Functions of the Presentation Layer Functions of the Application Layer From application layer =m- Network virtual terminal -remote log- in other host in the internel File transfer, access, and management-store, retrieve or manage the o session layer ation layer is concerned with the syntax and semantics ss for global information and services e.g. HyperTextTransferProtocol(http) The presentation layer changes (encodes) the sender dependent format of the message into transform the original nformation into an encrypted form to assure privacy Compression-Data compression can reduce the number of bits to be transmitted, which is important for multimedia transmission. Summary for the functions of OSI-layers Chapter 1: Introduction Chapter goal: rk ba TCP/IP protocols stack review Client-server application dde nodes node odel and software design a Concurrent processing in TCP/IP Protocol Suite TCP/IP Protocol Architecture (1) Dominant co architecture Communication between processes or Specified and extensively used End to end or transport layer(TCP/UDP/.) before osi Developed by research funded US May include reliability mechanism(TCP) Department of d efense Hides detail of underlying network Used by the Internet Network Layer Routing of data6 哈工大计算机学院 李全龙 Network Application Development 1: Introduction 31 Functions of the Presentation Layer P-PDU Encoded, encrypted, and compressed data PH A- PDU Presentation layer To session layer From application layer P-PDU Decoded, decrypted, and decompressed data PH A- PDU Presentation layer From session layer To application layer The presentation layer is concerned with the syntax and semantics of the information exchange between two systems. • Translation - The presentation layer changes (encodes) the sender￾dependent format of the message into a common format that can be readable by any receiving system • Encryption - The presentation layer can transform the original information into an encrypted form to assure privacy. • Compression - Data compression can reduce the number of bits to be transmitted, which is important for multimedia transmission. 哈工大计算机学院 李全龙 Network Application Development 1: Introduction 32 Functions of the Application Layer This layers enable the user (human or software) to access the network by user interfaces. Sometimes, No header or trailers are added at this layer. Typical services provided by this layer are: • Network virtual terminal - remote log-in other host in the internet • File transfer, access, and management - store, retrieve or manage the files from a remote computer. e.g. File Transfer Protocol (FTP) • Mail services - e.g. Simple Mail Transfer Protocol (SMTP) • Directory services - access for global information and services e.g. Hyper Text Transfer Protocol (HTTP) Application layer User A (U.S.) HTTP FTP SMTP L7 data Application layer User B (Africa) HTTP FTP SMTP L7 data 哈工大计算机学院 李全龙 Network Application Development 1: Introduction 33 Application Presentation Session Transport Network Data link Physical Summary for the functions of OSI-layers allow access to network Translate, encrypt, and compress data Establish, manage, and terminate session Provide reliable end-to￾end message delivery and Move packets from error recovery source to destination; to provide internetworking Organize bits into frames; to provide node-to-node Transmit bits over a delivery medium; to provide mechanical and electrical specification 哈工大计算机学院 李全龙 Network Application Development 1: Introduction 34 Chapter 1: Introduction Chapter goal: „ Network basics „ TCP/IP protocols stack review „ Client-server application model and software design „ Concurrent processing in client-server model 哈工大计算机学院 李全龙 Network Application Development 1: Introduction 35 TCP/IP Protocol Suite „ Dominant commercial protocol architecture „ Specified and extensively used before OSI „ Developed by research funded US Department of Defense „ Used by the Internet 哈工大计算机学院 李全龙 Network Application Development 1: Introduction 36 TCP/IP Protocol Architecture(1) „ Application Layer „ Communication between processes or applications „ End to end or transport layer (TCP/UDP/…) „ End to end transfer of data „ May include reliability mechanism (TCP) „ Hides detail of underlying network „ Network Layer „ Routing of data