This 200-901 practice question tests your understanding of network fundamentals. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
Which TWO of the following are functions of the transport layer in the OSI model? (Choose two.)
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Segmentation and reassembly of data.
Segmentation and reassembly of data is a core function of the transport layer. The transport layer (e.g., TCP) takes data from the session layer, breaks it into smaller segments (segmentation), assigns sequence numbers, and then reassembles these segments in the correct order at the destination. This allows large data streams to be transmitted efficiently over the network layer, which has a maximum transmission unit (MTU) size.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✓
Segmentation and reassembly of data.
Why this is correct
Transport layer segments data and reassembles it at the destination.
Related concept
Read the scenario before looking for a memorised answer.
✓
Providing reliable data transfer with acknowledgements.
Why this is correct
TCP provides reliability; this is a transport layer service.
Related concept
Read the scenario before looking for a memorised answer.
✗
Adding a trailer for error detection.
Why it's wrong here
This occurs at the data link layer.
✗
Encrypting data for secure transmission.
Why it's wrong here
Encryption is a presentation layer function.
✗
Determining the best path to a destination.
Why it's wrong here
This is a network layer function.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the distinction between transport layer functions (segmentation, reliability) and data link layer functions (error detection via trailer), so candidates mistakenly assign trailer-based error detection to the transport layer instead of the data link layer.
Detailed technical explanation
How to think about this question
TCP segmentation involves adding a TCP header (20-60 bytes) with source/destination ports, sequence numbers, and acknowledgment numbers, enabling reliable, ordered delivery. The transport layer also handles flow control via sliding windows and congestion control (e.g., TCP Reno, CUBIC). In contrast, UDP performs segmentation but without reliability or ordering, making it suitable for real-time applications like VoIP where speed is critical.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Network Fundamentals — This question tests Network Fundamentals — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Segmentation and reassembly of data. — Segmentation and reassembly of data is a core function of the transport layer. The transport layer (e.g., TCP) takes data from the session layer, breaks it into smaller segments (segmentation), assigns sequence numbers, and then reassembles these segments in the correct order at the destination. This allows large data streams to be transmitted efficiently over the network layer, which has a maximum transmission unit (MTU) size.
What should I do if I get this 200-901 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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