What is the transport layer transmission format for connectionless communication?

N10-009 By islever Editorial Last updated

Short answer

A Datagram

Question

Which of the following best describes the transmission format that occurs at the transport layer over connectionless communication?
  1. Datagram Correct Answer
  2. Segment
  3. Frames
  4. Packets

Key Takeaways

This question tests your ability to distinguish TCP and UDP PDU names at the transport layer: UDP connectionless traffic uses datagrams, while the common trap is selecting 'Segment' because it is often memorized as the general Layer 4 PDU.

In CompTIA Network+ (N10-009), the transport layer uses different PDU names for its two protocols: segments for connection-oriented TCP and datagrams for connectionless UDP. Community consensus strongly favors Datagram, with 64 votes for A versus 36 for B, confirming that the key is the word 'connectionless.'

Common mistake: The most common wrong answer is B, Segment, chosen by candidates who map the transport layer to 'segment' without noticing the keyword 'connectionless'—segments are the PDU for connection-oriented TCP, not for UDP.

Expert Analysis

Why the Answer Is Correct

A connectionless transport-layer protocol is UDP, and the PDU used by UDP is called a datagram. Comment [1] correctly states that a datagram is a connectionless transfer unit created with UDP. Comment [3] reinforces this by noting the keyword 'connectionless' and contrasting TCP segments with UDP datagrams. Therefore, A (Datagram) is the best description for the transmission format at the transport layer over connectionless communication.

Why the Other Options Are Wrong

Option B (Segment) is the PDU for TCP, which is connection-oriented, not connectionless—so it fails because the question explicitly specifies connectionless communication. Option C (Frames) belongs to the data-link layer, and option D (Packets) belongs to the network layer, both lower in the OSI model. Only datagram correctly identifies the transport-layer PDU for UDP.

Community Comment Notes

Comment [4] also supports A, explaining that datagrams are the fundamental units of transmission in connectionless protocols like UDP. Comment [5] lists the common Layer 4 = Segment rule but misses the protocol distinction; this is the typical source of the B vote. Comment [2] uses a mnemonic ('Stop - Segments' etc.) but still lands on datagram for Layer 4? Actually the mnemonic lists Layer 4 as segments, showing why many choose B—the caveat is connectionless versus connection-oriented.

Official Reference

These links open the official vendor documentation in a new tab.

Exam Strategy

Underline qualifiers like 'connectionless' and 'connection-oriented' before selecting a PDU name. Remember the simple pairing: TCP = segment, UDP = datagram, IP = packet, Ethernet = frame, and always let the protocol type override generic OSI-layer memorization.

Community Votes

A
64%
B
36%

64% of anonymous learners picked answer A. Votes are pick records left by other test-takers — they are not the verified answer.

Discussion 6 contributions

Compiled from public community threads and reader submissions, lightly edited for clarity. Handles and vote tallies are shown as recorded, and comments reflect the views of individual contributors.

From public community threads 6

  1. HeatSquad77 👍 5 Answered A
    A. Datagram A connectionless transfer unit created with User Datagram Protocol designed for quick transfers over a packet-switched network
  2. AriGarcia 👍 3 Answered B
    7) Dont - Datagram 6) Dont - Datagram 5) Dont - Datagram 4) Stop - Segments ==> Answer 3) Pouring - Packets 2) Free - Frames 1) Beer - Bits
  3. 93831b0 👍 2 Answered A
    A. Datagrams are used in connectionless communication protocols like TCP and UDP at the transport layer. Datagrams are fundamental units of transmission, representing segments of data for error detection and retransmission.
  4. fc040c7 👍 2 Answered A
    “Connectionless” is the keyword. I first skipped right over that ajd said segments as well. TCP - segments UDP - user DATAGRAM protocol….
  5. Philco 👍 1 Answered B
    I tend to disagree with this the answer as: A. Datagram Layer 1 = Bits = Physical Layer 2 = Frames = Data Layer 3 = Packet = Network Layer 4 = Segment = Transport Layer 5 = Data Exchange = Session Can somebody either Confirm this or Correct me please?
Show 1 more comment
  1. CalicoJack 👍 1 Answered B
    Layer 4 = Segment = Transport

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