CMU CS 15441 - lecture (49 pages)

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lecture



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lecture

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Pages:
49
School:
Carnegie Mellon University
Course:
Cs 15441 - Computer Networks
Computer Networks Documents

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Lecture 3 Design Philosophy Applications David Andersen School of Computer Science Carnegie Mellon University 15 441 Computer Networks 1 Lecture Overview Last time Protocol stacks and layering OSI and TCP IP models Application requirements from transport protocols Internet Architecture Application examples ftp http Application requirements ilities Sharing 2 Internet Architecture Background The Design Philosophy of the DARPA Internet Protocols David Clark 1988 Fundamental goal Effective network interconnection Goals in order of priority 1 2 3 Continue despite loss of networks or gateways Support multiple types of communication service Accommodate a variety of networks Permit distributed management of Internet resources Cost effective Host attachment should be easy Resource accountability 3 Priorities The effects of the order of items in that list are still felt today E g resource accounting is a hard current research topic Let s look at them in detail 4 Survivability If network disrupted and reconfigured Communicating entities should not care No higher level state reconfiguration Ergo transport interface only knows working and not working Not working complete partition How to achieve such reliability Where can communication state be stored Network Host Failure handing Replication Fate sharing Net Engineering Tough Simple Switches Maintain state Stateless Host trust Less More 5 Fate Sharing Connection State No State State Lose state information for an entity if and only if the entity itself is lost Examples OK to lose TCP state if one endpoint crashes NOT okay to lose if an intermediate router reboots Is this still true in today s network NATs and firewalls Survivability compromise Heterogenous network less information available to end hosts and Internet level recovery mechanisms 6 Types of Service Recall from last time TCP vs UDP Elastic apps that need reliability remote login or email Inelastic loss tolerant apps real time voice or video Others in between or with



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