Computer Networks - What is Protocol Data Unit?

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What is Protocol Data Unit?

The data unit in the LLC level is called the protocol data unit (PDU). The PDU contains of four fields a destination service access point (DSAP), a source service access point (SSAP), a control field and an information field. DSAP, SSAP are addresses used by the LLC to identify the protocol stacks on the receiving and sending machines that are generating and using the data. The control field specifies whether the PDU frame is a information frame (I - frame) or a supervisory frame (S - frame) or a unnumbered frame (U - frame).

Total Answers and Comments: 3

Last Update: May 23, 2008

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Submitted by: monami85

each layer or the osi model , formats the data that it receives , the package of data moves through the layers is called protocol data unit.

       the protocol dat unit name associated with each layer of the osi model layers thats given below check it out

app layer ---------------- data
pres lay   ----------------- data
sess lay ------------------- data
transpor --------------------segments
nw lay    ---------------------packets
data link----------------------frames
physical---------------------- bits

Above answer was rated as good by the following members:
harish_mcsa

March 21, 2006 02:00:56

Tanveer

RE: What is Protocol Data Unit

A unit of data that is passed down from one layer to another in the OSI model. The PDU contains the message and the protocol/control information from the layer above

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March 30, 2008 00:08:44

reehan10

Member Since: March 2008 Contribution: 2

RE: What is Protocol Data Unit?

Protocol data units or PDUs are the messages passed between entities at a given layer.
PDU header + data

<IMG SRC "/figures/figP9.gif" ALT "Protocol and Service Data Units" ALIGN TEXTTOP>

When the PDU passes over the interface from the layer that constructed it to the layer that merely delivers it (and therefore does not understand its internal structure) it becomes a service data unit to that layer. The addition of addressing and control information (which is called encapsulation) to an SDU to form a PDU for that layer.

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May 23, 2008 10:08:00

monami85

Member Since: May 2008 Contribution: 13

RE: What is Protocol Data Unit?

each layer or the osi model formats the data that it receives the package of data moves through the layers is called protocol data unit.

the protocol dat unit name associated with each layer of the osi model layers thats given below check it out

app layer ---------------- data
pres lay ----------------- data
sess lay ------------------- data
transpor --------------------segments
nw lay ---------------------packets
data link----------------------frames
physical---------------------- bits

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