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CS 268: Computer Networking

CS 268: Computer Networking. L-23 Course Wrap-up. Goals and Objectives. Understand state-of-the-art in network protocols, architectures, and applications Process of networking research Constraints and thought processes for networking research Problem Formulation—Approach—Analysis—Results

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CS 268: Computer Networking

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  1. CS 268: Computer Networking L-23 Course Wrap-up

  2. Goals and Objectives • Understand state-of-the-art in network protocols, architectures, and applications • Process of networking research • Constraints and thought processes for networking research • Problem Formulation—Approach—Analysis—Results • Different from undergraduate networking (EECS 122) • i.e., training network programmers vs. training network researchers

  3. Class Topic Coverage • Little on physical and data link layer • Little on undergraduate material • Supposedly you already know this, though some revisiting/overlap is unavoidable • Focus on the why, not the what • Focus on network-to-application layer • We dealt with: • Protocol rules and algorithms, tradeoffs, rationale • Routing, transport, DNS resolution, … • Network extensions and next generation architecture • Wireless, mobile, sensor, …

  4. Traditional Layering Internet architecture Routing (IP) Transport (TCP) Queue management (FQ, RED) Naming (DNS) Recent Topics Multicast Mobility/wireless Active networks QoS Network measurement Overlay networks P2P applications Datacenter networking Lecture Topics Italics topics on Quiz #2

  5. What is the Objective of Networking? • Communication between applications on different computers • Must understand application needs/demands • Traffic data rate, pattern (bursty or constant bit rate), target (multipoint or single destination, mobile or fixed) • Delay and loss sensitivity • Other application-support services • Overlays, Active Networks, Data-oriented, …

  6. Back in the Old Days…

  7. Packet Switching (Internet) Packets

  8. Packet Switching • Interleave packets from different sources • Statistical multiplexing to use resources on demand • Supports multiple applications types • Accommodates bursty traffic via queues • Store and forward • Packets are self contained units • Can use alternate paths – reordering • Effects of contention: congestion and delay • Semester readings on Fair Queuing, Router Design, Network Topology and Network Measurement

  9. Internet[work] • A collection of interconnected networks • Host: network endpoints (computer, PDA, light switch, …) • Router: node that connects networks • Internet vs. internet Internet[work]

  10. Challenge • Many differences between networks • Address formats • Performance – bandwidth/latency • Packet size • Loss rate/pattern/handling • Routing • How to translate between various network technologies? • Gateways

  11. Extensions to the Network • New kinds of networks within the Internet • Mobile • Wireless • Sensor • Delay Tolerant • Content Distribution/Data Oriented Networks • Semester readings on Roofnet, Ad hoc and sensor net routing, DTNs, CDNs, DOT, etc.

  12. How To Find Nodes? Internet Computer 1 Computer 2 Need naming and routing

  13. Naming What’s the IP address for www.cmu.edu? It is 128.2.11.43 Computer 1 Local DNS Server Translates human readable names to logical endpoints

  14. Extensions to the Network Architecture • Naming • DNS as an Overlay Network • Problems with Host-to-IP Address bindings • Problems with Service-to-Host bindings • Solutions based on the idea of an extra level of indirection: flat identifiers plus resolution based on DHT lookup • Semester readings on DNS and on flat names and DHTs in the context of i3, DOA, etc.

  15. Routing Routers send packet towards destination H R H R H R R R R H R H: Hosts R: Routers R H

  16. Extensions to the Network Architecture • Forwarding • Problems with Internet routing • Beyond point-to-point routing: multicast, mobility, alternative schemes and metrics for wireless/sensor nets, delay tolerant nets, etc. • Indirection schemes and intermediaries (“performance enhancing proxies”) to implement new forms of forwarding • Semester readings on Internet topology, multicast, wireless, i3, DTN, DOA, policy-aware switching, network measurement

  17. Meeting Application Demands • Reliability • Corruption • Lost packets • Flow and congestion control • Fragmentation • In-order delivery • Etc. …

  18. What if the Data gets Corrupted? Problem: Data Corruption GET index.html GET windex.html Internet Solution: Add a checksum X 0,9 9 6,7,8 21 4,5 7 1,2,3 6

  19. What if Network is Overloaded? • Short bursts: buffer • What if buffer overflows? • Packets dropped • Sender adjusts rate until load = resources  “congestion control” Problem: Network Overload Solution: Buffering and Congestion Control

  20. What if the Data gets Lost? Problem: Lost Data GET index.html Internet Solution: Timeout and Retransmit GET index.html GET index.html Internet GET index.html

  21. What if the Data Doesn’t Fit? Problem: Packet size • On Ethernet, max IP packet is 1.5kbytes • Typical web page is 10kbytes Solution: Fragment data across packets ml x.ht inde GET GET index.html

  22. What if the Data is Out of Order? Problem: Out of Order ml inde x.ht GET GET x.htindeml Solution: Add Sequence Numbers ml 4 inde 2 x.ht 3 GET 1 GET index.html

  23. Lots of Functions Needed • Link • Multiplexing • Routing • Addressing/naming (locating peers) • Reliability • Flow control • Fragmentation • Etc. …

  24. What is Layering? • Modular approach to network functionality • Example: Application Application-to-application channels Host-to-host connectivity Link hardware

  25. Protocols • Module in layered structure • Set of rules governing communication between network elements (applications, hosts, routers) • Protocols define: • Interface to higher layers (API) • Interface to peer • Format and order of messages • Actions taken on receipt of a message

  26. Layering Characteristics • Each layer relies on services from layer below and exports services to layer above • Interface defines interaction • Hides implementation - layers can change without disturbing other layers (black box)

  27. Application-Oriented Networking • All kinds of new application-specific routing and transport layers • Sensor network dissemination protocols • Content distribution/data oriented networks • Overlay networks • Active networks • Middleboxes/”Performance Enhancing Proxies” • Layering and E2E assumptions questioned and revised

  28. Quo Vadis Networking? • GENI: new architecture for Next Generation • New naming and forwarding as foundation • Security and authenticity from first principles • Experimentation in upper layers, e.g., DTN • Refocus from wide-area to local-area • Unified telephony and data, wired/wireless • Datacenters for web and batch parallel apps • O(10,000) node DC and enterprise networks • New addressing, transport opportunities

  29. What Next? • Thursday, 4 December: Quiz #2 • Friday, 12 December: Research Project Poster Session -- 12-2 PM in Soda 6th Floor • Poster more or less equivalent to 9 slide research talk • Remember the Heilmeyer Questions! • Monday, 15 December: 5 PM Project Reports • Specification on the web, 10-20 pages

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