The network issues appeared immediately after the cabling was replaced, strongly indicating a problem at the physical layer (OSI Layer 1).

D: If the original installation used Shielded Twisted-Pair (STP) cabling to mitigate high electromagnetic interference (EMI) common in data centers, replacing it with Unshielded Twisted-Pair (UTP) would expose the new cabling to interference. This would lead to signal degradation, packet loss, and intermittent connectivity issues.

E: Transceivers (e.g., SFP, SFP+, QSFP) must match the cable type (e.g., multi-mode vs. single-mode fiber) and the network equipment's port specifications. Using an incorrect transceiver will cause a link to fail to establish or to operate with high error rates, directly causing network issues.

A. The switches are not the correct voltage.

This is a power issue, not a cabling issue. An incorrect voltage would likely prevent the switches from powering on at all, a more severe failure than "network issues."

B. The HVAC system was not verified as fully functional after the fire.

This is an environmental issue. While overheating can cause network problems, it is not a direct consequence of the cabling replacement itself, which is the specified change.

C. The VLAN database was not deleted before the equipment was brought back online.

This is a Layer 2 configuration issue on a switch. It is unrelated to the physical replacement of cables and would not be caused by that action.

F. The new RJ45 cables are a higher category than the old ones.

Higher-category cabling (e.g., Cat6a replacing Cat5e) is backward-compatible and offers better performance. This would be an upgrade and is not a cause of network issues.

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1. On Shielded vs. Unshielded Cabling:

Stallings

W. (2014). Data and Computer Communications (10th ed.). Pearson Education. In Chapter 4

"Transmission Media

" the text explains that "shielded twisted pair (STP) provides better performance at lower data rates" and is used in environments with high interference

such as "near sources of strong electromagnetic interference." Replacing required STP with UTP would introduce noise and errors. (Section 4.1

Twisted Pair).

2. On Transceiver Incompatibility:

Cisco. (2023). Cisco Optics-to-Device Compatibility Matrix. This official vendor documentation provides an extensive list of compatible transceivers for Cisco devices. The existence and detail of this matrix underscore the strict requirement for matching the correct transceiver model to the device and media type. Using an incompatible module (e.g.

single-mode transceiver with multi-mode fiber) will result in a non-functional link. (Document available on Cisco.com

specific part numbers and compatibility are listed throughout the matrix).

3. On Cable Category Backward Compatibility:

Valdivia

P. (2015). Network Engineering. ECE 158A

Winter 2015 Course Notes. University of California

San Diego (UCSD) Department of Electrical and Computer Engineering. Lecture 2

"Physical Layer

" notes that cabling standards like TIA/EIA-568 ensure that higher category cables (e.g.

Cat 6) meet all specifications of lower categories (e.g.

Cat 5e)

making them backward compatible. (Page 15-17).