In this illustration, we see the outline of a building labeled "Cable head end" (which contains the CMTS) on the left, and a neighborhood of houses labeled "Residences with cable modems" on the right. Between them are two blue arrows-one extends from the cable head end to the residences, and is labeled "Downstream channel i." The other extends from the residences to the cable head end, and is labeled "Upstream channel j." Above the arrows is a white box labeled "MAP frame for interval [t1,t2]." A smaller blue arrow points from this box to the residences. Below the arrows is a dotted line that extends between the cable head end and the residences. The left end of the line is labeled t1 and the right side is labeled t2. The first third of this line, from left to right, is labeled "Minislots containing minislot request frames," and the last two-thirds of the line is labeled "Assigned minislots containing cable modem upstream data frames."