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ISO - CLNP
Reference of the protocol: Standard ISO
8473 - Connection Less Network Protocol
PDU structure: fields
| bits 8 _ _ _ _ _ _ 1 |
fixed part |
| octet 1 |
Network Layer Protocol Identifier
The value of this field is set to binary 1000 0001 = 81 H to identify this
Network Layer Protocol as ISO8473. |
| octet 2 |
Length indicator
The Length is indicated by a binary number with a maximum value of 254.
The length indicated is the length in octets of the header. |
| octet 3 |
Version / Protocol Identifier Extension
The value of this field is set to binary 1000 0001 = 81 H which identifies
the standard version 1 of ISO8473. |
| octet 4 |
Lifetime
The PDU Lifetime field is encoded as a binary number representing the
remaining lifetime
of the PDU in units of 500 milliseconds. |
| octet 5, bits 8-6 |
Flags:
SP, MS, E/R |
| octet 5, bits 5-1 |
Type |
| octets 6-7 |
Segment length
The Segment Length field specifies the entire length in octets of the PDU,
including both header and data. |
| octets 8-9 |
Checksum
The checksum is computed on the entire PDU header.
For the Data PDU this includes the segmentation and option part.
For the Error report PDU this includes the reason for discard field as
well. |
| - Octet 5: |
Flags |
| bit 8, SP |
Segmentation Permitted
- 1 = Permitted
- 0 = Not Permitted
|
| bit 7, MS |
More Segments
- 1 = the segmentation has occurred and the last octet of NSDU is not
contained in this PDU
- 0 = the last octet of the PDU is the last octet of NSDU
|
| bit 6, ER |
Error Report
- 1 = used to detemine whether to generate an Error Report PDU if it
is necessary to discard this PDU
- 0 = discard of the Data PDU will not cause the generation of an
Error Report PDU
|
| bits 5-4-3-2-1 |
Type |
designation |
| 1 1 1 0 0 |
DT |
Data TPDU |
| 1 0 0 0 0 |
ER |
Error |
-
The number of parameters that may be contained in the options part is constrained by the length of the option part which is determined by the following formula:
-
Option part Length= PDU Header Length - (length fixed part + length address part + length segmentation part)
|
bits 8 _ _ _ _ _ _ 1 |
option part |
|
octet n+6 |
Parameter Code |
|
octet n+7 |
Parameter Length |
|
octets (n+8)-p |
Parameter Value |
If the SP Flag =1 the segmentation part of the Header shall be present.
|
bits 8 _ _ _ _ _ _ 1 |
segmentation part |
|
octets n-(n+1) |
Data Unit Identifier
The Data Unit Identifier identifies an initial PDU (and hence its derived PDU)
so that a segmented data unit may be correctly reassembled.
|
|
octets (n+2)-(n+3) |
Segment offset
For each derived PDU, the Segment offset specifies the relative position
of the segment contained in the Data Part of the derived PDU with respect to the start
of the Data Part of the initial PDU.
|
|
octets (n+4)-(n+5) |
Total Length
The Total Length field specifies the entire length of the initial PDU in octets,
including the header and data.
|
|
bits 8 _ _ _ _ _ _ 1 |
address part |
|
octet 10 |
Destination Address Length Indicator |
|
octets 11-(m-1) |
Destination Address |
|
octet m |
Source Address Length Indicator |
|
octets (m+1)-(n-1) |
Source Address |
|
bits 8 _ _ _ _ _ _ 1 |
data part |
|
octets (p+1)-z |
data field |
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