lec2 - ECE 333 Introduction to Communication Networks Fall...

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1 ECE 333: Introduction to Communication Networks Fall 2002 Lecture 2: Network Architectures Layering Motivation Terminology Examples 2 Many issues to address in networks: Addressing, connection setup, code conversion, message segmentation, routing, flow control, scheduling, multiplexing, medium access, ordering messages, framing, error control, synchronization, encoding, multiplexing, security, billing, compression, … ± Very complex systems! How to deal with this complexity?
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3 Modularity Useful method for dealing with complexity is by using functional modularity. Break complex problem into simpler sub-problems. Use “black box” abstraction of sub-problems. Example: Computer --- Processor, memory, bus,… Processor --- Control unit, arithmetic unit, I/O unit,… Arithmetic unit --- Adders, accumulators, … 4 Hierarchical Layering – a type of functional modularity useful in communication networks. Network functions are viewed as sequence of layers. Example: Post office
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5 Another Example : Modem/analog link/modem can be viewed as a "vitrual bit pipe". Analog communication link Modem Modem User User ---------------------------------- ----------- Virtual bit pipe The modem/link/modem is lower layer ; it provides a service to higher layer users. 6 Higher layers more abstract level of service. Analog communication link Modem Modem Virtual bit pipe Layer 2 Layer 2 Packet pipe
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7 Notes: Slide 1: By "network architecture", we mean a global view of the network that describes how the various operations are organized. Completely specifying a layered architecture requires specifying a set of protocols for each layer. Slide 5: The service offered by the modem-link-modem can be described as a "bit pipe"; more detailed characteristics of this service may include specification of the transmission rate, the error rate, the delay, etc. Other examples of layering are given in Section 2.1 of the text. Side 6: Two interesting characteristics about layered architectures in data networks are (1) the systems that implement the services at each layer are distributed and (2) to implement the services, these systems must communicate over unreliable links with delays. 8 Terminology Peers or peer processes : Members of the same layer at different locations. Protocol: Set of rules for how peers interact. Service: Function performed by layer N for layer N+1. Service Interface: Rules for communicating about services. Protocol Stack: The set of protocols used (one per layer) Network Architecture or Network Reference Model: The set of layers used for a network
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9 Generic Example Host A Host B Layer 5 Layer 4 Layer 3 Layer 2 Layer 1 Layer 5 Layer 4 Layer 3 Layer 2 Layer 1 Layer 5 protocol Layer 4 protocol Layer 3 protocol Layer 2 protocol Layer 1 protocol Layer 4/5 interface Layer 3/4 interface Layer 2/3 interface Layer 1/2 interface Physical medium 10 Example - Simple Mail Transfer Protocol (SMTP)
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lec2 - ECE 333 Introduction to Communication Networks Fall...

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