7DS - Node Cooperation and Information Exchange in Mostly Disconnected Networks Suman Srinivasan, Arezu Moghadam, Se Gi Hong, Henning Schulzrinne IRT Lab, Computer Science, Columbia University

Problems with Wide Area Wireless currently hard to deploy across city or large area Problem: How can mobile devices / gadgets get information while on the move? Use local peer-to-peer wireless networks to exchange information –Peers can get information they do not have from another peer Solution: 7DS!

How 7DS Works 1.When devices are in the same BSS (Basic service set) of ad-hoc network, they discover each other using service discovery of Zeroconf zeroconf

How 7DS Works Internet 2.If there is no Internet connection, the devices can communicate with each other to exchange information

Web Delivery Model 7DS core functionality: Emulation of web content access and delivery

Design Peer-to-peer network set up using zeroconf –Protocol enables devices to communicate with each other without a DHCP server, a DNS server and a Directory server Proxy server serves content Search engine searches for local data MTA store and forward In progress: File synchronization, BBS

Store and Forward Forwarding in the ad-hoc network Acts as an MTA

Search Engine Provides ability to query self for results Searches the cache index using Swish-e library Presents results in any of three formats: HTML, XML and plain text Similar in concept to Google Desktop

Query Multicast Engine Used to actually exchange information among peers Requesting peer broadcasts a query to the network Responding peers reply if they have information –Send encoded string with list of matching items Requesting peer retrieves suitable information

File Synchronization SRV : 7ds-fs1.filesync._7ds._udp.local. 7ds-device1.local:2525 TXT : file1.xml TXT : file2.xml SRV : 7ds-fs2.filesync._7ds._udp.local. 7ds-device2.local:2525 TXT : word.doc TXT : presentation.ppt File1.xml File2.xml Word.doc Presentation.ppt “I want Word.doc and presentation.ppt” “I want File1.xml and file2.xml” Word.doc Presentation.ppt File1.xml File2.xml SERVICE ANNOUNCEMENT SERVICE RESOLUTIONFILE SYNCHRONIZATION USING RSYNC PROTOCOL

Conclusion 7DS allows data retrieval and transmission, even in absence of Internet Exchange of information within local network –Nodes that eventually connect to larger network facilitate new information exchange No user intervention unless absolutely necessary New step in practical, large-scale wireless networking with gadgets? –Remains to be seen

Backup Slides

Working

Search Engine Implementation Client (Browser) Proxy Server Search Engine Swish Library 1. Browser enters query 2. Search engine uses swish-e library to search cache 3. Swish-e library gets results 4. Results returned to browser in appropriate format (HTML, XML…) Cache Manager Frequently checks cache for changes; If there is a change, it reindexes the cache. Cache

Multicast – Requesting Peer Client (Browser) Add Query CGI SQLite Library DB 1. Browser enters query 2. CGI script adds query to local SQLite database 3. Query Scheduler Bcast frequently retrieves queries from DB Query Scheduler Bcast 4. Query Scheduler Bcast multicasts XML-encoded string of recent queries to network

Multicast – Responding Peer Query Receiver 4. Query Receiver sends XML- encoded string of results to requesting peer via UDP Swish Library 3. Swish-e library gets results Cache 2. Query Receiver uses swish-e library to search cache 1. Query Receiver listens for and receives multicast query

Multicast – Requesting Peer Client (Browser) Results Page CGI SQLite Library DB 4. The results are returned to the browser 3. Results page refreshes often, getting latest results 2. Adds results to DB Result Receiver 1. Result Receiver listens for and receives XML- encoded results

Old vs. Current Design Old version, 0.9 (presented in paper) –Independent binaries, no modules –Difficulty porting to different platforms –Universal GUI difficult due to messages being event-based; polling inefficient New version 2.0 –Modular; easy to make more “plugins” –Cross-platform –Richer GUI with service discovery

Transition from mcast to Bonjour Operation of multicast query system –Repeated, wasteful multicast –Often repeated responses –Need intelligent caching or handling of multicast packets Service discovery neatly fits this model –Move from our mcast solution to Apple’s Bonjour

Use of Bonjour SRV : query._7ds._udp TXT : columbia TXT : news TXT : new york SRV : query._7ds._udp TXT : deals TXT : times square TXT : weather TXTRecordSetValue() TXTRecordGetValuePtr() “Here is the result for times square” “Here is the result for columbia” Improvement of Querying System

Zeroconf

Zeroconf: Requirements of 7DS local peer-to-peer wireless ad-hoc networks - no DHCP server - no DNS server Service discovery –Getting web-pages, sending s, file transfer with peers, file synchronizing 7DS requires automatic networking configuration of IP addresses and name, and service discovery –Solution: Zeroconf

What is Zeroconf? Zero Configuration Networking (Zeroconf) No Infrastructure –Allocate IP addresses without a DHCP server –Translate between domain names and IP addresses without a DNS Server –Find service without a directory service A simple and reliable way to configure and browse for services in local area networks Bonjour, Avahi, ……

Apple’s Bonjour Apple’s implementation of zero-configuration networking 3 main features –Addressing ( allocating IP addresses to hosts) –Naming (using names to refer to hosts instead of IP addresses) –Service Discovery (finding services on the network automatically) Easy to use API, in C and Java –Multicast DNS, which is how Bonjour handles all aspects of Zeroconf, is done via a separate mDNSd daemon