Читать книгу Mobile Communications Systems Development - Rajib Taid - Страница 68

Consider the File Transfer Protocol (FTP) that is used to upload and download files between two different hosts. FTP uses port number 20 to transfer user data, whereas it uses port number 21 to exchange control commands between the two communicating hosts. Here, one will find that the FTP also uses the so‐called user and control plane concept to facilitate the exchange of control and data transfer between two hosts.