Message Provided to Transport Layer
| User Data |
Transport Layer
| TCP Header | User Data |
Network Layer
| IP Header | TCP Header | User Data |
or
| PPP | TCP Header | User Data | PPP |
Transmission Control Protocol (TCP) Header Format
| bit | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 |
| Byte 0 Byte 1 |
Source Port Number | |||||||
| Byte 2 Byte 3 |
Destination Port Number | |||||||
| Byte 4 Byte 5 Byte 6 Byte 7 |
Sequence Number | |||||||
| Byte 8 Byte 9 Byte 10 Byte 11 |
Acknowledgement Number | |||||||
| Byte 12 | Header Length | |||||||
| Byte 13 | URG | ACK | PSH | RST | SYN | FIN | ||
| Byte 14 Byte 15 |
Window Size | |||||||
| Byte 16 Byte 17 |
TCP Checksum | |||||||
| Byte 18 Byte 19 |
Urgent Pointer | |||||||
Internet Protocol (IP) Header Format
| bit | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 |
| Byte 0 | Version Indicator | Header Length Indicator | ||||||
| Byte 1 | Type of Service(TOS) | |||||||
| Byte 2 Byte 3 |
Total Length (in bytes) | |||||||
| Byte 4 Byte 5 |
Identification | |||||||
| Byte 6 | Flags | Fragment Offset | ||||||
| Byte 7 | Fragment Offset | |||||||
| Byte 8 | Time To Live (TTL) | |||||||
| Byte 9 | Protocol | |||||||
| Byte 10 Byte 11 |
Header Checksum | |||||||
| Byte 12 Byte 13 Byte 14 Byte 15 |
Source IP Address | |||||||
| Byte 16 Byte 17 Byte 18 Byte 19 |
Destination IP Address | |||||||
PPP (Point-to-Pont Protocol) Frame Format
| bit | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 |
| Byte 0 | Flag(=01111110) | |||||||
| Byte 1 | Address (=11111111) | |||||||
| Byte 2 | Control(=00000011 usually) | |||||||
| Byte 3 | Protocol Identifier | |||||||
| Data/Payload (padded up to 1,500 bytes usually) | ||||||||
| Byte 4 Byte 5 |
Checksum (can be two or four bytes) | |||||||
| Byte 6 | Flag(=01111110) | |||||||
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© 1997 by STM&P, Inc.
Updated 2/1/98 by CAR