d. This can account for 3- to 20-dB additional noise upstream at the headend where the upstream demodulation of voice and data signals takes place. Fortunately, the signal-to- noise ratio requirements for good performance of data and voice are much less stringent than for video, which compensates to a certain extent for this additional noise. 17.6.2.2 Ingress Noise. This noise source is peculiar to a CATV system. It basically derives from the residence/office YV sets that terminate the system. Parts 15.31 and 15.35 of the FCC Rules and Regulations govern such unintentional radiators. These rules have not been rigidly enforced. One problem is that the 75-S2 impedance match between the coaxial cable and the TV set is poor. Thus not only all radiating devices in the TV set, but other radiating devices nearby in residences and office buildings couple back through the TV set into the CATV system in the upstream direction. This type of noise is predominant in the lower frequencies, that band from 5 to 30 MHz that carries the upstream signals. As frequency increases, ingress noise intensity decreases. Fiber-optic links in HFC configurations can provide considerable isolation. 17.6.2.3 Other Upstream Noise Contributors. The following are additional noise contributors for the upstream path: Relative intensity noise (RIN) contributed by the optical node return path laser(s) Intermodulation distortion contributed by broadband amplifiers and the return path laser(s) Shot noise and receiver noise within the optical detector at the headend Multireflections within the HFC plant Burst noise 17.7 TWO-WAY VOICE AND DATA OVER CATV SYSTEMS BASED ON THE DOCSIS 2.0 SPECIFICATION 17.7.1 General Data over Cable Service Interface Specification (DOCSIS) is a family of specifications that permits CATV systems to have two-way capability: voice, data, and broadcast-type television downstream and data and voice upstream. COMMUNITY ANTENNA TELEVISION (CABLE TELEVISION) Table 17.2 DOCSIS Physical Layer, Upstream and Downstream Parameter Upstrea