Topic 1, Implement Basic Teleworker Services (37

Questions)

Section 1: Describe Cable (HFC) technologies (8 Questions)

Q1
A few small  Exambible locations use HFC cable to connect to the Exambible WAN.
Which HFC cable network statement is true about the downstream data channel to the customer and the upstream data channel to the service provider?

A. The upstream data path is assigned a channel in a higher frequency range than the downstream path has.
B. The downstream data path is assigned a 30 MHz channel and the upstream data path is assigned a 1 MHz channel.
C. The downstream data path is assigned a fixed bandwidth channel and the upstream data path uses a variable bandwidth channel.
D. Both upstream and downstream data paths are assigned in 6 MHz channels.
E. None of the above.

Answer: D

Q2
Many small Exambible branch offices use broadband cable for data connection access. Which three modulation signaling standards are used in broadband cable technology? (Select three)

A. S-Video
B. NTSC
C. SECAM
D. PAL
E. FEC
F. FDM
G. MLP

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Answer: B, C, D

Q3
Some of the smaller Exambible locations use HFC cable to connect to the Exambible WAN. Which two statements are true about broadband cable (HFC) systems? (Select two)

A. Cable modems operate at Layers 1, 2, and 3 of the OSI model.
B. Cable modems operate at Layers 1 and 2 of the OSI model.
C. A function of the cable modem termination system is to convert the digital data stream from the end user host into a modulated RF signal for transmission onto the cable system.
D. Cable modems only operate at Layer 1 of the OSI model.
E. A function of the cable modem termination system (CMTS) is to convert the modulated signal from the cable modem into a digital signal.

Answer: B, E

Q4
A Exambible remote user is getting Internet access from the local cable provider.
When an individual is connected to the Internet by way of a CATV cable service, what kind of traffic is considered upstream traffic?

A. Traffic going from the user’s home traveling to the headend.
B. Broadcast traffic, including the cable TV signals.
C. Traffic between the headend and the TV signal.
D. Traffic between the headend and the supplier antenna.
E. Traffic from outside the local cable segment serving the user’s home.
F. All of the above can be considered upstream

Answer: A

Explanation:

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In the CATV space, the downstream channels in a cable plant (cable head-end to subscribers) is a point-to-multipoint channel. This does have very similar characteristics to transmitting over an Ethernet segment where one transmitter is being listened to by many receivers. The major difference is that base-band modulation has been replaced by a more densely modulated RF carrier with very sophisticated adaptive signal processing and forward error correction (FEC).
In the upstream direction (subscriber cable modems transmitting towards the head-end) the environment is many transmitters and one receiver. This introduces the need for precise scheduling of packet transmissions to achieve high utilization and precise power control so as to not overdrive the receiver or other amplifier electronics in the cable system. Since the upstream direction is like a single receiver with many antennas, the channels are much more susceptible to interfering noise products. In the cable industry, we generally call this ingress noise. As ingress noise is an inherent part of CATV plants, the observable impact is an unfortunate rise in the average noise floor in the upstream channel. To overcome this noise jungle, upstream modulation is not as dense as in the downstream and we have to use more effective FEC as used in the downstream.
Reference: http://www.cisco.com/warp/public/759/ipj_1-3/ipj_1-3_catv.html