Communication TANENBAUM-Chapter 2
Layered Protocols (1) 2-1 • Layers, interfaces, and protocols in the OSI model.
Layered Protocols (2) 2-2 • A typical message as it appears on the network.
Layered Protocols (3) • Connection-oriented • Connectionless • Lower layer protocols • Physical Layer: • standardization of electrical, mechanical and signaling interfaces, • It does not handle errors • e.g. RS-232 is standard for physical layer serial communication… Manchester encoding in LAN is another… • Data Link Layer: can detect and correct certain errors in bit strings. • It groups bits into so called frames and adds checksum fields to detect errors • Sequencing is used to identify the frames for error handling
Data Link Layer 2-3 • Discussion between a receiver and a sender in the data link layer.
Network Layer • On LAN: no need for locating the receiver, as it is on the same LAN as the sender, so no routing is required • On wide area network finding the destination is an important task • IP protocol is used for finding the route to the destination; it is part of TCP/IP suit • It is a connectionless protocol • Connection oriented protocols at this level have also gained important ground! ATM networks use virtual circuits..
Transport Protocols (1) • Transport layer is an end-to-end protocol, contrary to the lower layers of protocol • It is a connection-oriented reliable protocol • Transport layer should guarantee the delivery of the message provided by the application. • Applications use the interface provided by the transport layer protocol to access the network… • TCP/IP suit has TCP as connection oriented reliable protocol • TCP/IP suit also provide UDP as the transport level unreliable connectionless protocol
Transport Protocols (2) • Transport protocols, in general can be tuned to the applications • Client-server applications often use transport protocols • TCP is more common than UDP in TCP/IP protocol suit, for this purpose • TCP for transactions can be more efficient as in the next figure
Client-Server TCP 2-4 • Normal operation of TCP. • Transactional TCP.
Higher-Level protocols • IN practice two of the higher layers are not used much… • Session layer does not functionally worth the overhead; • Presentation layer is concerned with meaning associated to the data: e.g., decryption/ encryption • Application protocols can integrate session as well as presentation functionality…
Application Protocols • It includes standard common applications such as ftp, email, terminal emulation, Internet FTP, HTTP • Middleware protocols are use to provide various middleware services that do not fit in transport layer. • Examples: authentication and authorization protocols, distributed transaction commit protocols, distributed locking protocol, remote procedure calls (RPC), remote object invocation, message queuing services, continuous media streams • RPC stands out both historically and in commonality…
Middleware Protocols 2-5 • An adapted reference model for networked communication.
Conventional Procedure Call Read(fd,buf,nbytes) • Parameter passing in a local procedure call: the stack before the call to read • The stack while the called procedure is active