In the next few articles, I'd like to concentrate on IP packets and the information that can be found within the headers of an IP packet. We'll then be in good shape to see how this information relates to packet filter rules and firewalls.
Protocols exist at several levels in a telecommunication connection.
There are hardware telephone protocols. There are protocols between each of several functional layers and the corresponding layers at the other end of a communication. Both end points must recognize and observe a protocol. Protocols are often described in an industry or international standard. The IP header is simply a series of bits which have been grouped into fields of a set size.