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15-829A/18-849B/95-811A/19-729A Internet-Scale Sensor Systems: Design and Policy

15-829A/18-849B/95-811A/19-729A Internet-Scale Sensor Systems: Design and Policy. Review. Systems/Techniques to Remember. DNS Chord CAN INS GHT IP2Geo IDMaps GNP. The Lookup Problem. N 2. N 1. N 3. Key=“title” Value=MP3 data…. Internet. ?. Client. Publisher. Lookup(“title”).

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15-829A/18-849B/95-811A/19-729A Internet-Scale Sensor Systems: Design and Policy

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  1. 15-829A/18-849B/95-811A/19-729AInternet-Scale Sensor Systems: Design and Policy Review

  2. Systems/Techniques to Remember • DNS • Chord • CAN • INS • GHT • IP2Geo • IDMaps • GNP Review Lecture

  3. The Lookup Problem N2 N1 N3 Key=“title” Value=MP3 data… Internet ? Client Publisher Lookup(“title”) N4 N6 N5 • Problem in DNS, P2P, routing, etc. • Sensor networks: how to find sensor readings? Review Lecture

  4. www.cs.cmu.edu NS ns1.cmu.edu NS ns1.cs.cmu.edu A www=IPaddr DNS: Query Routing root & edu DNS server www.cs.cmu.edu ns1.cmu.edu DNS server Local DNS server Client ns1.cs.cmu.edu DNS server Review Lecture

  5. DNS: Subsequent Query Routing root & edu DNS server ftp.cs.cmu.edu cmu.edu DNS server Local DNS server Client ftp.cs.cmu.edu cs.cmu.edu DNS server ftp=IPaddr Review Lecture

  6. Chord: Query Routing Succ. Table • Properties • Routing table size O(log(N)), where N is the total number of nodes • Guarantees that a file is found in O(log(N)) steps • Upon receiving a query for item id, a node • Check whether stores the item locally • If not, forwards the query to the largest node in its successor table that does not exceed id Items 7 i id+2i succ 0 1 1 1 2 2 2 4 0 0 Succ. Table Items 1 1 i id+2i succ 0 2 2 1 3 6 2 5 6 7 query(7) 6 2 Succ. Table i id+2i succ 0 7 0 1 0 0 2 2 2 Succ. Table i id+2i succ 0 3 6 1 4 6 2 6 6 5 3 4 Review Lecture

  7. CAN: Query Routing • Properties • Routing table size O(d) • Guarantees that a file is found in at most d*n1/d steps, where n is the total number of nodes • If d = log n  O(log n) steps • Each node knows its neighbors in the d-space • Forward query to the neighbor that is closest to the query id • Example: assume n1 queries f4 7 6 n5 n4 n3 f4 5 4 f1 3 n2 n1 2 f3 1 f2 0 0 2 3 4 6 7 5 1 Review Lecture

  8. Name Lookup • What do names/descriptions look like? • How is the searching done? • What type of searches? • Search for particular service, browse available services or find collection of services (composition)? • Exact match queries or richer queries? • Find any one matching instance or find all matching instances? • Which instance to choose  what are the right metrics Review Lecture

  9. INS Architecture: Message routing using intentional names Client Service Name Name resolver Late binding Name with message Intentional multicast Intentional anycast Overlay network of resolvers Name Review Lecture

  10. INS Lookups • Two styles of message delivery • Anycast • Multicast • Two types of lookup • Early binding • Late binding Review Lecture

  11. Storage Models for Sensor Networks • Local • Local storage has greatest total message count as n grows • External • External storage always sends fewer messages than DCS (Data Centric Storage) • Data Centric • When many more event types detected than queried for, DCS has least hotspot message count • DCS permits summarization of events (return multiple events in one packet) Review Lecture

  12. Geographic Hash Table • Two operations supported: • Put(k;v) stores v, the event, according to key k • Get(k) retrieves the value associated with key k • Hash a key k into geographic coordinates; store and retrieve events for that key at that location • Spreads load evenly across key space! Review Lecture

  13. Network Mapping • Difficult to find nearby nodes quickly and efficiently • Huge number of paths to measure • TCP bandwidth and RTT probes are time-consuming • No clean mapping of IP address  location (geographic or network topology) Review Lecture

  14. IP2Geo Techniques • GeoTrack • DNS-based: traceroute names  locations • GeoPing • Latency-based: match host to nearest host with known location • GeoCluster • BGP-based: try to cluster host by announced address prefixes (with some heuristic corrections) Review Lecture

  15. A/B 50ms Server Probe Probe Probe Sharing MeasurementsIDMaps [Francis et al ’99] A B Review Lecture

  16. Global Network Positioning (GNP) Coordinates • Model the Internet as a geometric space (e.g. 3-D Euclidean) • Characterize the position of any end host with geometric coordinates • Use geometric distances to predict network distances (x2,y2,z2) y (x1,y1,z1) x z (x4,y4,z4) (x3,y3,z3) Review Lecture

  17. Some Sample Questions • Imagine a Chord system using 3-bit ids. Let there be 3 nodes participating with IDs 0, 3 and 7. Fill in the finger table for node 0. • There are three forms of P2P lookup algorithms: centralized, flooding-based and routing-based. Which of the following statements is true about these algorithms? • Flooding-based and centralized systems can support much richer queries (regular expressions, wildcards) than routing-based systems. • Routing-based systems are more scalable than flooding-based systems since they produce less traffic per search. • Centralized systems are less prone to failure than flooding-based systems. • Routing-based systems ensure that a client finds the copy of a file that is closest to it in the network. Review Lecture

  18. Some Sample Questions • Harry begins by replacing the Web proxy with a global distributed hash table (DHT)-based lookup system. When a client makes a HTTP request, it simply performs a DHT-based lookup for the request among all participating client caches in the world. If the object is found, the client retrieves the object from the participating cache. Ignore the impact of this system on server load for the following questions. • Harry wants to ensure that no client is forced to keep track of more than 10 other clients. Which of the DHT solutions discussed in class is best suited for this and why? • Given this choice of DHT, how many DHT-level hops are needed for a system with N total clients? Review Lecture

  19. Some Sample Questions • Which of following is true about DNS? • While resolving the A-record for the name golden-gate.ne.mediaone.net, a name server that does not have the A-record cached may not need to go to the root or gTLD server. • While resolving the A-record for the name golden-gate.ne.mediaone.net, suppose a name server contacts the name server for mediaone.net. Now, if the query packet sent here is lost, a new lookup originating from the root is initiated. Review Lecture

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