, ▁additional ▁channels ▁with ▁more ▁limited ▁distribution ▁are ▁offered ▁as ▁add - ons ▁to ▁the ▁basic ▁packages ▁through ▁separate ▁t iers , ▁which ▁are ▁commonly ▁organized ▁based ▁on ▁the ▁programming ▁format ▁of ▁the ▁channels ▁sold ▁in ▁the ▁tier . ▁A ▁la ▁carte ▁subscription ▁services ▁in ▁the ▁U . S . ▁are ▁primarily ▁limited ▁to ▁pay ▁television ▁( more ▁commonly ▁known ▁as ▁" pre m ium ") ▁channels ▁that ▁are ▁offered ▁as ▁add - ons ▁to ▁any ▁programming ▁package ▁that ▁a ▁customer ▁of ▁a ▁mult ich annel ▁video ▁programming ▁distrib utor ▁( also ▁known ▁as ▁a ▁cable ▁or ▁satellite ▁" system " ▁or ▁" provider ") ▁can ▁sub scribe ▁to ▁for ▁an ▁additional ▁month ly ▁fee . ▁ ▁Broadcast ▁television ▁ ▁The ▁United ▁States ▁has ▁a ▁" de central ized ", ▁market - orient ed ▁television ▁system , ▁particularly ▁in ▁regard ▁to ▁broadcast ▁television . ▁The ▁nation ▁has ▁a ▁national ▁public ▁television ▁service ▁known ▁as ▁the ▁Public ▁Broadcast ing ▁Service ▁( P BS ). ▁Local ▁media ▁mark ets ▁have ▁their ▁own ▁television ▁stations , ▁which ▁may ▁either ▁be ▁affili ated ▁with ▁or ▁owned ▁and ▁operated ▁by ▁a ▁television ▁network . ▁St ations ▁may ▁sign ▁affili ation ▁agre ements ▁with ▁one ▁of ▁the ▁national ▁networks ▁for ▁the ▁local ▁rights ▁to ▁carry ▁their ▁programming ; ▁these ▁contract s ▁can ▁last ▁anywhere ▁from ▁one ▁to ▁ten ▁years , ▁although ▁such ▁agre ements ▁often ▁last ▁on ▁average ▁between ▁four ▁and ▁six ▁years . ▁Ex cept ▁in ▁very ▁small ▁mark ets ▁with ▁a ▁limited ▁number ▁of ▁commercial ▁stations ▁(