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).

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Mar 6th, 2005
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Tanveer

Mar 21st, 2006

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

reehan10
Profile Answers by reehan10

Mar 30th, 2008

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.

monami85
Profile Answers by monami85

May 23rd, 2008

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

adityawalia9
Profile Answers by adityawalia9

Jun 15th, 2010

LAN uses different ways of communicating. In some ways (like ETHERNET) data link layer is divided into two parts MAC and LLC (Logical Link Control).
At LLC the data is known as Protocol Data Unit. It has 4 fields DSAP, SSAP, Control, Upper data layer.
Its main function is to control the flow and error.