adend to the CATV subscriber. 17.6 TWO-WAY CATV SYSTEMS 5 mHz 200 MHz Upstream Low-band Downstream Superband service guard services Mid-band channels chanels channels voice and voice and AA-QQ Upstream downstream 25 MHz 60 MHz Figure 17.16a CATV spectrum based on Ref. 1, showing additional upstream and downstream services. Note the imbalance between upstream and downstream. (Adapted from Ref. 1.) 600 MHz 200 MHz Upstream Downstream Ch. 7, 8 traffic traffic Figure 17.16b CATV spectrum with equal upstream and downstream bandwidth for other services. Return Trunk Feeder Figure 17.17 Trunk/feeder system layout for two-way operation. (From Ref.1, reprinted with permission.) hand, downstream has 60 MHz set aside for these services. In this day of the Internet, this would be providential, because the majority of the traffic would be downstream. 17.6.1.1 Comments on Figures 17.16a and 17.16b. Large guardbands isolate up- stream from downstream TV and other services: 24 MHz in Figure 17.16a and 25 MHz in COMMUNITY ANTENNA TELEVISION (CABLE TELEVISION) Figure 17.16b. A small guardband was placed in the frequency slot from 170 to 174 MHz to isolate downstream voice and data signals from conventional CATV television signals. We assume that the voice service will be POTS (plain old telephone service) and that both the data and voice will be digital. In another approach, downstream voice, data, and special video are assigned the band 550 MHz to 750 MHz, which is the highest frequency segment portion of this system (Ref. 6). In this case we are dealing with a 750-MHz aggregate system. The optical fiber trunk terminates in a node or hub (see Figure 17.12). This is where the conversion from an optical signal to the standard CATV coaxial cable format occurs. Let a node serve four groupings of cable subscribers, each with a coaxial cable with the necessary wideband amplifiers, line extenders, and taps. Typically, such subscriber groups would consist of 200-500 terminations (TV sets) each. Assume that each termination has upstream s