Some definitions:

Out-of-Band Data (or expedited data)

In order to communicate, host must speak the same protocol.
Each layer of the OSI Model has it's own protocol.

If you change the protocol at one layer on a host, you must change it on all other hosts.

Let's look at a Physical and Data-Link Layer Protocol.

Ethernet:

 

Details of TCP/IP:

 

IP Addresses

1100 0000 0000 1010 0001 0101 0001 1011

has the hexadecimal representation of

C0 0A 15 1B

and therefore would be written as

192.10.21.27

 

Special Addresses