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Communication

This text explains the concept of layered protocols in the OSI model, including the functions and characteristics of each layer. It also discusses communication protocols at the physical, data link, network, transport, and application layers, as well as the role of middleware protocols.

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Communication

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  1. Communication TANENBAUM-Chapter 2

  2. Layered Protocols (1) 2-1 • Layers, interfaces, and protocols in the OSI model.

  3. Layered Protocols (2) 2-2 • A typical message as it appears on the network.

  4. 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

  5. Data Link Layer 2-3 • Discussion between a receiver and a sender in the data link layer.

  6. 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..

  7. 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

  8. 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

  9. Client-Server TCP 2-4 • Normal operation of TCP. • Transactional TCP.

  10. 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…

  11. 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…

  12. Middleware Protocols 2-5 • An adapted reference model for networked communication.

  13. 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

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