Need For protocol architecture There are lots of network applications Building each application from scratch is very time-consuming and challenging What commands should be supported -How to respond to each command? -How to identify the two peer applications? Each computer may run multiple applications -How to identify the two computers? -How to convert the data into bit stream? -How to convert the bit stream into signals? How to detect and handle data loss and data error? The network is not perfect -Etc7 Need For Protocol Architecture • There are lots of network applications • Building each application from scratch is very time-consuming and challenging —What commands should be supported? —How to respond to each command? —How to identify the two peer applications? • Each computer may run multiple applications! —How to identify the two computers? —How to convert the data into bit stream? —How to convert the bit stream into signals? —How to detect and handle data loss and data error? • The network is not perfect! —Etc