Question 1.
A few small ITCertKeys locations use HFC cable to connect to the ITCertKeys 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

Explanation:
Hybrid fiber-coaxial (HFC): A mixed optical-coaxial network in which optical fiber replaces some or all of the traditional trunk portion of the cable network. The HFC architecture is the evolution of an initial cable system and signifies a network that incorporates both optical fiber along with coaxial cable to create a broadband network. By upgrading a cable plant to an HFC architecture, you can deploy a data network over an HFC system to offer high-speed Internet services and you can serve more subscribers. The cable network is segmented into smaller service areas in which fewer amplifiers are cascaded after each optical node-typically five or fewer. The tree-and-branch network architecture for HFC can be a fiber backbone, cable area network, superdistribution, fiber to the feeder, or a ring. 

Downstream: An RF signal transmission (TV channels, data) from source (headend) to the destination (subscribers). Downstream is also called a forward path.
Upstream: An RF signal transmission opposite to downstream-from subscribers to the headend. Upstream is also called a return or reverse path.
Delivering services over a cable network requires different RF frequencies-the outgoing frequencies are in the 50-to-860 MHz range, the incoming are in the 5-to-42 MHz range. To deliver data services over a cable network TV channels which usually operate at 6 MHz range for the downstream, and 6 MHz or less (for asymmetric cable connections) for upstream traffic from the corresponding frequency range are usually used.

Question 2.
Many small ITCertKeys 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

Answer: B, C, D

Explanation:
Broadband: Data transmission where multiple pieces of data are sent simultaneously to increase the effective rate of transmission. In cable systems, the term broadband refers to the frequency-division multiplexing (FDM) of many signals in a wide radio frequency (RF) bandwidth over an HFC network, and the capability to handle vast amounts of information. NTSC is a North American TV technical standard for analog TV systems. The standard was created in 1941 and is named after the National Television System Committee formed in 1940. The standard uses a 6-MHz modulated signal. PAL is a color encoding system used in broadcast television systems in most of Europe, Asia, Africa, Australia, Brazil, and Argentina, and uses a 6-MHz, 7-MHz, or 8-MHz modulated signal. The color difference signals an alternate phase at the horizontal line rate. SECAM is an analog color TV system used in France and certain Eastern European countries that uses an 8-MHz modulated signal.

Question 3.
Some of the smaller ITCertKeys locations use HFC cable to connect to the ITCertKeys 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

Explanation:
Hybrid fiber-coaxial (HFC): A mixed optical-coaxial network in which optical fiber replaces some or all of the traditional trunk portion of the cable network. The HFC architecture is the evolution of an initial cable system and signifies a network that incorporates both optical fiber along with coaxial cable to create a broadband network. By upgrading a cable plant to an HFC architecture, you can deploy a data network over an HFC system to offer high-speed Internet services and you can serve more subscribers. The cable network is segmented into smaller service areas in which fewer amplifiers are cascaded after each optical node-typically five or fewer. The tree-and-branch network architecture for HFC can be a fiber backbone, cable area network, superdistribution, fiber to the feeder, or a ring.

Question 4.
A ITCertKeys 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:
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

Question 5.
A new cable modem was shipped to the home of a ITCertKeys user, where it is being installed for the first time. 

When a DOCSIS 1.1 compliant cable modem first initializes, (boots up) what does it do?

A. Establishes IP connectivity (DHCP).
B. Determines the time of day.
C. Requests a DOCSIS configuration file from a TFTP server.
D. Scan for a downstream channel and the establishment of timing synchronization with the 
    CMTS.
E. None of the above.

Answer: D

Explanation:
According to the DOCSIS (Data-over-Cable Service Interface Specifications) when you first power up a cable modem it starts scanning (starting at a low frequency) for a cable signal. When it 'hears' a cable modem stream it listens for a broadcast (from the service provider) which contains information (ie. frequency) needed to talk back with the head end. It then 'talks back' and if it communicates the right authentication information, it is allowed to proceed.

References: 
Page 225 of the CCNP Self-Study BCRAN (642-821) ISBN: 1-58720-084-8
http://www.cisco.com/en/US/products/hw/cable/ps2217/products_feature_guide_chapter09186a008019b57f.htm

Question 6.
You are building a small network at your home and you intend on connecting your cable modem to a Cisco router.

Which router interface would you connect the modem to?

A. Synchronous serial
B. Asynchronous serial
C. Ethernet
D. auxiliary
E. BRI

Answer: C

Explanation:
In certain environments where a non Cisco Cable Modem (CM) is used, and the CM is only capable of bridging, a Cisco router such as the Cisco 806 can be connected to the Cable Modem via the Ethernet interface. The routing can then be performed by the Cisco router behind the Cable Modem and the Client PC or Customer Premises Equipment (CPE) will be connected to the Cisco router. Network Address Translation (NAT) can  then be configured on the Cisco router.

When the Cisco router is connected behind the Cable Modem the first problem that might be encountered is not obtaining an IP address dynamically on the Cisco router's Ethernet interface. Most Internet Service Providers (ISPs) allow only one host or PC behind the Cable Modem. Some ISPs assign an IP address to the PC based on the host name. Therefore, if you have a Cisco router behind the Cable Modem, then the host name for the router configured using the hostname command should be the same host name given by the ISP.
Example:
 

Question 7.
When a cable modem is being provisioned to operate with a host system for Internet services, which two options must occur before Layer 1 and 2 connectivity can occur? (Choose two)

A. The cable modem must request an IP address and core configuration information from a 
    Dynamic Host Configuration Protocol (DHCP) server.
B. The cable modem powering up must scan and lock on the RF data channel in the downstream 
    path.
C. The modem must request a DOCSIS configuration file from a TFTP server.
D. The cable modem must register with the CMTS.
E. The modem must read specific maintenance messages in the downstream path.

Answer: B, E

Explanation:
According to the DOCSIS (Data-over-Cable Service Interface Specifications) when you first power up a cable modem it starts scanning (starting at a low frequency) for a cable signal. When it 'hears' a cable modem stream it listens for a broadcast (from the service provider) which contains information (ie. frequency) needed to talk back with the head end. It then 'talks back' and if it communicates the right authentication information, it is allowed to proceed. Once these steps are completed, layers 1 and 2 will be operational.

Question 8.
How is cable broadband technology able to transmit downstream and upstream data while at the same time delivering television content?

A. The cable operator uses the VHF hyperband to transmit and receive data signals.
B. The cable operator assigns any available spectrum to data, depending on how its own 
    television spectrum is being used.
C. The cable operator uses specific bandwidths for data signals specified by DOCSIS.
D. The cable operator places its data signals into clean areas where there is no interference from 
    noise or other signals.

Answer: C

Explanation:
Developed by CableLabs and approved by the ITU in March 1998, Data Over Cable Service Interface Specification (DOCSIS) defines interface standards for cable modems and supporting equipment. In a cable TV system, signals from the various channels are each given a 6-MHz slice of the cable's available bandwidth and then sent down the cable to your house. In some systems, coaxial cable is the only medium used for distributing signals.
 

When a cable company offers Internet access over the cable, Internet information can use the same cables because the cable modem system puts downstream data -- data sent from the Internet to an individual computer -- into a 6-MHz channel. On the cable, the data looks just like a TV channel. So Internet downstream data takes up the same amount of cable space as any single channel of programming. Upstream data -- information sent from an individual back to the Internet -- requires even less of the cable's bandwidth, just 2 MHz, since the assumption is that most people download far more information than they upload.

Question 9.
ITCertKeys operates a DSL network. What does the "dsl operating-mode auto" command configure on a Cisco router?

A. It configures a Cisco router to automatically detect the proper modulation method to use when 
    connecting an ATM interface.
B. It configures a Cisco router to automatically detect the proper DSL type (ADSL, IDSL, HDSL, 
    VDSL) to use when connecting an ATM interface.
C. It configures a Cisco router to automatically detect the proper encapsulation method to use 
    when connecting an ATM interface.
D. It configures a Cisco router to automatically detect the proper authentication method to use 
    when connecting an ATM interface.
E. None of the above

Answer: A

Explanation:
dsloperating-mode auto interface configuration command to specify that the router automatically detect the DSL modulation that the service provider is using and set the DSL modulation to match. An incompatible DSL modulation configuration can result in failure to establish a DSL connection to the DSLAM of the service provider
Example:
 

Question 10.
ITCertKeys is a DSL service provider using providing xDSL to its customers. 

Which statement about xDSL implementations is true?

A. All xDSL standards operate in lower frequencies than the POTS system and can therefore 
    coexist on the same media.
B. Other than providing higher data rates, HDSL is identical to ADSL.
C. The ADSL standard operates in higher frequencies than the POTS system and can therefore 
    coexist on the same media.
D. The HDSL standard operates in higher frequencies than the POTS system and can therefore 
    coexist on the same media.
E. All xDSL standards operate in higher frequencies than the POTS system and therefore can 
    coexist on the same media.
F. None of the above.

Answer: C

Explanation:
DSL is not a complete end-to-end solution, but rather a physical layer transmission technology similar to dial, cable, or wireless. DSL connections are deployed in the "last mile" of a local telephone network-the local loop. The connection is set up between a pair of modems on either end of a copper wire extending between the customer premises equipment (CPE) and the DSL access multiplexer (DSLAM). A DSLAM is the device located at the central office (CO) of the provider and concentrates connections from multiple DSL subscribers. The term xDSL covers a number of DSL variations, such as ADSL, high-data-rate DSL (HDSL), Rate Adaptive DSL (RADSL), symmetric DSL (SDSL), ISDN DSL (IDSL), and very-high-data-rate DSL (VDSL). DSL types not using the voice frequencies band allow DSL lines to carry both data and voice signals simultaneously (for example, ADSL and VDSL), while other DSL types occupying the complete frequency range can carry data only (for example, SDSL and IDSL). Data service provided by a DSL connection is always-on. The data rate that DSL service can provide depends upon the distance between the subscriber and the CO. The smaller the distance, the higher data rate can be achieved. If close enough to a CO offering DSL service, the subscriber might be able to receive data at rates of up to 6.1 Mbps out of a theoretical 8.448 Mbps maximum.

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