Advance DOCSIS 3.1
How many pre-equalizer taps are used in DOCSIS 3.1?
24
Field trials have shown that a DOCSIS 3.1 orthogonal frequency division multiplexing (OFDM) channel is how much more resistant to noise and other impairments than legacy DOCSIS channels?
3 decibels (dB).
How many single carrier 256-QAM carriers must be channel bonded to achieve 1,000 Mbps downstream data rates?
32.
What channel bandwidth is the power level out of a single cable modem termination system (CMTS) RF port based upon?
A 6 MHz bandwidth channel.
What does the term bit loading describe?
A DOCSIS 3.1 feature in which each data packet is loaded with extra bits that determine the profile of the incoming signal.?????
In DOCSIS 3.1 Proactive Network Maintenance (PNM), what interacts with other operational support systems (OSS) servers for key information, such as modem locations?
A PNM server.
In DOCSIS 3.1 Proactive Network Maintenance (PNM), what is accessed by a PNM client to display related management information base (MIB) data?
A PNM server.
What are two denotations where the term channel can apply?
A frequency range and a physical path.
What is defined in DOCSIS 3.1 that strengthens the security of cable modem authentication and secures software download features?
A new certificate public key infrastructure (PKI).
Why is a node+0 hybrid fiber/coax (HFC) network design preferred over a node+6 HFC network design?
A node+0 HFC design has no amplifiers, whereas a node+6 HFC design has amplifiers that add noise and distortion to the amplified signal.
What is the least disruptive migration strategy to DOCSIS 3.1 from a previous DOCSIS version?
Adding an orthogonal frequency division multiplexing (OFDM) channel to the downstream frequency spectrum.
Which elements of a hybrid fiber/coax (HFC) network are most likely to cause a service outage because of component failure or loss of power?
Amplifiers.
What is multiplexing?
An efficient method of sharing a common medium for the transport of signals over-the-air (OTA) or though metallic and fiber-optic cable.
What types of applications are most suitable for time division multiplexing (TDM)?
Applications where the transmitted signal is of a non-continuous duration.
Why are exclusion bands within DOCSIS 3.1 24 MHz orthogonal frequency division multiplexing (OFDM) channels forbidden?
Because the guard bands are 1 MHz and there must be at least 22 MHz or more of contiguous modulated OFDM subcarriers.
When first activating Proactive Network Maintenance (PNM) in your network, what is one approach to avoid being overwhelmed by the number of identified problems?
Build a spreadsheet with thresholds set so that the worst performing portion of the network can be identified and corrected first.
How does frequency division multiplexing (FDM) enable multiple signals to share a common medium?
By assigning each signal a specific frequency and bandwidth, or a channel in TV jargon.
What are the two types of orthogonal frequency division multiplexing (OFDM) pilot subcarriers?
Continuous and scattered pilot subcarriers.
Which type of pilot subcarrier can be identified on a spectrum analyzer screen capture of an orthogonal frequency division multiplexing (OFDM) channel?
Continuous pilot subcarriers.
Because they use different transmission and coding schemes, the DOCSIS 3.1 Physical (PHY) Layer is incompatible with the PHY Layer of previous DOCSIS versions. How does DOCSIS 3.1 comply with the requirement of compatibility with previous DOCSIS versions?
DOCSIS 3.1 has two PHY Layers, one for previous DOCSIS versions and another for DOCSIS 3.1. Both Layers can operate simultaneously or individually.
Why is the upstream vulnerable to impairments created inside every connected customer premises?
Each modem has access to the upstream in which the transmitted signals from modems are transported over a common path.
What is used in orthogonal frequency division multiplexing (OFDM) to transform the serial data stream from the time domain to multiple subcarriers in the frequency domain?
Fast Fourier transform (FFT) algorithms compute the discrete Fourier transform (DFT).
In DOCSIS 3.1, the cable modem termination system (CMTS) can support up to 16 downstream profiles per orthogonal frequency division multiplexing (OFDM) channel, but the modems support only how many profiles per OFDM channel?
Four active profiles plus one inactive spare profile (4 + 1) per OFDM channel.
Where does the DOCSIS 3.1 modem acquire its operating parameters when first powered up or initialized?
From either non-volatile memory or from a valid primary downstream channel.
Where does the DOCSIS 3.1 modem gather its downstream channel parameters from when an orthogonal frequency division multiplexing (OFDM) channel is found?
From the Physical Link Channel (PLC) that is within the OFDM channel.
What is the advantage of the multi-profile capability of DOCSIS 3.1 over legacy single profiles?
In multi-profile systems, the data throughput is optimal for the network conditions.
Why are the highest tiers of high-speed data (HSD) service typically a fraction of the DOCSIS downstream capacity?
In order to confidently provide subscribed tier speeds to all customers.
What benefits were cited by the broadband cable operators that utilized DOCSIS 3.0 Proactive Network Maintenance (PNM) in their networks?
Increased customer satisfaction and reduced operational expenses.
In addition to amplifying the signal, what else does an amplifier do?
It adds a small amount of noise and distortion that doubles each time the number of cascaded amplifiers double.
Why is it of concern if a modem is constantly adjusting its output transmission level?
It could indicate an intermittent condition in the network that needs to be identified and corrected.
Under equal network conditions, what advantage does low-density parity-check (LDPC) forward error correction (FEC) coding have over Reed-Solomon (RS) coding?
LDPC is able to correct errors at orders of modulation that are higher than that of RS coding.
The DOCSIS MAC and Upper Layer Protocols Interface (MULPI) specification extends through which layers of the Open Systems Interconnection (OSI) reference model?
Layer 2 through Layer 7.
When two or more nodes share some downstream and upstream channels, and have others unique to each node, then the nodes are in the same Media Access Control (MAC) Domain by virtue of sharing some channels. What are the channels that are unique to each node in the MAC Domain called?
MAC Domain-Cable Modem-Service Groups (MD-CM-SG).
What were the original downstream channel assignments used on hybrid fiber/coax networks based upon?
Over-the-air TV channel assignments.
Why is the practical data rate of a 256-QAM, 6 MHz wide single carrier channel only about 38 megabits per second (Mbps) when the raw data rate is 42.88 Mbps?
Overhead drops the practical data rate to about 38 Mbps.
What is a characteristic of Profile A, because it is the boot profile, that DOCSIS 3.1 modems first begin receiving when they initialize and register?
Profile A should have relatively low bit loading to ensure that it is received by all modems.
Which multi-profile approach establishes a strict hierarchy among the profiles and is the simplest to implement?
Static profile.
What is the DOCSIS 3.1 data rate capacity when a DOCSIS 3.1 orthogonal frequency division (OFDM) channel is bonded to legacy DOCSIS 3.0 bonded channels?
The DOCSIS 3.1 OFDM channel adds to the capacities of the legacy DOCSIS 3.0 bonded channels.
In modular cable modem termination system (M-CMTS) architecture, what automatically compensates for cable length and ensures that the M-CMTS clients have the same sense of time and frequency?
The DOCSIS Timing Interface (DTI) server.
What does the DOCSIS Media Access Control (MAC) Layer use to instruct the cable modem termination system (CMTS) how to route signals internally?
The MAC Domain-Cable Modem-Service Group (MD-CM-SG).
In order to keep good records, tables are constructed describing what is constructed in the cable modem termination system (CMTS). Which table provides the CMTS enough information to ensure that there are no conflicts in frequency assignment?
The Node Configuration Table.
Which type of cable modem termination system (CMTS) table translates (or maps) a node number with a fiber node name?
The Node Configuration Table.
In the DOCSIS architecture, what performs the back office tasks that provision, configure, and manage cable modem operations?
The Operational Support Systems (OSS).
What must be understood when placing a DOCSIS 3.1 orthogonal frequency division multiplexing (OFDM) physical link channel (PLC) in the downstream spectrum?
The PLC carries essential information and should be placed in a portion of frequency spectrum that has little noise and minimal ingress and interference.
What comprises the measurable energy in an orthogonal frequency division multiplexing (OFDM) channel?
The channel's encompassed frequency spectrum minus the unmodulated spectrum in the internal excluded subcarriers and exclusion bands.
What relationship must be maintained when optimizing cyclic prefix and windowing parameters?
The cyclic prefix sample length must be longer than the window length.????????
In DOCSIS 3.1 Proactive Network Maintenance (PNM), what serves as the device under test (DUT)?
The hybrid fiber/coax (HFC) network.
Where does the modem, operating in DOCSIS 3.1 mode, tune to receive data when the downstream contains an orthogonal frequency division multiplexing (OFDM) channel and single carrier-quadrature amplitude modulation (SC-QAM) channels?
The modem tunes to the OFDM channel and the SC-QAM channels, and receives data on both.
What happens if the cable modem receives two different data carriers at the same time?
The modem will receive the highest powered carrier and reject the other.??????
Why are the frequency assignments in the Frequency Space Diagram based on the nodes?
The nodes are where the most frequency congestion can occur.
What indicates an adaptive equalizer's level of sampling and correction capability?
The number of taps in the delay line.
In order to route data to best serve all customers, what does configuration of the cable modem termination system (CMTS) depend on?
The physical layout of the network.?????
On a PreEqualization Analyzer's tap response, what does a digital tap that is less than 10 dB lower than the main tap indicate?
There is a severe micro-reflection in the upstream.
In order for channels to be in the same bonding group, they must meet which of these criteria?
They must be on the same Media Access Control (MAC) Domain.
What DOCSIS 3.1 feature enables an operator to use the same upstream frequency spectrum for DOCSIS 2.0, 3.0, and 3.1?
Time and frequency division multiplexing (TaFDM).
What was the motivation for the conception of the converged cable access platform (CCAP)?
To combine digital television (DTV) and DOCSIS operations from a common unified platform.
What is the purpose of the cyclic prefix (CP)?
To compensate for micro-reflections in the transmission path by providing a protective interval between successive orthogonal frequency division multiplexing (OFDM) symbols.
What are the responsibilities of the Physical Layer (Layer 1) in the Open Systems Interconnection (OSI) reference model and DOCSIS?
Transmission stream of data bits.
What over-the-top (OTT) delivered content could cause the current broadband network data rates to become inadequate?
Ultra-high definition TV (UHDTV) content
What does DOCSIS 3.1 employ to fully utilize the entire upstream spectrum at maximum capacity while maintaining backward compatibility with DOCSIS 3.0?
Upstream channel bonding and time and frequency division multiplexing (TaFDM).
