Multi-Lingual Environments
You cans speak lots of things (IP, CLNP, IPX, Appletalk, etc.)
Someone hands you a pile of bits. What is it?
- Maybe we were careful -- yeah, right
- Maybe we were lucky -- yeah, right
Conclusion: not enough information in the packet header to differentiate -- need an extra field in the data link header to say what it is
- protocol type: well-known (globally administered) values, one field in header
- SAP (service access point) or socket: locally administered, on for dest, on for source
- Don’t confuse “SAP” with IPX’s Service Advertisement Protocol!