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15-441: Computer Networking

Explore the past failures, changes in different networking layers, new services, and areas to work on in computer networking. Learn from mistakes, clever techniques, and innovative solutions. Discover the impact of overlay routing, IP multicast, congestion control, denial-of-service attacks, and network location services. Dive into the challenges and opportunities in mobile networking, sensor networks, and wide-area distributed applications.

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15-441: Computer Networking

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  1. 15-441: Computer Networking Lecture 26: Networking Future

  2. Overview • Learning From Failures • Changes in Various Layers • New Services • What Do I Work On? Lecture 26: 12-06-01

  3. Learning From Failures • Past failures • Multicast • QoS • MobileIP Lecture 26: 12-06-01

  4. Why Did They Fail? • Scalability problems • Incremental deployment • Interfacing with applications/Building useful services • Debugging problems • Conservative network administrators Lecture 26: 12-06-01

  5. What Can We Learn? • Avoid same pitfalls • Clever techniques • Fair queuing, announce/suppress protocols, tunneling/encapsulation, etc. Lecture 26: 12-06-01

  6. Overview • Learning From Failures • Changes in Various Layers • New Services • What Do I Work On? Lecture 26: 12-06-01

  7. Link Layer • Optical links • Multiple wavelengths on a single fiber (WDM) • MPLS applied to wavelengths  MPλS • No longer broadcast • All optical networks • No buffering!!  How does this affect other protocols • Mobile/wireless links Lecture 26: 12-06-01

  8. Overlay Routing • Basic idea: • Treat multiple hops through IP network as one hop in overlay network • Run routing protocol on overlay nodes • Why? • For performance – can run more clever protocol on overlay • For efficiency – can make core routers very simple • For functionality – can provide new features such as multicast, active processing, IPv6 Lecture 26: 12-06-01

  9. IP Multicast Gatech Stanford CMU Berkeley Key Architectural Decision: Add support for multicast in IP layer Lecture 26: 12-06-01

  10. Overlay Multicast CMU Gatech Stan-LAN Stanford Stan-Modem Berk1 Berkeley Berk2 Overlay Tree Stan-LAN Gatech Stan-Modem CMU Berk1 Lecture 26: 12-06-01 Berk2

  11. Overlay Challenges • “Routers” no longer have complete knowledge about link they are responsible for • How do you build efficient overlay • Probably don’t want all N2 links – which links to create? • Without direct knowledge of underlying topology how to know what’s nearby and what is efficient? Lecture 26: 12-06-01

  12. Congestion Control • Is AIMD the right choice for everyone? • What are the requirements on choices  TCP-friendliness • Non-linear controls • Rate-based controls • Fixing poor interaction with HTTP Lecture 26: 12-06-01

  13. Denial of Service • Objective of attack: make a service unusable, usually by overloading the server or network • Example: SYN flooding attack • Send SYN packets with bogus source address • Server responds with SYNACK keeps state about TCP half-open connection • Eventually server memory is exhausted with this state • Solution: SYN cookies – make the SYNACK contents purely a function of SYN contents, therefore, it can be recomputed on reception of next ACK • More recent attacks have used bandwidth floods • How do we stop these? Lecture 26: 12-06-01

  14. Bandwidth DoS Attacks • Possible solutions • Ingress filtering – examine packets to identify bogus source addresses • Link testing – how routers either explicitly identify which hops are involved in attack or use controlled flooding and a network map to perturb attack traffic • Logging – log packets at key routers and post-process to identify attacker’s path • ICMP traceback – sample occasional packets and copy path info into special ICMP messages • IP traceback Lecture 26: 12-06-01

  15. Overview • Learning From Failures • Changes in Various Layers • New Services • What Do I Work On? Lecture 26: 12-06-01

  16. Network Location Service • Desirable to lookup performance between hosts • Why? • How to predict? • Based on historical measurements • Based on on-demand probing • What exactly is performance? • Bandwidth • Delay • Application response Lecture 26: 12-06-01

  17. Services For Mobile Users • Why? • (Example) Mobile users are more likely to search for services near them • Not well suited to administratively organized Internet systems • Example • Build a wide area service discovery that can support multiple search styles Lecture 26: 12-06-01

  18. Overview • Learning From Failures • Changes in Various Layers • New Services • What Do I Work On? Lecture 26: 12-06-01

  19. Three Project Areas • Congestion Control • Solving interaction between HTTP and TCP • Using congestion control to implement QoS • Mobile Networking • Making protocols adapt to dynamic conditions • Helping “ubiquitous” networks evolve • Sensor networks • Wide-Area Distributed Applications • Tools to help developers build large distributed applications • Overlay multicast Lecture 26: 12-06-01

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