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Question: What is Protocol Data Unit?
Answer: 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). |
| March 03, 2008 00:08:44 |
#2 |
| reehan10 |
Member Since: March 2008 Total Comments: 2 |
RE: What is Protocol Data Unit?
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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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