destinations.  International calls are routed between Taiwan and international destinations through one of our two  international switching centers, one located in Taipei and the other in Kaohsiung. Each center had two time- division multiplexing, or TDM, international gateway switches and one NGN international gateway switch. In  total, we had a trunk capacity of 125,040 channels as of December 31, 2010.  As of December 31, 2010, we have invested in 14 submarine cables, seven of which land in Taiwan. While  the number of submarine cables we invest in has decreased from 16 in 2009, we have increased the capacity of  each of our current submarine cables, increasing our aggregate total capacity from 596 Gbps in 2009 to 774 Gbps  in 2010.  Our mobile services network consists of:  The following table sets forth selected information regarding our mobile networks as of the dates indicated.  43 Mobile Services Network  •  cell sites, which are physical locations equipped with a base station consisting of transmitters,  receivers and other equipment used to communicate through radio channels with customers’ mobile  handsets within the range of a cell;  •  BSC (base station controllers) for GSM or RNC (radio network controller) for 3G, which connect to,  and control , the base station within each cell site;  •  base station controllers, which connect to, and control, the base station within each cell site;  •  cellular switching service centers, which control the base station controllers and the processing and  routing of telephone calls;  •  GGSN (gateway GPRS support nodes), which connect our GPRS network to the internet;  •  SGSN (serving GPRS support nodes), which connect the GPRS network to the base station  controllers; and  •  transmission lines, which link (i) with respect to the GSM or 3G network, the mobile switching  service centers, base station controllers, base stations and the public switched telephone network,  and (ii) with respect to the GPRS network, the base station controllers, the support nodes and the  internet.  As of December 31, 2008 2009 2010 GSM system GSM base stations 9,466  9,384  9,336  Switches 49  49  44  Lines of capacity (in thousands) 8,500  7,700  6,500  Taiwan population coverage 99.9% 99.9% 99.9%