Transmission Frames
All communication between the local and remote stations is accomplished by the transmission of frames.
The SDLC frame format consists of:
| Item | Description |
|---|---|
| Unique flag sequence (B`01111110') | 1 byte |
| Station link address field | 1 byte |
| Control field | 1 byte |
| Information field | n bytes |
| Frame check sequence | 2 bytes |
| Unique flag sequence (B`01111110') | 1 byte |
Three kinds of SDLC frames exist: information, supervisory, and unnumbered. Information frames transport sequenced user data between the local and remote stations. Supervisory frames carry control parameters relative to the sequenced data transfer. Unnumbered frames transport the controls relative to nonsequenced transfers.