Most television stations in Mexico are operated as repeaters of the networks they broadcast. Translator stations in Mexico are given call signs beginning with XE and XH. Televisa and Azteca maintain two national networks apiece. Televisa's Canal de las Estrellas network includes 128 stations (the most in Mexico), and Azteca's networks have 88 and 91 stations. The stations may insert local advertising. Azteca's stations in larger cities may include local news and a limited amount of regional content; Televisa prefers to use its non-national Gala TV network and Televisa Regional stations as outlets for local production. A number of translators also serve areas with little or no signal in their defined coverage area, known as ('shadow channels'). Most shadow channels air the same programming as their parent station. The northern and central regional network Multimedios Televisión in Monterrey uses the same system to a smaller extent (its XHSAW-TDT is the shadow channel of main station XHAW-TDT in Monterrey), with regional output for local newscasts and advertising on a master schedule.