Attached below are my own personal notes showing all the high altitude sectors between LAX and BOS. (Need to be logged into the Forum to access the attachment). The map shows typical sector configurations during the daytime shift. Note that sectors can be combined. Nightime/overnight shift configurations can be much different, often combining with low altitude sectors/frequencies. You can use the LiveATC search function to see what frequencies are covered for each Center, search using the 3 letter ID (ZLA, ZAB, ZDV, etc).