Client-server paradigm Typical network app has two oplication pieces: client and server pny Client: reque g initiates contact with server Speaks first ■●● o typically requests service from server re o Web: client implemented in browser' e-mail: in mail reader plication Server hysical g provides requested service to client o e.g., Web server sends requested Web page, mail server delivers e-mail 2: Application Layer 72: Application Layer 7 Client-server paradigm Typical network app has two pieces: client and server application transport network data link physical application transport network data link physical Client:  initiates contact with server (“speaks first”)  typically requests service from server,  Web: client implemented in browser; e-mail: in mail reader request reply Server:  provides requested service to client  e.g., Web server sends requested Web page, mail server delivers e-mail