A8_Comm-Ch4 - Chapter 4 Communication Fundamentals...

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Chapter 4: Communication Fundamentals
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Introduction In a distributed system, processes run on different machines. Processes can only exchange information through message passing. harder to program than shared memory communication Successful distributed systems depend on communication models that hide or simplify message passing
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Overview Message-Passing Protocols OSI reference model TCP/IP Others Higher level communication models Remote Procedure Call (RPC) Message-Oriented Middleware (time permitting) Data Streaming (time permitting)
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Introduction A communication network provides data exchange between two (or more) end points. Early examples: telegraph or telephone system. In a computer network, the end points of the data exchange are computers and/or terminals. (nodes, sites, hosts, etc., …) Networks can use switched, broadcast, or multicast technology
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Network Communication Technologies – Switched Networks Usual approach in wide-area networks Partially (instead of fully) connected Messages are switched from one segment to another to reach a destination. Routing is the process of choosing the next segment. X Y
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Circuit Switching v Packet Switching Circuit switching is connection-oriented (think traditional telephone system) Establish a dedicated path between hosts Data can flow continuously over the connection Packet switching divides messages into fixed size units (packets) which are routed through the network individually. different packets in the same message may follow different routes.
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Pros and Cons Advantages of packet switching: Requires little or no state information Failures in the network aren't as troublesome Multiple messages share a single link Advantages of circuit switching: Fast, once the circuit is established Packet switching is the method of choice since it makes better use of bandwidth.
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A Compromise Virtual circuits: based on packet-switched networks, but allow users to [appear to] establish a connection between two nodes and then communicate via a stream of bits, much as in circuit switching Slower than actual circuit switching because it operates on a shared medium Layer 4 (using TCP over IP) versus Layer 2/3 virtual circuits (more secure, not necessarily faster or more efficient)
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Other Technologies Broadcast: send message to all computers on the network (primarily a LAN technology) Multicast: send message to a group of computers Broadcast Multicast – shared Links for efficiency
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LANs and WANS A LAN (Local Area Network) spans a small area – one floor of a building to several buildings WANs (Wide Area Networks) cover a wider area, connect LANS LANs are faster and more reliable than WANs, but there is a limit to how many nodes can be connected, how far data can be transmitted.
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Protocols A protocol is a set of rules that defines how two entities interact. For example: HTTP, FTP, TCP/IP,
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This note was uploaded on 12/14/2011 for the course CS 690 taught by Professor Staff during the Fall '11 term at University of Alabama - Huntsville.

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A8_Comm-Ch4 - Chapter 4 Communication Fundamentals...

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