Final answer:
In STBs and DOCSIS modems, the CMTS assigns data to upstream channels based on channel availability, network load, and QoS requirements. Bandwidth request and allocation involve TDMA, ATDMA, and SCDMA access methods to manage multiple devices sharing the same spectrum. The CMTS orchestrates data transmission schedules with MAP messages to prevent collisions.
Step-by-step explanation:
The assignment of data to upstream channels in both STBs (Set-Top Boxes) and DOCSIS modems (Data Over Cable Service Interface Specification) is a complex process that involves communication protocols and network management, typically performed by the Cable Modem Termination System (CMTS). When a modem needs to send data upstream, it communicates with the CMTS to request bandwidth. The CMTS then assigns an upstream channel based on various factors such as channel availability, network load, and Quality of Service (QoS) requirements. In DOCSIS systems, this process also references the Modulation and Coding Scheme (MCS) which is used to determine the robustness of the signal and thus the data rate based on the quality of the cable plant.
Different types of upstream channel access methods are used including TDMA (Time Division Multiple Access), ATDMA (Advanced Time Division Multiple Access), and SCDMA (Synchronous Code Division Multiple Access), which help in managing how multiple devices share the same spectrum efficiently. DOCSIS modems have to contend for upstream bandwidth and the CMTS uses a MAP message to tell each modem on the network when they can send their data to avoid collisions.