Inside Macintosh: Networking With Open Transport / Part 2 - Open Transport Reference

Chapter 28 - Advanced Topics Reference / Constants and Data Types

OTData Constant

When sending data that is noncontiguous, you need to use an OTData buffer. Open Transport provides a constant, kNetbufDataIsOTData, that you can use for the TNetbuf.len field when you send data to indicate that the value in the TNetbuf.buf structure is actually a pointer to an OTData buffer.

enum {
   kNetbufDataIsOTData= 0xfffffffe
};