This chapter has covered a great deal of information

• The client/server architecture adopted by Internet applications and seen in its use in HTTP, FTP, SMTP, POP3, and DNS protocols
• The increasingly prevalent P2P architecture and its use in P2P file sharing
• How the socket API can be used to build network applications
• The basics of TCP and UDP socket programming

This chapter also began with a basic definition of protocol, but as the topics in this chapter advanced, much more substanance has been added to that definition

Protocols are a key concept in networking; our study of applications protocols has now given us the opportunity to develop a more intuitive feel for what protocols are all about