BDS DOCSIS Standards and Protocols 1 — Questions and Answers
Question 1: What does DOCSIS stand for?
- Digital Over-Cable Service Interface Specification
- Data Over Cable Service Interface Specification (Correct answer)
- Direct Optical Cable Service Integration Standard
- Digital Optical Communications Service Interface Standard
Correct answer: Data Over Cable Service Interface Specification
DOCSIS stands for Data Over Cable Service Interface Specification, the standard that enables broadband internet over hybrid fiber-coaxial cable systems.
Question 2: What is the role of the CMTS in a DOCSIS network?
- It manages IP address allocation for end users
- It terminates cable modem connections and bridges them to the IP network (Correct answer)
- It amplifies RF signals in the distribution plant
- It encodes video for downstream transmission
Correct answer: It terminates cable modem connections and bridges them to the IP network
The Cable Modem Termination System (CMTS) communicates with cable modems, manages upstream/downstream channels, and connects the HFC plant to the IP backbone.
Question 3: How many downstream and upstream channels can DOCSIS 3.0 bond?
- 4 downstream / 4 upstream
- 8 downstream / 4 upstream
- Up to 32 downstream / 8 upstream (Correct answer)
- Up to 24 downstream / 24 upstream
Correct answer: Up to 32 downstream / 8 upstream
DOCSIS 3.0 supports channel bonding of up to 32 downstream SC-QAM channels and 8 upstream SC-QAM channels to increase aggregate throughput.
Question 4: What modulation technology does DOCSIS 3.1 introduce for the downstream?
- SC-QAM only
- OFDM (Orthogonal Frequency Division Multiplexing) (Correct answer)
- CDMA
- DMT
Correct answer: OFDM (Orthogonal Frequency Division Multiplexing)
DOCSIS 3.1 introduced OFDM for the downstream, enabling up to 4096-QAM and supporting channel widths up to 192 MHz for dramatically higher throughput.
Question 5: What is the purpose of the DOCSIS ranging process during modem initialization?
- To assign an IP address to the modem
- To adjust the modem's transmit power and timing so its upstream signals arrive correctly at the CMTS (Correct answer)
- To download the modem configuration file
- To scan for available downstream channels
Correct answer: To adjust the modem's transmit power and timing so its upstream signals arrive correctly at the CMTS
Ranging synchronizes the cable modem's upstream timing offset and transmit power level so that multiple modems sharing a channel arrive at the CMTS without collision.
Question 6: What file does a cable modem download during initialization to receive its service configuration?
- firmware.bin
- config.cfg (DOCSIS configuration file via TFTP) (Correct answer)
- startup.xml
- modem.json
Correct answer: config.cfg (DOCSIS configuration file via TFTP)
During initialization, a cable modem downloads a binary DOCSIS configuration file via TFTP that specifies its downstream/upstream service flow parameters, QoS, and feature settings.
BDS DOCSIS Standards and Protocols 1
What does DOCSIS stand for?