Typically, the upstream or ATU C modem transmits {HEAD ~ data} to the downstream or ATU R modem over a first set of subchannels, which are usually the higher frequency subchannels, and receives {TAIL ~ data} from the downstream or ATU R modem over a second, usually smaller, set of subchannels, commonly the lower frequency subchannels 
Typically , the upstream or ATU C modem transmits { HEAD ~ data } to the downstream or ATU R modem over a first set of subchannels , which are usually the higher frequency subchannels , and receives { TAIL ~ data } from the downstream or ATU R modem over a second , usually smaller , set of subchannels , commonly the lower frequency subchannels
OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH