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Thanks. I found a couple of textbooks used for electrical engineering courses at MIT.

Greetings and salutations! I'm trying to find some good literature about the physics of electrical/fiber circuits. I'd like to know a little bit more about what makes it all work. I feel that digging that deep would help better understand why they behave the way they do and also how to cater them to our network needs.

Thanks for the assistance. It looks like the BER errors were only on the D channel. They're going to dispatch someone today to check their equipment.

We have limited responsibility for the length of the circuit. In the photo I attached we are only responsible for the C/DSUs. The circuit run and other hardware belongs to different groups. Our equipment was checked and replaced but the issue persisted.

I wasn't told what the exact errors were. I kept hearing them say they were "locked out of the D-channel" and that's where the errors are. Yesterday a couple of the groups worked together and proved the circuit run, both copper and fiber, tested good. It looks like the issue is with the equipment in the PBX but we keep getting pushback from that group. People here have trouble admitting their stuff is malfunctioning. They act as if it's a slight on themselves.

If this doesn't go here, I apologize. I didn't see a spot for general networking topics.

We have some antiquated equipment where I work. This is the second time that errors were accumulating on a circuit, but not impeding data flow. The errors are on the D-channel of the T1. I know this is a control channel so it doesn't have much of an effect on how data flows. We're being told it is coming from our equipment, which is a GDC 701 CSU/DSU. To me, if it's an issue with the control frame that it would have possibly come from a software configuration issue or possibly the channel bank. I don't believe that errors from our equipment would strictly effect  the D-Channel alone but I can't be 100% sure.

Does anyone here know more about the issues caused by a T1 D-Channel?

Hello CiscoWizard, glad to have you here. Is this the R&S CCNA renewal you're doing?

Yes. I'm pretty much all set to take it. I just need to book the appointment.

Greetings and salutations. My name's John. I'm a CCNA in New York City. I've been a network engineer for about fifteen years. I'm currently preparing to renew my CCNA with the updated exam topics. I'm feeling confident about it so within the next month or two I plan on attempting the exam. After that my goal is to go for the CCNP/CCIE Enterprise certification. I don't know if I'll stop there though. I have an interest in getting security certs and possibly the CCDE. I've also considered the CCIE Service Provider cert. I'm intrigued by those monstrous routing tables a SP engineer must see on a daily basis.

Besides computers, I'm interested in writing, books, science, history, genealogy, exploring, the occult and supernatural, baseball, films, and music.

Welcome here.

Thanks!

Greetings and salutations. My name's John. I'm a CCNA in New York City. I've been a network engineer for about fifteen years. I'm currently preparing to renew my CCNA with the updated exam topics. I'm feeling confident about it so within the next month or two I plan on attempting the exam. After that my goal is to go for the CCNP/CCIE Enterprise certification. I don't know if I'll stop there though. I have an interest in getting security certs and possibly the CCDE. I've also considered the CCIE Service Provider cert. I'm intrigued by those monstrous routing tables a SP engineer must see on a daily basis.

Besides computers, I'm interested in writing, books, science, history, genealogy, exploring, the occult and supernatural, baseball, films, and music.

In that case there should be a choice E.

E. Access - Distribution - Core - NGFW - NGFW (backup) - Core - Core (backup) - Distrocore Sub-Layer - Distribution - Distroaccess Sub-Layer - Access

What I do like about these questions that I feel can have more than one correct answer (and this isn't the first), it implores me to research the answers further and I come away from it learning a lot more. The way you describe it makes sense of course. If the switches were using layer 2 then the redundant link would be blocking. If they're using layer 3, then it's possible to reach the other device through the Distribution layer switch. They don't give you a lot of details as far as the users' networks.

I see the logic in that but I've seen plenty of networks that create the redundancy at the Distribution Layer to avoid using the Core layer for unnecessary traffic. We have over 50,000 employees in my company. The networks are broken down into multiple locations. In the building where I am located we have two main Core devices that head out to the Internet (and to other company locations), but two Distribution layer devices on each floor which act as a backup for each other. We try to keep traffic between two people on the same floor and other floors out of the Core portion of the network. I know others who used the same setup. I feel like the answer being B or D can be relative. At least we do agree both A and C are wrong. 

I came across this practice question and the answer, which I thought was obvious, was actually incorrect according to the site.

What is the path for traffic sent from one user workstation to another workstation on a separate switch in a three-tier architectural model?
A. Access - Core - Distribution - Access
B. Access - Distribution - Distribution - Access
C. Access - Core - Access
D. Access - Distribution -  Core - Distribution - Access

I chose B as the answer. The correct answer is listed as D. It says the other workstation is on another switch, not another network. Why would you need to bring the Core layer into it? And since Distribution layer switches can also be layer 3 switches, you would definitely not need the Core layer.

What does everyone think?