8. Summary Highlights
This section summarizes some noteworthy highlights about various aspects of the DSO protocol.
8.1. QR Bit and MESSAGE ID
In DSO request messages, the QR bit is 0 and the MESSAGE ID is nonzero.
In DSO response messages, the QR bit is 1 and the MESSAGE ID is nonzero.
In DSO unidirectional messages, the QR bit is 0 and the MESSAGE ID is zero.
The table below illustrates which combinations are legal and how they are interpreted:
| MESSAGE ID zero | MESSAGE ID nonzero | |
|---|---|---|
| QR=0 | DSO unidirectional message | DSO request message |
| QR=1 | Invalid - Fatal Error | DSO response message |
8.2. TLV Usage
The table below indicates, for each of the three TLVs defined in this document, whether they are valid in each of ten different contexts.
The first five contexts are DSO requests or DSO unidirectional messages from client to server, and the corresponding responses from server back to client:
- C-P - Primary TLV, sent in DSO request message, from client to server, with nonzero MESSAGE ID indicating that this request MUST generate response message.
- C-U - Primary TLV, sent in DSO unidirectional message, from client to server, with zero MESSAGE ID indicating that this request MUST NOT generate response message.
- C-A - Additional TLV, optionally added to a DSO request message or DSO unidirectional message from client to server.
- CRP - Response Primary TLV, included in response message sent back to the client (in response to a client "C-P" request with nonzero MESSAGE ID indicating that a response is required) where the DSO-TYPE of the Response TLV matches the DSO-TYPE of the Primary TLV in the request.
- CRA - Response Additional TLV, included in response message sent back to the client (in response to a client "C-P" request with nonzero MESSAGE ID indicating that a response is required) where the DSO-TYPE of the Response TLV does not match the DSO-TYPE of the Primary TLV in the request.
The second five contexts are their counterparts in the opposite direction: DSO requests or DSO unidirectional messages from server to client, and the corresponding responses from client back to server.
- S-P - Primary TLV, sent in DSO request message, from server to client, with nonzero MESSAGE ID indicating that this request MUST generate response message.
- S-U - Primary TLV, sent in DSO unidirectional message, from server to client, with zero MESSAGE ID indicating that this request MUST NOT generate response message.
- S-A - Additional TLV, optionally added to a DSO request message or DSO unidirectional message from server to client.
- SRP - Response Primary TLV, included in response message sent back to the server (in response to a server "S-P" request with nonzero MESSAGE ID indicating that a response is required) where the DSO-TYPE of the Response TLV matches the DSO-TYPE of the Primary TLV in the request.
- SRA - Response Additional TLV, included in response message sent back to the server (in response to a server "S-P" request with nonzero MESSAGE ID indicating that a response is required) where the DSO-TYPE of the Response TLV does not match the DSO-TYPE of the Primary TLV in the request.
| C-P | C-U | C-A | CRP | CRA | S-P | S-U | S-A | SRP | SRA | |
|---|---|---|---|---|---|---|---|---|---|---|
| KeepAlive | X | X | X | |||||||
| RetryDelay | X | X | X | |||||||
| Padding | X | X | X | X |
Note that some of the columns in this table are currently empty. The table provides a template for future TLV definitions to follow. It is recommended that definitions of future TLVs include a similar table summarizing the contexts where the new TLV is valid.