"Quality of Service Indicators". GSM Mobile Networks - Quality of Service Survey (July 2002). Portugal: Autoridade Nacional de Comunicações. October 2002. Archived from the original on 2005-11-20. Retrieved October 14, 2011.
icp.pt
"Quality of Service Indicators". GSM Mobile Networks - Quality of Service Survey (July 2002). Portugal: Autoridade Nacional de Comunicações. October 2002. Archived from the original on 2005-11-20. Retrieved October 14, 2011.