15-441: Computer NetworkingOverviewLearning From FailuresWhy Did They Fail?What Can We Learn?Slide 6Link LayerOverlay RoutingIP MulticastOverlay MulticastOverlay ChallengesCongestion ControlDenial of ServiceBandwidth DoS AttacksSlide 15Network Location ServiceServices For Mobile UsersSlide 18Three Project Areas15-441: Computer NetworkingLecture 26: Networking FutureLecture 26: 12-06-01 2Overview•Learning From Failures •Changes in Various Layers•New Services•What Do I Work On?Lecture 26: 12-06-01 3Learning From Failures•Past failures•Multicast•QoS•MobileIPLecture 26: 12-06-01 4Why Did They Fail?•Scalability problems•Incremental deployment•Interfacing with applications/Building useful services•Debugging problems•Conservative network administratorsLecture 26: 12-06-01 5What Can We Learn?•Avoid same pitfalls•Clever techniques•Fair queuing, announce/suppress protocols, tunneling/encapsulation, etc.Lecture 26: 12-06-01 6Overview•Learning From Failures •Changes in Various Layers•New Services•What Do I Work On?Lecture 26: 12-06-01 7Link 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 linksLecture 26: 12-06-01 8Overlay 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, IPv6Lecture 26: 12-06-01 9IP MulticastKey Architectural Decision: Add support for multicast in IP layerBerkeleyGatechStanfordCMULecture 26: 12-06-01 10Overlay MulticastStanfordOverlay TreeCMUStan-LANStan-ModemBerk2GatechBerk1BerkeleyGatechStan-LANStan-ModemBerk1Berk2CMULecture 26: 12-06-01 11Overlay 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 12Congestion 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 HTTPLecture 26: 12-06-01 13Denial 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 14Bandwidth 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 tracebackLecture 26: 12-06-01 15Overview•Learning From Failures •Changes in Various Layers•New Services•What Do I Work On?Lecture 26: 12-06-01 16Network 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 responseLecture 26: 12-06-01 17Services 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 stylesLecture 26: 12-06-01 18Overview•Learning From Failures •Changes in Various Layers•New Services•What Do I Work On?Lecture 26: 12-06-01 19Three 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
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