N10-009 Question 12
Single answerLayer 6 - PresentationA company has migrated a customer-facing web application to a new platform. Users can establish HTTPS sessions successfully, but a subset of customers report that downloaded reports open as unreadable characters or with corrupted symbols. Network connectivity, routing, and TCP performance are normal, and packet captures confirm the files are being delivered completely. The application team suspects the issue is related to how the data is being formatted before delivery. Which OSI layer is MOST directly responsible for this function?
- A
Layer 4 - Transport
- B
Layer 5 - Session
- C
Layer 6 - Presentation
- D
Layer 7 - Application
Show answer and explanation
Correct answer: C
Explanation
The best answer is Layer 6 - Presentation. In the OSI model, the Presentation layer handles syntax and formatting of data, including character encoding, data translation, encryption/decryption, and compression. When files arrive intact but display unreadable characters or corrupted symbols, the problem often involves encoding mismatches, improper serialization, or incorrect data formatting before the content is rendered by the client. This aligns with standard OSI descriptions used in networking education and certification objectives, including CompTIA Network+ coverage of Layer 6 responsibilities. By contrast, Layer 4 would be more relevant if packets were being dropped or sessions were unreliable, and Layer 5 would be more relevant if connections could not be established or maintained. Layer 7 is involved in application services, but the specific function of transforming data into a usable representation is most directly associated with Layer 6.
- A. Incorrect.
Layer 4 - Transport is incorrect. The Transport layer is responsible for end-to-end delivery functions such as segmentation, flow control, error recovery, and TCP/UDP port usage. In this scenario, TCP performance is normal and the files are being delivered completely, so transport is not the primary issue. A common misconception is to blame Transport whenever users experience corrupted data, but if delivery is complete and reliable, the problem is more likely with how the data is represented or transformed.
- B. Incorrect.
Layer 5 - Session is incorrect. The Session layer manages the establishment, maintenance, and termination of communication sessions between systems. Since users can successfully establish HTTPS sessions, there is no indication that session setup or maintenance is the root cause. Candidates may choose this option because the problem occurs during an active user session, but session management does not handle file formatting, character encoding, or translation of data structures.
- C. Correct.
Layer 6 - Presentation is correct. The Presentation layer is responsible for data translation, character encoding, serialization/formatting, encryption/decryption, and compression so that data sent by one system can be properly understood by another. In this scenario, the files are transferred successfully but appear unreadable or contain corrupted symbols, which strongly suggests an issue with data representation or formatting rather than transport or connectivity. This is a classic Presentation-layer problem.
- D. Incorrect.
Layer 7 - Application is incorrect. The Application layer provides network services directly to end-user applications, such as HTTP, SMTP, and DNS interactions. While the web application may be the source of the issue, the specific function described involves how data is formatted and represented for interpretation by the receiving system, which maps most directly to the Presentation layer in the OSI model. A common trap is to select Application because the issue involves a web app, but the symptom points to representation rather than service access.