IP Datagram Format
First Word purpose: info, variable size header & packet.
- Version (4 bits)
- Internet header length (4 bits): units of 32-bit words. Min header is 5 words or 20 bytes.
- Type of service (TOS: 8 bits): Reliability, precedence, delay, and throughput. Not widely supported
- Total length (16 bits): header + data. Units of bytes. Total must be less than 64 kB.