GATE CSE 2012 | Question: 10

Question

The protocol data unit (PDU) for the application layer in the Internet stack is:

• A. Segment
• B. Datagram
• C. Message
• D. Frame

Answer 1

(C) Message is the answer.

For Application, Presentation and Session layers, the PDU is message

For Transport layer, PDU is segment for TCP and datagram for UDP

For Network layer, PDU is packet

For Datalink layer, PDU is frames

For physical layer, PDU is stream of bits

Comments

The answer is Message but I have a doubt. If datagram is related to UDP datagram or IP datagram?

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I think datagram is pdu of network layer and not Transport layer, as read from kurose and ross 6th edition pg 51. Why is it that there are so many upvotes for this answer? Am I missing something??

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The datagram is PDU at the transport layer. When UDP protocol is used at transport layer, a unit is called as a datagram in the connection-less transfer (while a unit is called as a segment in case of TCP).

Packet is the PDU at Network layer.

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@coolsid

The transport layer PDU is the segment or the datagram.

Source: https://en.wikipedia.org/wiki/Protocol_data_unit#OSI_model

Answer 2

PDU for the presentation layer is messages.

PDU for transport layer is segment.

PDU for network layer is packet or datagram.

PDU for datalink layer is frame .

PDU for physical layer are bit streams .

Answer 3

Option-C
In Netwok layer PDU is called as Datagram.

In transport layer ,PDU is called as Segment.

Whereas In the application layer the PDU is called as the Message.

Answer 4

PDU for application layer is message.
 For transport layer is segment.
  For network layer is packet or datagram.
   For datalink layer is frame and for physical layer is bit streams.