Sequenced Packet Exchange
The Sequenced Packet Exchange ( SPX ) protocol can be compared with the TCP and was mainly used in Novell networks. Just like TCP, it is a connection-oriented network protocol . This means that it ensures that the data packets arrive safely at the recipient . It monitors the data sent and requests confirmation of receipt from the recipient. It checks whether a data packet has successfully reached the recipient and confirms it in this case. Using a checksum, it checks whether the data has arrived undamaged. If the data has not arrived at the recipient or if the data is defective, SPX repeats sending the data packet until the transmission is successful.
The protocol in the OSI model
The protocol in the OSI model (see in comparison the TCP / IP reference model , OSI model ):
| OSI layer | English | classification | TCP / IP layer | classification | IPX / SPX / NCP | |
|---|---|---|---|---|---|---|
| 7th | application | Application | Application- oriented |
application | End to end (multihop) |
NCP |
| 6th | presentation | Presentation | ||||
| 5 | meeting | session | ||||
| 4th | transport | transport | Transport- oriented |
Host to host |
SPX | |
| 3 | Mediation | Network | Internet Protocol | Point to point |
IPX | |
| 2 | Fuse | Data link | network |
Ethernet Token Ring FDDI ARCNET |
||
| 1 | Bit transfer | Physical | ||||
SPX header
| SPX header (Sequenced Packet Exchange) | |||||||||||||||||||||||||||||||
| 0 | 1 | 2 | 3 | 4th | 5 | 6th | 7th | 8th | 9 | 10 | 11 | 12 | 13 | 14th | 15th | 16 | 17th | 18th | 19th | 20th | 21st | 22nd | 23 | 24 | 25th | 26th | 27 | 28 | 29 | 30th | 31 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
|
Connection control (connection management) |
Data stream type (data flow type) |
Source connection ID (Source connection ID) |
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Destination connection ID (connection destination ID) |
Sequence number (sequence number) |
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|
Acknowledgment Number (confirmation number) |
Allocation number (allocation number) |
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Data (data) |
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Description of the fields
Connection control
| value | description |
|---|---|
| 0x10 | End of message. |
| 0x20 | Caution. |
| 0x40 | Confirmation needed. |
| 0x80 | Data packet from the system (Original English: System packet; is used internally as a confirmation packet to confirm whether the session partner is active in an inactive session ). |
Data stream type
| value | description |
|---|---|
| 0xFE | End of connection. This is the last message from this connection. |
| 0xFF | Confirmation of the end of the connection. |
- Source Connection ID
- this field is assigned a unique value by the sender for the duration of the connection. This is used to identify the virtual connection.
- Destination Connection ID
- the ID that the recipient assigns to the connection is entered here. If a computer wants to respond to a packet, it takes over the source connection ID and transfers it as the destination connection ID. In the first package, this value is FFFF.
- Sequence number ID
- this contains the consecutive numbering of the SPX packets. Each time a packet is successfully transmitted, the value increases by 1.
- Acknowledgment number ID
- the sequence number ID of the next packet is entered here to ensure that the recipient has received all previous packets.
- Allocation number
- Number of packages sent but not yet confirmed by the recipient
- Data
- The data packet can be between 0 and 534 bytes . If it is a system package, it contains 0 bytes.
Individual evidence
- ↑ Q177463: The Basics of Reading SPX Traces. Retrieved July 16, 2019 (American English).