In classic Ethernet terminology, what do the designations 10Base2, 10Base5, and 10BaseT refer to in a local area network?

Introduction / Context:
Ethernet has evolved through many physical layer variants over time. Early standards used coaxial cable and had names like 10Base2 and 10Base5, while later standards used twisted pair and names like 10BaseT. Understanding what these designations mean helps you interpret legacy documentation and exam questions about physical layer characteristics of Ethernet local area networks.

Given Data / Assumptions:

- The question references 10Base2, 10Base5, and 10BaseT specifically.- These names follow a pattern: speed, signaling type, and medium or maximum length code.- We are dealing with Ethernet local area network standards.

Concept / Approach:
Ethernet naming conventions like 10Base2 can be decoded as follows. The number 10 indicates a nominal data rate of 10 megabits per second. The word Base stands for baseband signaling, meaning the entire bandwidth of the medium is used for one digital signal at a time. The suffix indicates the medium type or maximum segment length. In 10Base2 and 10Base5, the numbers roughly refer to maximum segment lengths of about 200 and 500 meters for coaxial cable. In 10BaseT, the T stands for twisted pair copper cabling. All of these designations therefore describe different physical layer implementations of 10 Mbps baseband Ethernet, each with its own cabling and layout rules.

Step-by-Step Solution:
Step 1: Recognise that 10Base2, 10Base5, and 10BaseT are names used in IEEE 802.3 Ethernet standards.Step 2: Decode the prefix 10, which represents 10 megabits per second data rate for each of these standards.Step 3: Interpret the Base part as baseband signaling, meaning digital signaling over the medium without frequency division for multiple channels.Step 4: Interpret the suffix. In 10Base2 and 10Base5, the numerals relate to approximate maximum segment lengths in hundreds of meters using coaxial cable. In 10BaseT, the T indicates twisted pair cabling arranged in a star topology.Step 5: Option A states that these are different 10 Mbps baseband Ethernet physical layer standards specifying cable type and maximum segment length, which matches this interpretation.Step 6: Options B, C, D, and E assign these designations to routing protocols, application services, security levels, or IP address classes, none of which fits the known Ethernet naming scheme.

Verification / Alternative check:
Reviewing summaries of Ethernet standards shows that 10Base5 refers to thick coaxial cable with a maximum segment length of about 500 meters, 10Base2 refers to thin coaxial cable with segments around 200 meters, and 10BaseT refers to twisted pair cabling using star topology with a hub or switch. All operate at 10 Mbps baseband and are part of the physical layer specification in IEEE 802.3. This matches the description in option A exactly and contradicts the alternative options.

Why Other Options Are Wrong:
Option B talks about network layer routing protocols, which have names like RIP, OSPF, and BGP, not 10Base2. Option C refers to application layer services such as HTTP and FTP, which are not named with 10Base codes. Option D supposes that these codes represent encryption levels, which is not part of the Ethernet 10Base naming scheme. Option E suggests that they are IP address classes, but IP classes are written as ranges or prefixes, not as 10Base style strings.

Common Pitfalls:
Students sometimes remember that 10Base2 and 10Base5 have something to do with coaxial cable but forget the meaning of each part of the name. Another common mistake is to confuse these physical layer standards with higher layer protocols that operate over them. To avoid this confusion, always associate 10BaseX names with physical media and line speeds rather than with routing or application functions.

Final Answer:
10Base2, 10Base5, and 10BaseT are different 10 Mbps baseband Ethernet physical layer standards that define the cable type and maximum segment length, as in option A.