ISO 8473
Connectionless Network Protocol
Data PDU
Segmentation Part / Options Part
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CNLP can be used in two different PDU types (data PDU, error-report PDU) with the following structure:
1. A fixed part which is used by both types;
2. an address part, also used by both types;
3. a segmentation part only used by data PDUs;
4. a variable options part;
5. a reason for discard field ony used by errror-report PDUs.
Data Unit ID (2 bytes)
Protocol : ISO 9542 / CLNS ES-IS
PDU Part : CLNP / Segmentation Part
Field : data unit identifier
Length : 2 bytes
Contents : packet sequence number.
Segment Offset (2 bytes)
Protocol : ISO 9542 / CLNS ES-IS
PDU Part : CLNP / Segmentation Part
Field : segment offset
Length : 2 bytes
Contents : this segment's location within the original PDU.
If the original PDU / message had been segmented, the segment offset indicates the offset of the current segment.
Total Length (2 bytes)
Protocol : ISO 9542 / CLNS ES-IS
PDU Part : CLNP / Segmentation Part
Field : total length
Length : 2 bytes
Contents : length of original PDU.
The total length value indicates the length of the original PDU (that had been segmented) including header and data field.
Options (n bytes)
Protocol : ISO 9542 / CLNS ES-IS
PDU Part : Options Part
Field : total length
Length : n Bytes
Contents : optional parameter.
If optional parameter are added, the will be structured as follows:
1. Parameter Code
2. Parameter Length
3. Paramete Value