In the TCP or IP protocol suite, what are the typical names of the data units used at different layers (application, transport, internet, and network access)?

Introduction / Context:
In layered network models, each layer has its own terminology for the unit of data that it processes. Understanding these terms helps you read protocol descriptions and troubleshoot communication problems. The TCP or IP protocol suite uses a four or five layer view, which can be mapped to the OSI model. This question checks whether you know the standard names for data units at major layers.

Given Data / Assumptions:

• We are considering the TCP or IP suite with application, transport, internet, and network access layers.
• The physical layer deals with raw bits on the medium.
• Different layers may add or remove headers and trailers to form their respective data units.

Concept / Approach:
At the application layer, the protocol deals with data or messages as supplied by the application. When this data is passed down to the transport layer, it is encapsulated into segments (for TCP) or datagrams (for UDP). The internet layer treats these as packets, adding IP headers that include source and destination IP addresses. At the network access or data link layer, packets are carried inside frames that include hardware addressing and error detection fields. Finally, at the physical layer, frames are converted into a stream of bits and transmitted as electrical, optical, or radio signals.

Step-by-Step Solution:
Step 1: Start at the top. Application layer deals with data or messages, not low level units.Step 2: At the transport layer, recall that TCP uses the term segment, while UDP uses the term datagram.Step 3: At the internet layer, which uses IP, the data unit is commonly called an IP packet.Step 4: At the network access or data link layer, the data unit is a frame, which includes MAC addresses and error checking.Step 5: At the physical layer, all of this information is converted into raw bits on the medium.Step 6: Choose the option that lists data or message, segment or datagram, packet, frame, and bits in this order.

Verification / Alternative check:
Networking textbooks and certification materials often use the phrase data, segment, packet, frame, bits as a mnemonic for moving down the stack. Diagrams show encapsulation where each layer adds its own header to the unit it receives from the layer above. For example, the transport layer adds a TCP header to application data to form a segment, and the IP layer adds an IP header to form a packet. This consistent naming scheme matches the description in the correct option.

Why Other Options Are Wrong:
Option B: Assigns bits to the application layer and frames to the transport layer, which reverses the correct order and does not match standard terminology.Option C: Uses the wrong terms at each layer and confuses segments, packets, and frames.Option D: Suggests that all layers use the term file, which is not accurate; files are operating system level objects, not protocol data units.

Common Pitfalls:
A common mistake is mixing up segments and packets or frames, especially when moving between OSI and TCP or IP terminology. Another pitfall is forgetting that the physical layer deals with bits, not with packets or frames. Remembering the sequence data, segment, packet, frame, bits is a helpful way to keep everything in order.

Final Answer:
The correct answer is Application layer: data or message, Transport layer: segment or datagram, Internet layer: packet, Network access layer: frame, Physical layer: bits.