In classic Ethernet network design, what does the 5-4-3 rule state about the maximum number of cable segments, repeaters, and populated (user) segments between any two stations on a shared collision domain?

Introduction / Context:
The 5-4-3 rule is a classic design guideline for early shared Ethernet networks using coaxial cable and repeaters, such as 10Base5 and 10Base2. Although modern switched Ethernet does not rely on this rule, it is still an important concept in networking theory and exams. The rule helps ensure that collisions can be detected reliably and that signal timing constraints are respected across a shared collision domain.

Given Data / Assumptions:

• We are discussing traditional shared Ethernet using repeaters, not modern switched Ethernet.
• A single collision domain may span multiple cable segments connected by repeaters.
• The 5-4-3 rule describes limits on segments, repeaters, and populated segments.
• Stations must be able to detect collisions within a defined maximum propagation time.

Concept / Approach:
The 5-4-3 rule says that between any two stations on a shared Ethernet collision domain, you can have a maximum of 5 cable segments connected by 4 repeaters, and among those 5 segments, only 3 may be populated (segments with user stations attached). The remaining 2 segments, if present, must be inter-repeater links with no user devices attached. This limitation keeps the round-trip propagation delay within Ethernet's collision detection window, which is based on the minimum frame size and bit time.

Step-by-Step Solution:
1. Identify what each number in the 5-4-3 rule represents: 5 segments, 4 repeaters, 3 populated segments.2. Understand that a segment is a physical cable run, and a populated segment has user devices attached, while an inter-repeater segment connects only repeaters.3. Realise that the purpose of the limit is to bound the propagation delay so that a transmitting station can still detect a collision anywhere in the domain while transmitting the minimum-size Ethernet frame.4. Compare the options: Option A explicitly states that a shared Ethernet collision domain can have at most 5 segments, 4 repeaters, and 3 populated segments between any two stations, which matches the textbook definition.5. Options B, C, and D describe completely different and incorrect network design rules involving switches, routers, Wi-Fi, or token ring.6. Therefore, Option A correctly explains the 5-4-3 rule.

Verification / Alternative check:
You can verify this by checking classic Ethernet design references, which state that the rule applies to 10 Mbps shared Ethernet with repeaters. Diagram examples show up to 5 segments joined by 4 repeaters, with only 3 segments carrying end stations. Modern switched Ethernet and full-duplex links remove collision domains and thus do not need this rule, which further supports that the 5-4-3 rule is specific to legacy shared media Ethernet.

Why Other Options Are Wrong:
Option B is wrong because it mixes devices like switches, routers, and firewalls and has no connection to the 5-4-3 Ethernet guideline.Option C is wrong because token ring networks use different concepts and do not follow a 5-4-3 rule.Option D is wrong because Wi-Fi design uses channel planning and cell sizing, not the 5-4-3 rule based on repeaters and segments.

Common Pitfalls:
Students sometimes think 5-4-3 is a universal networking rule that applies to all LAN technologies, but it is specific to classic shared Ethernet. Another common mistake is to misinterpret the numbers as counts of hosts or devices rather than segments and repeaters. Remember that only 3 of the 5 segments are allowed to have user stations, and the remaining 2, if present, are inter-repeater links. Understanding these details can help you answer theoretical questions about legacy Ethernet designs.

Final Answer:
A shared Ethernet collision domain can have at most 5 segments, 4 repeaters, and 3 populated (user) segments between any two stations.