A browser sends an HTTP request to a web server. Which layer of the TCP/IP model is responsible for adding the source and destination IP addresses?
AApplication layer, because HTTP defines the addresses
BTransport layer, because TCP needs IP addresses to route segments
CInternet layer, because IP is responsible for addressing and routing
DLink layer, because MAC addresses are used for all addressing
The Internet layer is where IP lives. Its job is addressing and routing — it wraps the Transport layer segment in an IP packet containing source and destination IP addresses. The Transport layer handles port numbers (which application), not IP addresses. The Link layer adds MAC addresses for the next hop, not end-to-end IP addresses.
Question 2 Multiple Choice
Why does the TCP/IP model combine the OSI Session, Presentation, and Application layers into a single Application layer?
ATo reduce the total number of layers to four for simplicity
BBecause application protocols like HTTP handle session management and data formatting themselves, making the OSI separation artificial
CBecause the Session and Presentation layers were never implemented by any real protocols
DBecause TCP handles session management at the Transport layer
HTTP manages its own sessions (via cookies and keep-alive), defines its own data format (headers, body encoding), and implements application logic — all within one protocol. The OSI distinction between Session, Presentation, and Application layers rarely corresponds to actual protocol boundaries in practice. TCP/IP's consolidation reflects how real protocols are built, not a simplification for its own sake.
Question 3 True / False
The TCP/IP model requires most applications to use TCP as their transport protocol.
TTrue
FFalse
Answer: False
Despite being named 'TCP/IP,' the model supports both TCP and UDP at the Transport layer. TCP provides reliable, ordered delivery; UDP provides lightweight, low-latency delivery without guarantees. Many important applications use UDP — DNS queries, video streaming, VoIP, and online gaming all benefit from UDP's speed over TCP's overhead. The model does not mandate TCP.
Question 4 True / False
In TCP/IP encapsulation, the Transport and Application layer data passes through intermediate routers unchanged.
TTrue
FFalse
Answer: True
Routers process the Link and Internet layers — they strip the incoming frame, examine the IP destination, and re-wrap in a new frame for the next hop — but the Transport and Application layer data passes through untouched. This is why end-to-end reliability (TCP) and application logic (HTTP) work correctly across a network of routers; only the outermost wrapping changes at each hop.
Question 5 Short Answer
What is encapsulation in the TCP/IP model, and why does it allow each layer to operate independently of the layers above and below it?
Think about your answer, then reveal below.
Model answer: Encapsulation is the process by which each layer wraps the data from the layer above it in its own header before passing it downward. The Application layer produces data; Transport wraps it in a segment with port numbers; Internet wraps that in a packet with IP addresses; Link wraps that in a frame with MAC addresses. Because each layer only inspects and modifies its own header, it does not need to understand the contents from other layers — the Internet layer does not know whether the payload is TCP or UDP, or what application is involved. It simply routes IP packets.
This independence is what makes the layered model powerful. You can change the Link layer technology (swap Ethernet for Wi-Fi) without touching TCP or HTTP. You can use a different application protocol (SMTP instead of HTTP) without changing IP or the physical layer. Each layer has a well-defined interface with its neighbors, and the internals of each layer are hidden from all others.