EE450-U2-Protocols&Layering-Nazarian-Spring10

EE450-U2-Protocols&Layering-Nazarian-Spring10 - EE450...

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EE450 Computer Networks Network Protocols and Layering Shahin Nazarian Spring 2010
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Shahin Nazarian/EE450/Spring 2010 2 An Example a Human Protocol: Tasks Involved in Sending a Letter
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Shahin Nazarian/EE450/Spring 2010 What is a Protocol? A protocol can be defined as the rules, conventions, standards governing the syntax, semantics, and synchronization of communication. Another words, protocols are sets of rules, (or a sequence of events) that control or enable (preferably reliable and) recognizable transfer of information among communication end points Hi Hi Got the time? 2:00 TCP connection request TCP connection response Get http://www.awl.com/kurose-ross <file> time a human protocol a computer network protocol 3
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Shahin Nazarian/EE450/Spring 2010 4 Protocol Note that protocol represents an agreement among communication devices. Without a protocol devices may be connected but not communicating Protocols are devised such that the system including all its hardware and software products (which in general are from different vendors) will be able to operate as long as they adhere to the standards in the protocol This guarantees marketability for vendor products One main shortcoming of a protocol is that it takes a long time to be devised and standardized, therefore by the time the protocol is ready to be commercialized, the technology may be outdated
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Shahin Nazarian/EE450/Spring 2010 5 ISO and OSI
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Shahin Nazarian/EE450/Spring 2010 6 Network Expectations and Goals From the user point of view (application programmer or end User: network delivery should be reliable, and recognizable and in a reasonable (and predictable) time The network designer looks for cost-effective designs to make the design affordable; and makes sure the resources such the CPUs, memories and bandwidth are efficiently and fairly used The network provider cares about billing issues, simplicity of use, straightforward fault detection and isolation (i.e., the faults that force down the network.) It also cares about administrative and management issues
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Shahin Nazarian/EE450/Spring 2010 OSI Layers OSI is the most popular packet-based structure of layers, or protocol stack The functionality of communications in OSI is divided into 7 layers which are counted from bottom to top 7
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Shahin Nazarian/EE450/Spring 2010 Why Layering? Networking (communications) is overall a very complicated task and involves very complex steps such as transmission, error detection and recovery, routing, synchronization, etc. One way to handle networking was to write a big piece of code (program) that would perform all the tasks, without organizing it into subroutines, sub-functions. This would be very hard to enhance if needed and/or debug in case of error in the program 8 Networking Tasks in one layer
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Shahin Nazarian/EE450/Spring 2010 Why Layering? (Cont.) Another choice the network designers had was to divide the networking tasks into subtasks and write programs each of which responsible only for one of those subtasks. Each of those
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This note was uploaded on 09/04/2010 for the course EE 450 at USC.

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EE450-U2-Protocols&Layering-Nazarian-Spring10 - EE450...

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