Most CBC television stations, including those in the major cities, are owned and operated by the CBC itself. CBC O&O stations operate as a mostly seamless national service with few deviations from the main network schedule, although there are some regional differences from time to time. For on-air identification, most CBC stations use the CBC brand rather than their call letters, not identifying themselves specifically until sign-on or sign-off (though some, like Toronto's CBLT, do not ID themselves at all except through PSIP). All CBC O&O stations have a standard call letter naming convention, in that the first two letters are "CB" (an ITU prefix allocated not to Canada, but to Chile) and the last letter is "T". Only the third letter varies from market to market; however, that letter is typically the same as the third letter of the CBC Radio One and CBC Radio 2 stations in the same market. An exception to this rule are the CBC North stations in Yellowknife, Whitehorse and Iqaluit, whose call signs begin with "CF" due to their historic association with the CBC's Frontier Coverage Package prior to the advent of microwave and satellite broadcasting.