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Exam 350-801 topic 1 question 309 discussion

Actual exam question from Cisco's 350-801

Question #: 309
Topic #: 1

Refer to the exhibit. An engineer configures ISDN on a voice gateway. The provider confirms that the PRI is configured with 10 channels the engineer ordered and is working from the provider side, but the engineer cannot get a B-channel to carry voice. The rest of the configuration for the serial interface and voice network is functioning correctly. Which actions must be taken to carry voice?

A. The engineer must activate the controller card on the voice gateway before configuring the device.
B. The engineer used a T1 interface but must use an E1 interface.
C. The pri-group timeslots command must be 0-9 for the 10 channels because all values on a router start with 0.
D. The engineer must manually revert the order of using the channels.

Show Suggested Answer

Suggested Answer: D 🗳️

by Testme1235 at Feb. 25, 2023, 1:31 a.m.

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JC2008

Highly Voted 2 years, 3 months ago

D: is very likely the correct answer. A - is not correct, one cannot enter controller T1 interface if the Controller Card is not activated. B - is very unlikely. There is no indication of T1 vs E1, which normally only use outside of USA. C - is incorrect, the pri-group timeslot 1-10 cannot be 0-9 as "0" is not a valid number on Cisco IOS. D - since this is only fractional T1 circuit 1-10, by default IOS outbound calls are in descending order. All outbound calls will go out from bottom up(B-channel 23 and up) unless you manually configure the isdn busy b-channel XX to direct the IOS router not to sending calls out as a full T1 circuit. Therefore by manually revert the order of using the channels will work in this case. Understanding doing so may create glare but this is beside the point for this question.

upvoted 10 times

sneff91

1 year, 3 months ago

Answer is indeed D. Cisco IOS default is a descending channel order for outbound calls: https://www.cisco.com/c/en/us/td/docs/ios/dial/configuration/guide/15-mt/dia_15_mt_book/dia_cfg_isdn_pri.html "Verify if the outgoing B channel calls are made in ascending or descending order. Cisco IOS default is descending order however, if the switch from the service providers is configured for outgoing calls made in ascending order, the router can be configured to match the switch configuration of the service provider."

upvoted 3 times

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MeowthL

2 years, 3 months ago

i'm agreed with you, the answer is D https://www.cisco.com/en/US/docs/ios/dial/configuration/guide/dia_cfg_isdn_pri_external_docbase_0900e4b1806c752c_4container_external_docbase_0900e4b18216dd1b.html

upvoted 1 times

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G0y0

Most Recent 3 months, 2 weeks ago

A. is incorrect. You could not configure The E1/T1 controller if the type card is not configured. C. does not have sense. D., for me is incorrect. The consumption order of the channels does not define whether if there is or not a b-channel. The command isdn bchan-number-order only define the order of the consumption of those ports, but it should not have any impact in a layer 1 problem. Any time we have an issue where there was some calls failed, a random problem, and it was solved by changing the order; but it does not affected the entire trunk.

upvoted 1 times

G0y0

3 months, 2 weeks ago

In fact, it does not matter the order of consumption, it does not define if a b channel exists or not. B,, believe ir or not, is the correct answer. VWIC1/2/3 all of them support E1/T1. If the carrier has a E1configured and the customer has a T1 configured, is enough reason to do not have b-channels, but yo can have d-channel because d-channel is into Layer 2. Commonly, you must ensure that the framing, line coding, and clock source are configured correctly. And the way that you could have this issue, this is one, that customer configured card type t1 meanwhile in the other side have e1, then you will have problem with framing and line code. So, change card type from t1 to e1, and configure a E1 with the correct framing and linecode. B, is correct. https://www.cisco.com/c/en/us/support/docs/wan/t1-e1-t3-e3/8131-T1-pri.html https://www.cisco.com/c/en/us/support/docs/wan/t1-e1-t3-e3/10205-t1-flchrt-main.html

upvoted 1 times

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decdca7

7 months ago

Selected Answer: D

There is no mention of the service to be E1 Then only option is D

upvoted 1 times

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Komy

1 year, 1 month ago

Selected Answer: D

Answer is D

upvoted 2 times

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Testme1235

2 years, 3 months ago

Selected Answer: B

Option A, "The engineer must activate the controller card on the voice gateway before configuring the device," is not a valid solution to this issue because the controller card is already configured and functional since the voice network and serial interface are working correctly. The issue is related to the incorrect interface type being used, which is causing the B-channel to fail to carry voice. Therefore, activating the controller card will not resolve this particular issue.

upvoted 3 times

G0y0

3 months, 2 weeks ago

Yo are right, if the remote side configured E1 and the local side configured T1, it will have problems with linecode and framing, then you will have d-channel and no b-channels. The customer told to carrier to configure 10 channels, but not which of the 23 ones, or 31 ones, because E1 or T1 was no said to the carrier too. I the carrier set E1 and customer T1, you will have problems with framing and linecode and you will not have any b channel. If customer put 1-10 and the carrier put 11-20, answer D. will not solve the problem. Whether it be one or the another one case, you will have to reconfigure the Controller.

upvoted 1 times

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WeNt48

2 years, 3 months ago

Where in the text you have information it should be E1? linecode is correct for T1, so there is not information to think it could be B. C sounds same bad as B. With the information provided honestly I've no clue to pick up correct answer. There is no information that channels should be used ascending or descending, and from my real life experience that would be my first guess to check out - but does this correct answer? Not sure.

upvoted 1 times

G0y0

3 months, 2 weeks ago

The thing is that it is a Layer 1 problem. and I query you, where in the text you have information that the carrier should set T1? also, you are seeing in the exhibit the configuration that the engineer issued in his side, but it doe snot make that the carrier side has a Ti configured. if this were the assumption, if the carrier has a E1, no problem, you change the config from T1 and E1 and configure the line code (AMI or HDB3) and framing (CRC4 or no-CRC4). Probably it is not common a mistake of the type of the interface, but it is not impossible. So, B does not seem to be wrong

upvoted 1 times

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m4tt30000

2 years, 3 months ago

Are u kiddin us? how you activate the card after configuring the controller? this is reversed

upvoted 2 times

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0n3

1 year, 5 months ago

B is correct. The shown configuration is the usual/default configuration for a E1, but the used card type is a T1. https://www.cisco.com/c/dam/en/us/td/docs/routers/ncs4200/configuration/guide/tdm/tdm-cfg-t1-e1-ncs4200-book.html Check the "Configuring the Controller" section.

upvoted 1 times

sneff91

1 year, 3 months ago

Not true. Per the article you linked yourself: "b8zs—Specifies binary 8-zero substitution (B8ZS) as the linecode type. Valid for T1 controller only. This is the default for T1 lines." The linecode here is using b8zs, which isn't supported on an E1. There's also nothing here to suggest that an E1 is the provided service. E1s also don't support ESF. In that article, it has a typo and says: sf—Specifies Super Frame as the T1 frame type. esf—Specifies Extended Super Frame as the T1 frame type. This is the default for E1. crc4—Specifies CRC4 as the E1 frame type. This is the default for E1. no-crc4—Specifies no CRC4 as the E1 frame type. Obviously esf and crc4 cannot both be the default for E1. It should mean to say that ESF is the default for T1.

upvoted 1 times

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