Cisco 642-825 Free Demo – 1
Posted on | January 26, 2010 | No Comments
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Q5
A new cable modem was shipped to the home of a Exambible 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: 1-587208
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http://www.cisco.com/en/US/products/hw/cable/ps2217/products_feature_guide_chapter09186a008019b57f.html
Q6
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:
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Q7
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.
Q8
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:
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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.
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