Answers and Explanations

A1:	Answer: D. The transfer rate of the bearer channel is 64Kbps. A, B, C, and E all feature incorrect bearer channel transfer rates.
A2:	Answer: B. The transfer rate for the delta channel is 16Kbps. A, C, D, and E all feature incorrect delta channel transfer rates.
A3:	Answer: B. The E-series specifies telephone network standards. A is incorrect because this is not a valid specification. C is incorrect, as the I-series specifies concepts, terminology, and methods for ISDN. D is incorrect, as the Q-series specifies switching and signaling in ISDN.
A4:	Answer: C. The I-series specifies concepts, terminology, and methods for ISDN. A is incorrect because this is not a valid specification. B is incorrect because the E-series specifies telephone network standards. D is incorrect, as the Q-series specifies switching and signaling in ISDN.
A5:	Answer: D. The Q-series specifies switching and signaling in ISDN. A is incorrect because this is not a valid specification. B is incorrect because the E-series specifies telephone network standards. C is incorrect because the I-series specifies concepts, terminology, and methods for ISDN.
A6:	Answer: B. There are only two bearer channels in BRI. A, C, and D all feature the incorrect number of bearer channels in BRI.
A7:	Answer: D. There are 23 bearer channels in PRI for North America as well as 1 delta channel. A, B, and C all feature the incorrect number of bearer channels.
A8:	Answer: D. The PRI D channel has a 64Kbps transfer rate to handle the larger number of bearer channels. Each bearer channel also has a 64Kbps transfer rate. A, B, C, and E all feature incorrect transfer rates.
A9:	Answer: C. There are 30 bearer channels in Europe for PRI. A, B, and D all feature the incorrect number of bearer channels for Europe.
A10:	Answer: B. This is provided by the D channel in ISDN. A is incorrect because the bearer channel carries data. C and D are not valid ISDN channels.
A11:	Answer: A. The bearer channel carries the bulk of network traffic and data. B is incorrect, as this is provided by the D channel in ISDN. C and D are not valid ISDN channels.
A12:	Answer: A. TE1 designates a router or ISDN telephone as a device having a native ISDN interface. B is incorrect because NT-2 indicates the point at which all ISDN lines at a customer site are aggregated and switched. C is incorrect because NT-1 converts the four-wire BRI signals from an S/T interface into the two-wire signals of a U interface. D is incorrect because TE2 is a device such as a PC or router that requires a TA to adapt communication for BRI signals. E is incorrect, as the TA converts EIA/TIA-232 and other signals into BRI signals.
A13:	Answer: B. NT-2 indicates the point at which all ISDN lines at a customer site are aggregated and switched. A is incorrect because TE1 designates a router or ISDN telephone as a device having a native ISDN interface. C is incorrect, as NT-1 converts the four-wire BRI signals from an S/T interface into the two-wire signals of a U interface. D is incorrect, as TE2 is a device such as a PC or router that requires a TA to adapt communication for BRI signals. E is incorrect because the TA converts EIA/TIA-232 and other signals into BRI signals.
A14:	Answer: C. NT-1 converts the four-wire BRI signals from an S/T interface into the two-wire signals of a U interface. A is incorrect because TE1 designates a router or ISDN telephone as a device having a native ISDN interface. B is incorrect because NT-2 indicates the point at which all ISDN lines at a customer site are aggregated and switched. D is incorrect, as TE2 is a device such as a PC or router that requires a TA to adapt communication for BRI signals. E is incorrect because the TA converts EIA/TIA-232 and other signals into BRI signals.
A15:	Answer: D. TE2 is a device such as a PC or router that requires a TA to adapt communication for BRI signals. A is incorrect because TE1 designates a router or ISDN telephone as a device having a native ISDN interface. B is incorrect because NT-2 indicates the point at which all ISDN lines at a customer site are aggregated and switched. C is incorrect because NT-1 converts the four-wire BRI signals from an S/T interface into the two-wire signals of a U interface.
A16:	Answer: E. The TA converts EIA/TIA-232 and other signals into BRI signals. A is incorrect because TE1 designates a router or ISDN telephone as a device having a native ISDN interface. B is incorrect because NT-2 indicates the point at which all ISDN lines at a customer site are aggregated and switched. C is incorrect, as NT-1 converts the four-wire BRI signals from an S/T interface into the two-wire signals of a U interface. D is incorrect because TE2 is a device such as a PC or router that requires a TA to adapt communication for BRI signals.
A17:	Answer: A. The R reference point refers to the connection between a non–ISDN-compatible device and a terminal adapter. B is incorrect because S refers to the point that connects into the NT-2 or customer-switching device. C is incorrect because the T reference point refers to the outbound connection from the NT-2 to the ISDN network. D is incorrect; this refers to the connection between the NT-1 and ISDN network owned by the telephone company.
A18:	Answer: B. S refers to the point that connects into the NT-2 or customer-switching device. A is incorrect because the R reference point refers to the connection between a non–ISDN-compatible device and a terminal adapter. C is incorrect because the T reference point refers to the outbound connection from the NT-2 to the ISDN network. D is incorrect; this refers to the connection between the NT-1 and ISDN network owned by the telephone company.
A19:	Answer: C. The T reference point refers to the outbound connection from the NT-2 to the ISDN network. A is incorrect because the R reference point refers to the connection between a non–ISDN-compatible device and a terminal adapter. B is incorrect, as S refers to the point that connects into the NT-2 or customer-switching device. D is incorrect; this refers to the connection between the NT-1 and ISDN network owned by the telephone company.
A20:	Answer: D. This reference point refers to the connection between the NT-1 and ISDN network owned by the telephone company. A is incorrect because the R reference point refers to the connection between a non–ISDN-compatible device and a terminal adapter. B is incorrect, as S refers to the point that connects into the NT-2 or customer-switching device. C is incorrect because the T reference point refers to the outbound connection from the NT-2 to the ISDN network.
A21:	Answer: C. The NT-1 is supplied by the end user in the United States and by the provider in Europe. A, B, and D are not correct because they are all end-user devices.
A22:	Answer: D. U indicates that the NT-1 is built in. C is incorrect, as this indicates the NT-1 is not built in. A, B, and E are all incorrect, as they have no bearing on the NT-1.
A23:	Answer: C. This is the service profile identifier (SPID) assigned by the provider. D is incorrect, as the terminal ID is not a designation assigned by the ISDN provider. A and B are not valid ISDN acronyms.
A24:	Answer: D. the correct format to specify a national ISDN-1 switch is isdn switch-type basic-ni1. B is incorrect because this is not the proper syntax. A and C use invalid syntax.
A25:	Answer: C. Setting the switch type requires a router reboot to take effect. A is incorrect, as this is not the most likely problem. B is incorrect because reloading the router configuration does not force the setting to take effect. D is incorrect, as this problem is not indicative of an NVRAM problem.
A26:	Answer: D. The 5ESS switch does not require you to configure the SPID. A and B are incorrect, as these are rarely the proper configurations. Typically, both channels are configured, or neither channel is configured. C is incorrect because this is not valid for this switch type.
A27:	Answer: A. This is the proper syntax to configure the SPID. B is incorrect, as you need to specify spid1 or spid2, for instance. C and D are incorrect because isdn should precede the command.
A28:	Answer: B. An interface setting overrides the global setting. A is incorrect because you can override the global setting at the interface level. C is incorrect because both settings are effective. D is incorrect, as this is a valid configuration.
A29:	Answer: A. The proper syntax is pri-group timeslots 1-24. B is incorrect, as the values are 1–24, not 0–23. C is incorrect because the values are wrong, and the pri-group command precedes the timeslots keyword. D is incorrect because the pri-group command has been left out.
A30:	Answer: C. The dialer list in the configuration references access list 110. Access list 110 causes any HTTP traffic to bring up the ISDN connection. This access list is not used as a packet filter, however; so after the ISDN line is up, all traffic (including non-HTTP traffic) is allowed across the link. A and B are incorrect because the configuration is configured correctly. D is incorrect because SMTP is not a subset of HTTP.
A31:	Answer: C. The proper command is show interfaces bri0. D is incorrect, as this does not show the requested information. A and B are invalid IOS commands.
A32:	Answer: C. The show isdn status command displays Layer 1 status and Layer 2 status information. A, B, and D are all invalid IOS commands.
A33:	Answer: A. The debug isdn q921 command shows Layer 2 information for the D channel. B, C, and D are all invalid IOS commands.
A34:	Answer: C. The debug isdn q931 command is the correct command to view Layer 3 debugging information. A, B, and D are invalid IOS commands.
A35:	Answer: B. The debug ppp authentication command allows you to view authentication protocol information, such as that from CHAP and PAP. D is incorrect, as it does not show the requested information. A and C are not valid IOS commands.
A36:	Answer: A. The dialer list is 4 but is applied as number 40. B, C, and D are incorrect because there is nothing wrong with the remaining configuration. E is incorrect because the configuration is complete.
A37:	Answer: C. The debug ppp negotiation command shows PPP traffic exchanges and negotiation information, including LCP and NCP information. A, B, and D are all invalid IOS commands.
A38:	Answer: A. DDR is ideal for low-volume periodic connections and can help keep costs down when cost is tied to the amount of bandwidth used. B is incorrect because high-volume connections can be better served with a persistent high-bandwidth connection. C is incorrect, as persistent connections don't require DDR. D is incorrect because high-volume persistent connections are not served well by DDR.
A39:	Answer: C. Interesting traffic activates the link, causing it to connect and the traffic to be delivered. A is incorrect because this is not interesting traffic as defined by DDR. B is incorrect because interesting traffic should be delivered, not blocked. D is incorrect because interesting traffic does not necessarily initiate at the router.
A40:	Answer: A. The dialer-list command is used to specify interesting traffic by applying an access list to an interface. C is incorrect, as this is not the appropriate command. B and D are invalid IOS commands.
A41:	Answer: A. You use the dialer-group command to associate a port with a dial list. B, C, and D are all invalid IOS commands.
A42:	Answer: A. To associate a dialer string with a dial list, you use the dialer-map command. B is incorrect because this is not the correct command. C and D are both invalid IOS commands.
A43:	Answers: A, B, and C. You must have a static route, you must have dialer information to call the opposite-side router, and you must specify what interesting traffic will initiate the call. D is incorrect, as dynamic routing protocols can cause issues with dial-on-demand routing. E is incorrect because SPIDs are optional and not all switch types or service providers require them. F is incorrect, as Data-link connection identifiers (DLCIs) are used by frame relay to identify virtual circuits.
A44:	Answer: B. The show ip route command shows the static and dynamic routes on the router. C is incorrect, as this is not the appropriate command. A and D are invalid IOS commands.
A45:	Answer: B. The correct command to display statistics is show dialer interface bri0. C is incorrect because it's an incomplete IOS command. A and D are both invalid IOS commands.
A46:	Answer: B. The debug dialer command displays debugging information for the packets on a dialer interface. A and D are invalid IOS commands. C is incorrect; although this is a valid command, it does not show the requested information.
A47:	Answer: D. You use the shutdown command on the interface to disable it. A, B, and C are all invalid IOS commands.
A48:	Answer: B. The correct syntax is dialer idle-timeout 120. A, C, and D are all invalid IOS commands.
A49:	Answer: B. The value can range from 1 to 255, so 25 is roughly 10%. A is incorrect; 25 is around 10% of the maximum of 255. C is incorrect; the value can range up to 255, not 100. D is incorrect; the value can range up to 255, not 25.
A50:	Answers: A, B, and E. ISDN can be used to transfer not only data, but also voice and video. This makes it an excellent choice for a backup WAN connection. C is incorrect, as signaling occurs only on the delta (D) channel, not the bearer channel (B). D is incorrect, as acknowledgments are a function of Transmission Control Protocol (TCP). Although some of the data being sent may contain acknowledgments, it is not a specific item carried by the B channels.