1. Which of the following acronyms identifies a voice codec used to encode analog voice signals into a 64-kbps digital data stream?
2. How many DS0 channels are in a DS1 in the United States? Answer: E
3. Which of the following best describes the function of demodulation by a modem?
Answer: D. Modems demodulate an analog signal sent by the phone company. The goal is to re-create the original bits sent by the other modem, so the demodulation function converts the analog signal into the bits that it was intended to represent.
4. Which of the following modem standards do not support 56-kbps speeds downstream? Answer: A, B, C, F, G, and H
5. Which of the following terms best describes features of an ISDN PRI in Europe?
Answer: E. PRIs in Europe are based on E1 circuits, which have 32 DS0 channels. One channel is reserved for framing, and one channel is used for a D channel, leaving 30 B channels.
6. Imagine that you plug an analog phone into an ISDN modem and call a friend at her house, where she uses an analog phone using plain-old telephone service (POTS). At which of the following points in a network will a voice codec be used?
Answer: B and D. Because the ISDN modem sends only digital signals over the local loop, it must convert the analog voice from the phone connected to it into digital voice using a voice codec.
7. What does the letter B stand for in the ISDN term B channel? Answer: A
8. Which of the following DSL standards has a limit of 18,000 feet for the length of the local loop?
9. Imagine a local phone line from a house to a local telco CO. When the customer at that house requests DSL service, what type of device does the telco move the CO end of the local line to?
Answer: A. The CO uses a DSLAM to terminate local loops that use DSL. A DSL router or DSL modem is connected to the local loop at the subscriber (home) location.
10. Which of the following protocols are used by DSL modem and routers for data link layer functions?
Answer: A, B, and C. DSL calls for the use of PPP over ATM (PPPoA) over the DSL part of the network. PPP can extend to the PCs at the home location using PPP over Ethernet (PPPoE).
11. Which of the following protocols is used by cable modems for data link layer functions?
Answer: E. Multimedia Cable Network Services (MCNS) defines a MAC layer that also uses IEEE 802.2 as part of the data link layer.
12. Which of the following protocols are used by a cable modem for the upstream data? Answer: B and E
13. Which of the following remote access technologies uses ATM, Ethernet, and PPP as datalink protocols?
14. Which of the following remote access technologies support specifications that allow both symmetric speeds and asymmetric speeds?
Answer: A and C. ISDN always uses symmetric speeds, and cable modems always use asymmetric speeds.
15. Which of the following remote access technologies, when used to connect to an ISP, is considered to be an "always on" service?
Answer: C and D. Analog modems and ISDN lines must signal or dial to set up a circuit before any data can be passed, whereas DSL and cable modems do not do this.
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