Transport Protocol (SATP)¶
Transport Protocol (SATP) resides between Control Protocol (SACP) and Routing Protocol (SARP) and operates with the two data units (Message and Segment). Therefore, he has bi-directional work.
Between Application Layer and Transport Layer of the Network Model, it divides into Segments the outbound Message. While between Transport Layer and Network Layer it assembles multiple inbound Segments into single Message.
Transport Protocol (SATP) is a reliable protocol. It can guarantee delivery of each Segment if source device asked for it. Also it can guarantee the integrity of final Message because Transport Protocol (SATP) knows about the order of each Segment.
Segment structure¶
| Part | Field name | Length (bits) | Description |
|---|---|---|---|
| Header | SACP | 8 | SACP Header part |
| SARP | 16 | SARP Header part | |
| SEG | 1 | Segmentation flag | |
| FIN | 1 | Final segment flag | |
| ACK | 1 | Acknowledgment flag | |
| Reserved | 1 | Must be set to 0x0 | |
| Data length | 4 | Length of Data in bytes | |
| Payload | Data | 0-64 | Maximum is 8 bytes |
| CRC | 16 | Checksum |
SACP (8 bits)¶
These are the Channel and Data Classifier for Control Protocol (SACP).
SARP (16 bits)¶
This is an address information that contains Source and Destination IDs for Routing Protocol (SARP).
SEG (1 bit)¶
This is a Segmentation flag. If the Message is not segmented then SEG=0
otherwise SEG=1.
Note
The service information about Segments Order is located in the first byte
of Data field. Therefore it is followed that the maximum number of
Segments is 256. The first Segment marks as 0x0, the second as
0x1 and the last as 0xFF
FIN (1 bit)¶
It indicates that this Segment is final.
ACK (1 bit)¶
This is an Acknowledgment flag. If ACK=1 then this Segment should be
confirmed by recipient about reception.
Data length (4 bits)¶
This is a length of Payload part in bytes. The Segment can be empty
(without Payload). In this situation when Data length=0x0, SEG=0
and FIN=1 Payload part is not presented in the Segment. The maximum
size of Payload part is 8 bytes.
Data (0-64 bits)¶
This is a Payload data. If SEG=1 the first byte of the data will be used
for Segments Order information and another 7 are available for user.
CRC (16 bits)¶
The 16-bit checksum is used for error-checking of the Header and Payload parts.