Lec2 - ECE 151 Lecture 2 1 ECE151 Lecture 2 Chapter 2...

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Unformatted text preview: ECE 151 Lecture 2 1 ECE151 Lecture 2 Chapter 2 Communication ECE 151 Lecture 2 2 Layered Protocols (1) Layers, interfaces, and protocols in the OSI model. 2-1 ECE 151 Lecture 2 3 Low-level layers Physical layer: contains the specification and implementation of bits, and their transmission between sender and receiver Data link layer: prescribes the transmission of a series of bits into a frame to allow for error and flow control Network layer: describes how packets in a network of computers are to be routed . Observation: for many distributed systems, the lowest level interface is that of the network layer IP. Note: IP multicasting is generally considered a standard available service. ECE 151 Lecture 2 4 Transport Layer Important: The transport layer provides the actual communication facilities for most distributed systems. Standard Internet protocols: TCP: connection-oriented, reliable, stream-oriented communication UDP: unreliable (best-effort) datagram communication ECE 151 Lecture 2 5 Layered Protocols (2) A typical message as it appears on the network. 2-2 ECE 151 Lecture 2 6 Data Link Layer Discussion between a receiver and a sender in the data link layer. 2-3 ECE 151 Lecture 2 7 Client-Server TCP a) Normal operation of TCP. b) Transactional TCP. 2-4 ECE 151 Lecture 2 8 Application Layer Observation: Many application protocols are directly implemented on top of transport protocols that do a lot of application-independent work. Username + Password Username + Password None (PGP) Security Caching + DNS tricks Caching + DNS tricks Flooding Replication Pull Pull Push Distribution URL Host + path Newsgroup Naming 8-bit + content type 7-bit text + 8-bit binary (user has to guess) 7-bit + MIME Encoding HTTP FTP NNTP Transfer WWW FTP News ECE 151 Lecture 2 9 Middleware Layer Observation: Middleware is invented to provide common services and protocols that can be used by many different applications: A rich set of communication protocols, but which allow different applications to communicate Marshaling and unmarshaling of data, necessary for integrated systems Naming protocols, so that different applications can easily share resources Security protocols, to allow different applications to communicate in a secure way Scaling mechanisms, such as support for replication and caching Note: what remains are truly application-specific protocols ECE 151 Lecture 2 10 Middleware Protocols An adapted reference model for networked communication. 2-5 ECE 151 Lecture 2 11 Conventional Procedure Call a) Parameter passing in a local procedure call: the stack before the call to read b) The stack while the called procedure is active ECE 151 Lecture 2 12 Basic RPC Operation Observations: Application developers are familiar with simple procedure model Well-engineered procedures operate in isolation (black box) There is no fundamental reason not to execute procedures on separate machine...
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Lec2 - ECE 151 Lecture 2 1 ECE151 Lecture 2 Chapter 2...

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