Overview EE 122 Internet Design Principles Standardization of protocols Roles played by end systems Ion Stoica TAs Junda Liu DK Moon David Zats http inst eecs berkeley edu ee122 Clients servers peer to peer Architecture layering The End to End Principle Fate Sharing Materials with thanks to Vern Paxson Jennifer Rexford and colleagues at UC Berkeley 1 End System Computer on the Net Protocol Standardization Ensure communicating hosts speak the same protocol Standardization to enable multiple implementations Or the same folks have to write all the software Standardization Internet Engineering Task Force Based on working groups that focus on specific issues Produces Request For Comments RFCs 2 Internet Promoted to standards via rough consensus and running code IETF Web site is http www ietf org RFCs archived at http www rfc editor org De facto standards same folks writing the code P2P file sharing Skype your protocol here Also known as a host 3 Clients and Servers Clients and Servers Client program 4 Running on end host Requests service E g Web browser GET index html Client program 5 Server program Running on end host Running on end host Requests service Provides service E g Web browser E g Web server GET index html Site under construction 6 1 Client Server Communication Client sometimes on Peer to Peer Communication Server is always on Initiates a request to the server when interested E g Web browser on your laptop or cell phone Doesn t communicate directly with other clients Needs to know the server s address Services requests from many client hosts E g Web server for the www cnn com Web site Doesn t initiate contact with the clients Needs a fixed well known address Not always on server at the center of it all Hosts can come and go and change addresses Hosts may have a different address each time Example peer to peer file sharing Any host can request files send files query to find where a file is located respond to queries and forward queries Scalability by harnessing millions of peers Each peer acting as both a client and server 7 The Problem 8 The Problem cont d Many different applications Application email web P2P etc Transmission Media Many different network styles and technologies Circuit switched vs packet switched etc Wireless vs wired vs optical etc How do we organize this mess Skype SSH Coaxial cable NFS Fiber optic HTTP Radio Re implement every application for every technology No But how does the Internet design avoid this 9 Solution Intermediate Layers Network Architecture Introduce intermediate layers that provide set of abstractions for various network functionality technologies A new app media implemented only once Variation on add another level of indirection Application Skype SSH NFS HTTP Intermediate layers Transmission Media 10 Architecture is not the implementation itself Architecture is how to organize structure the elements of the system their implementation What interfaces are supported Where functionality is implemented The modular design of the network Coaxial cable Fiber optic Packet radio 11 Using what sort of abstractions 12 2 Software System Modularity Network System Modularity Like software modularity but Implementation distributed across many machines routers and hosts Must decide Partition system into modules abstractions Well defined interfaces give flexibility E g libraries encapsulating set of functionality E g programming language compiler abstracts away not only how the particular CPU works Hides implementation thus it can be freely changed Extend functionality of system by adding new modules Each layer solely relies on services from layer below Each layer solely exports services to layer above Where state is stored End to End Principle Fate sharing We will address these choices in turn 14 Service what a layer does Service interface how to access the service Interface between layers defines interaction Layering Properties of Layers OSI Model Partition the system What functionality does each module implement Layering A Modular Approach Isolate assumptions Present high level abstractions But can impair performance 13 How to break system into modules but also the basic computational model Well defined interfaces hide information Hides implementation details Layers can change without disturbing other layers Interface for layer above Protocol peer interface how peers communicate to achieve the service Set of rules and formats that specify the communication between network elements Does not specify the implementation on a single machine but how the layer is implemented between machines 15 Physical Layer 1 Application Present Session Transport Network Datalink Physical Service move information between two systems connected by a physical link 16 Data Link Layer 2 Service Enable end hosts to exchange atomic messages with one another Perhaps over multiple physical links Possible other services Interface specifies how to send and receive bits Protocol coding scheme used to represent a bit voltage levels duration of a bit Examples coaxial cable optical fiber links transmitters receivers 17 Application Present Session Transport Network Datalink Physical Using abstract addresses i e not just direct physical connections But using the same framing headers trailers arbitrate access to common physical media reliable transmission flow control Interface send messages frames to other end hosts receive messages addressed to end host Protocols addressing routing Media Access Control MAC e g CSMA CD Carrier Sense Multiple Access Collision Detection 18 3 Inter Network Layer 3 Service Service Inter network across multiple layer 2 networks packet scheduling priority buffer management Interface send packets to specified inter network destinations receive packets destined for end host Protocols define inter network addresses globally unique construct routing tables Application Present Session Transport Network Datalink Physical Provide end to end communication between processes Demultiplexing of communication between hosts Possible other services No longer the same framing all the way Possible other services Works across networking technologies e g Ethernet 802 11 Frame Relay ATM Transport Layer 4 Deliver packets to specified inter network destination Application Present Session Transport Network Datalink Physical Reliability in the presence of errors Timing properties Rate adaption flow control congestion control Interface send message to specific process at given
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