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

2. Review Lecture2 5/1/2003 Systems/Techniques to Remember DNS Chord CAN INS GHT IP2Geo IDMaps GNP

3. Review Lecture3 5/1/2003 The Lookup Problem Internet N1N1 N2N2 N3N3 N6N6 N5N5 N4N4 Publisher Key=“title” Value=MP3 data… Client Lookup(“title”) ? Problem in DNS, P2P, routing, etc. Sensor networks: how to find sensor readings?

4. Review Lecture4 5/1/2003 DNS: Query Routing Client Local DNS server root & edu DNS server ns1.cmu.edu DNS server www.cs.cmu.edu NS ns1.cmu.edu www.cs.cmu.edu NS ns1.cs.cmu.edu A www=IPaddr ns1.cs.cmu.edu DNS server

5. Review Lecture5 5/1/2003 DNS: Subsequent Query Routing Client Local DNS server root & edu DNS server cmu.edu DNS server cs.cmu.edu DNS server ftp.cs.cmu.edu ftp=IPaddr ftp.cs.cmu.edu

6. Review Lecture6 5/1/2003 Chord: Query Routing 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 0 1 2 3 4 5 6 7 i id+2 i succ 0 2 2 1 3 6 2 5 6 Succ. Table i id+2 i succ 0 3 6 1 4 6 2 6 6 Succ. Table i id+2 i succ 0 1 1 1 2 2 2 4 0 Succ. Table 7 Items 1 i id+2 i succ 0 7 0 1 0 0 2 2 2 Succ. Table query(7)

7. Review Lecture7 5/1/2003 CAN: Query Routing Properties  Routing table size O(d)  Guarantees that a file is found in at most d*n 1/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 1 234 5 670 1 2 3 4 5 6 7 0 n1 n2 n3 n4 n5 f1 f2 f3 f4

8. Review Lecture8 5/1/2003 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

9. Review Lecture9 5/1/2003 INS Architecture: Message routing using intentional names Name resolver Overlay network of resolvers Client Intentional anycast Intentional multicast Name Service Late binding Name with message

10. Review Lecture10 5/1/2003 INS Lookups Two styles of message delivery  Anycast  Multicast Two types of lookup  Early binding  Late binding

11. Review Lecture11 5/1/2003 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)

12. Review Lecture12 5/1/2003 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!

13. Review Lecture13 5/1/2003 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)

14. Review Lecture14 5/1/2003 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)

15. Review Lecture15 5/1/2003 Sharing Measurements IDMaps [Francis et al ’99] Probe Server A B 50msA/B

16. Review Lecture16 5/1/2003 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 y (x 2,y 2,z 2 ) x z (x 1,y 1,z 1 ) (x 3,y 3,z 3 ) (x 4,y 4,z 4 )

17. Review Lecture17 5/1/2003 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.

18. Review Lecture18 5/1/2003 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?

19. Review Lecture19 5/1/2003 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.