An IEEE 802.3 packet (or more properly, Medium Access Control Frame) consists of eight (8) fields. A packet starts with a Preamble, and ends with a Frame Check Sequence. One of the fields, the Protocol Data Unit, is used to implement the Logical Link Control protocol defined by the IEEE 802.2 Standard. This is illustrated in Figure 2"3. Under the IEEE 802.2 Standard, the Protocol Data Unit field is further divided into additional fields, as illustrated in Figure 2"4.
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Last Field |
| Logical Link |
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| First Field |
Transmitted |
| Control |
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Frame | Pad | Protocol |
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Check | (if | Data | Length | Address | Address | Frame | Preamble |
Sequence | needed) | Unit |
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4 | 2 | 6 | 6 | 1 | 7 | ||
bytes | bytes) | bytes | bytes | bytes | bytes | byte | bytes |
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IEEE 802.3
Medium Access Control Frame
Figure 2%3. IEEE 802.3 Frame and Location of IEEE 802.2 Sublayer
| IEEE 802.2 PROTOCOL DATA UNIT |
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| INFORMATION |
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| DSAP |
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| CONTROL | ADDRESS | ADDRESS |
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| Integral number | 8 bits | 8 bits |
| 8 bits |
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Last Byte |
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Transmitted |
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Figure 2%4. IEEE 802.2 Sublayer Fields
Standard or custom communication protocols between higher layer processes are employed in the Information field of the Protocol Data Unit. For example, Node Manager software communications between a local and remote node is accomplished through a Hewlett"Packard Network Management protocol embedded in the Protocol Data Unit Information field.
Excluding the Preamble and Start Frame Delimiter, a packet must be at least 64 bytes, and can be up to 1518 bytes long.
2%4 General Information