CCNA Network Infrastructure and Connectivity Practice Question
Which TWO statements accurately describe the responsibilities of the OSI model's Transport layer?
⚠ Common exam trap
Cisco often tests the distinction between Transport layer flow control (end-to-end) and Network layer congestion control (path-based), leading candidates to confuse Layer 4 segmentation with Layer 3 routing functions.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
It segments data from the upper layers and manages end-to-end flow control.
The Transport layer (Layer 4) segments data from upper layers and manages end-to-end flow control using mechanisms like TCP's sliding window to prevent overwhelming a slow receiver. Option D is correct because the Transport layer provides either reliable delivery (TCP) or unreliable delivery (UDP) between applications on different hosts, ensuring data reaches the appropriate application via port numbers. Option A is incorrect because logical addressing and routing are functions of the Network layer (Layer 3). Option C is incorrect because converting data into electrical signals is the responsibility of the Physical layer (Layer 1). Option E is incorrect because encapsulating data into frames with MAC addresses is a function of the Data Link layer (Layer 2).
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
It provides logical addressing and routing to determine the best path for data.
Why it's wrong here
This describes the Network layer (Layer 3), whose primary device is the router. The Network layer uses logical addressing, such as IPv4 or IPv6 addresses, to identify hosts across different networks and performs routing to select the best path for packets. While the Transport layer relies on the Network layer to deliver its segments, the Transport layer itself does not perform logical addressing or path determination.
- ✓
It segments data from the upper layers and manages end-to-end flow control.
Why this is correct
The Transport layer is responsible for segmenting data received from upper-layer protocols into smaller, manageable units called segments. TCP, for example, implements end-to-end flow control using a sliding window, which prevents a fast sender from overwhelming a slower receiver by adjusting the amount of data transmitted before requiring an acknowledgment. This explicit segmentation and flow-control management is separate from the delivery-reliability service, though both are Transport-layer duties.
- ✗
It converts data into electrical signals for transmission over the physical medium.
Why it's wrong here
This is a Physical layer (Layer 1) function. The Physical layer takes the frame and converts its bits into electrical, optical, or radio signals for transmission over the actual medium, such as copper cable, fiber, or wireless. It defines the electrical characteristics, timing, and encoding methods, but it has no concept of applications, ports, or data reliability — those are higher-layer concerns.
- ✓
It provides reliable or unreliable delivery of data between applications on different hosts.
Why this is correct
This is the defining role of the Transport layer (Layer 4): it provides end-to-end communication services to applications. The two primary protocols are TCP, which guarantees reliable delivery through sequence numbers, acknowledgments, and retransmissions, and UDP, which offers best-effort, connectionless delivery with no recovery mechanisms. This process-to-process delivery is identified by source and destination port numbers, making it distinct from host-to-host delivery at lower layers.
- ✗
It encapsulates data into frames and adds source and destination MAC addresses.
Why it's wrong here
This describes the Data Link layer (Layer 2), not the Transport layer. At Layer 2, frames are created by encapsulating packets with a header and trailer that include source and destination MAC addresses – the physical addresses of devices on the same local network segment. The Transport layer does not deal with MAC addresses or framing; instead, it works with segments and port numbers to manage application-to-application communication.
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The 200-301 exam frequently reuses these exact scenarios with slightly different constraints.
✓It segments data from the upper layers and manages end-to-end flow control.Correct answer▾
Why this is correct
The Transport layer is responsible for segmenting data received from upper-layer protocols into smaller, manageable units called segments. TCP, for example, implements end-to-end flow control using a sliding window, which prevents a fast sender from overwhelming a slower receiver by adjusting the amount of data transmitted before requiring an acknowledgment. This explicit segmentation and flow-control management is separate from the delivery-reliability service, though both are Transport-layer duties.
✗It provides logical addressing and routing to determine the best path for data.Wrong answer — click to see why▾
Why this is wrong here
Logical addressing and routing are functions of the Network layer (Layer 3), not the Transport layer. The Transport layer is concerned with end-to-end communication and data segmentation, not path determination.
Why candidates choose this
Students often confuse the Transport layer with the Network layer because both deal with end-to-end delivery. However, the Network layer handles logical addressing and routing, while the Transport layer manages the connection between applications.
✗It converts data into electrical signals for transmission over the physical medium.Wrong answer — click to see why▾
Why this is wrong here
Converting data into electrical signals is the function of the Physical layer (Layer 1), which deals with the actual transmission of bits over the physical medium. The Transport layer operates above the Physical layer and does not handle signal conversion.
Why candidates choose this
Students may think that all layers eventually convert data to signals, but this specific conversion is exclusive to the Physical layer. The Transport layer works with segments and does not interact directly with the physical medium.
✗It encapsulates data into frames and adds source and destination MAC addresses.Wrong answer — click to see why▾
Why this is wrong here
Encapsulating data into frames and adding source and destination MAC addresses are functions of the Data Link layer (Layer 2). The Transport layer works with segments and uses port numbers, not MAC addresses.
Why candidates choose this
Students often confuse encapsulation at different layers. The Transport layer adds a header with port numbers, but framing and MAC addressing occur at the Data Link layer. This confusion is common when learning the OSI model.
Analysis generated from the official 200-301blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
Quick reference
OSI Model Reference
| Layer | Name | PDU | Key Protocols / Devices |
|---|---|---|---|
| 7 | Application | Data | HTTP, HTTPS, DNS, SMTP, FTP, SSH |
| 6 | Presentation | Data | TLS / SSL, JPEG, ASCII encoding |
| 5 | Session | Data | NetBIOS, RPC, SIP |
| 4 | Transport | Segment / Datagram | TCP, UDP |
| 3 | Network | Packet | IP, ICMP, OSPF — Routers |
| 2 | Data Link | Frame | Ethernet, Wi-Fi, PPP — Switches, Bridges |
| 1 | Physical | Bits | Cables, NICs, Hubs, Repeaters |
Go deeper
Related to this question
Learn chapter
The OSI Model
Key term
Functions
A function is a reusable block of code that performs a specific task, taking inputs, processing them, and returning a result, helping to organize and automate IT workflows.
Key term
Flow control
Flow control is a technique that manages the rate of data transmission between two devices to prevent a fast sender from overwhelming a slow receiver.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 200-301 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 200-301 exam.