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Troubleshooting High-Speed Data Service Test Questions and
Answers Graded A+
Which Data over Cable Service Interface
Specification (DOCSIS) layer is used by cable
modem termination system (CMTS) to
differentiate between cable modems? -
ANSWER -The DOCSIS Media Access
Control (MAC) Layer.
What was introduced in Data Over Cable Service
Interface Specification (DOCSIS) 3.0 to allow
enough bandwidth for upstream carriers from
previous DOCSIS versions? - ANSWER -
The option to increase the top frequency of the
upstream to 85MHz.
In a Data Over Cable Service Interface
Specification (DOCSIS) network, why is the data
throughput over the return or upstream path
typically less than the throughput of data over the
forward or downstream path? - ANSWER -
Compared to the downstream path, the narrower
bandwidths and lower orders of modulation used
to transport data over the return path cause the
downstream and upstream data throughput to be
unequal or asymmetrical.
What would be the downstream throughput if two
quadrature amplitude modulation (QAM)
channels with a throughput of 38 megabits per
second (Mbps) were bonded? - ANSWER -
76 Mbps.
What are two features that were added in Data
Over Cable Service Interface Specification
(DOCSIS) 3.1 to extend the viability of hybrid
fiber/coax (HFC) network into the next decade? -
ANSWER -Orthogonal frequency division
multiplexing (OFDM) and low-density parity-
check (LDPC).
How does Internet protocol (IP) multicast differ
from IP broadcast? - ANSWER -IP multicast
traffic is only sent to specific modem addresses
on the network; IP broadcast traffic is sent to all
modems on the network.
Which step in the troubleshooting process
requires a discussion with the customer to gather
more detail about the problem? -
ANSWER -Step 1: Identify the problem.
When analyzing a problem, what can the
technician learn by asking the customer to show
or demonstrate the problem? - ANSWER -
The symptoms of the problem can be viewed,
and any unusual screens or customer entries can
be identified.
When using a digital signal analyzer to
troubleshoot data throughput in the Data Over
Cable Service Interface Specification (DOCSIS)
network, what is the minimum modulation error
ratio (MER) into the cable modem for a 256-
quadrature amplitude modulation (QAM) carrier?
- ANSWER -32 dB or greater.
What layers of the Open Systems
Interconnection (OSI) reference model are
specific to cable networks and are present only
between Data Over Cable Services Interface
Specification (DOCSIS) modems and the cable
modem termination system (CMTS)? -
ANSWER -Layers 1 through 4 (Physical
layer, Data Link Layer, Network Layer, and
Transport Layer) are applied between the
DOCSIS modem and CMTS.
