BonAHA: Service Discovery Framework for Mobile Ad-Hoc Applications

Suman Srinivasan, Arezu Moghadam, Henning Schulzrinne

Internet Real Time Lab,

Columbia University, New York, USA

IEEE CCNC 2009: M1-2 Personal Ad Hoc and Sensor Networks

Topics

• Problem/motivation

• Approach– Service discovery and Bonjour– BonAHA framework

• Demos

• Applications developed

• Related Work

Motivation

• Mobile nodes; highly mobile networks– No infrastructure

• OLPC; mesh networks• New class of applications

– “Ad-hoc/Mobile-P2P applications”– Opportunistic networks

• Applications need to– Be aware of network transitions– State/metadata of nodes in the network

Examples of applications

• Group chat

• File transfer

• File synchronization

• Local multiplayer games

Solution 1: Raw multicast

• Initial solution– “Dumb” multicasting to announce and

get information from peers

Solution 2: Service Discovery

• Looked at writing our own framework for solving this problem

• But, good news:– Service discovery does exactly this– Actually, something very similar

• ZeroConf: Most widely implemented– Apple’s Bonjour, Avahi, …

• Apple’s Bonjour– Still requires a learning curve– Developer has to rewrite code

Problems

• Bonjour API – Three event listeners, five function calls– Have to be completely implemented if an ad-

hoc application wants to announce and listen

• Two other major problems– No internal state maintained by Bonjour for

services, related IP address and TXT records– Resolution can be done only on arrival or exit of

services/nodes

BonAHA

• Aim to create a framework that solves these problems

• Much simpler, and more intuitive, API for ad-hoc applications

• Applications need not maintain state or do “resolution”– BonAHA will maintain state– No need for resolution; all nodes and

metadata are objects

BonAHA• For registration

service = new BService("7ds_location2", "tcp");

service.set("Latitude", lat);service.set("Longitude", lon);service.register();service.setListener(this);

• For network transitions (nodes entering/leaving)– nodeUpdated()– nodeExited()

• No need for maintaining state

register() function

BonAHA framework

Node 2

Node 1

key21 = value21key22 = value22key23 = value23key24 = value24

key11 = value11key12 = value12key13 = value13key14 = value14

[2] node1.get(key13)

[1] node1.register()

[3] data = node1.fileGet( value13);

TXTRecord

DNSRegistration

RegisterListener

serviceRegistered()

DNSSDService

BrowseListener

serviceFound() serviceLost() DNSSDService

ResolveListener

serviceResolved()

DNSSD.resolve()

DNSSD.register()

TXTRecord Host IP

DNSSD.browse()

set()

Bonjour State Diagram

BService

BListener

serviceUpdated()

set() register() setListener()

serviceExited()

BNode

get() getHostName() getHostAddress()

BonAHAState Diagram

Example: LocationFinder

• Very simple, impractical application– Only for providing a quick code sample

• Scenario– Two nodes meet each other– Lack global knowledge of location– Each can find out other’s last location

information and update their own location

Code: LocationFinder

Compare: Bonjour Code

TicTacToe

• BonAHA sample application

• Shows use in– Multi-player games– Mutual awareness

BonAHA Applications

BBS application

• Runs on iPod/iPhone

• Allows users to upload “posts”

• Other users can pick up “posts” and share their own

• Information on events, etc that they are interested in sharing

BonAHA Applications

• BBS Application

BonAHA Applications

Group chat

• Allows users to discover peers in local network and chat

• Rooms can be set up for private chats

BonAHA Applications

File Sharing

• Users can share files with each other by dragging and dropping files onto peers’ computers

• Handles peers entering and leaving network

Related Work

• Proem (2001)– Needs to run on “peerlet engine”– No public documentation of API

• JXTA– Excellent for P2P– Heavyweight for our goals

• Peer2Me– File transfer on Bluetooth

Related Work

• LightPeers– Sep 2007 PhD dissertation (B. Christensen)– Similar model to BonAHA

• “Application”: Each application has its own GUID that identifies it

• “Session”: A group of nodes registered as running the application

– Code• Application app = new Application(appid);• lpconn = new Connection(app);• ses = lpconn.CreateSession();• List<Session> sessions = lpconn.GetSessionList();

Related Work - LightPeers

• Differences with BonAHA– PING packet sent every second to

search for peers• In Bonjour, there is exponential backoff

– No library-daemon interface• LP “server” listens to packets

– Reimplementation of entire architecture (service discovery + framework)

Future Work

• Develop useful applications• Fix some API features

– Allow one BService object to create several instances.E.g.: one node may want to serve HTTP on two ports.

• Perhaps add high-level communications API for simple networking tasks.E.g.: getFile(), notifyPeer(), sendObject()

Conclusion

• New scenario: highly mobile networks without infrastructure

• Require a new class of application – “ad-hoc” or “mobile P2P” apps

• Require a new framework for programming these applications– BonAHA, built on top of ZeroConf

service discovery: a framework towards building such applications

Questions?

Backup Slides

Apple’s Bonjour

• Implementation of Zero Configuration Networking (ZeroConf) by Apple Computer– This is what enables sharing in iTunes,

iChat, etc.

• Implemented on Mac OS, Windows, Linux and some other POSIX platforms– Ported to Windows CE as well

Apple’s Bonjour

• Two main components– mDNS Daemon

• Takes care of all Zeroconf events• Listens to network events (link up, down, …)• Listens to mDNS traffic and keeps track of

all service announcements and requests

– Library (Interfaces for C, Java, …)• Allows applications to announce, browse for

and resolve services

Apple’s Bonjour

• Details: Presented in Fall 2006– http://developer.apple.com/networking/b

onjour/

• Important things to remember– IP address autoconfiguration: Link-local

addressing• Pick random from 169.254/16

– Hostname resolution: mDNS• DNS-like protocol, each host listens on

224.0.0.251, port 5353

Apple’s Bonjour

• Service Discovery: DNS-SD– DNS PTR records– Announcement of form:

ServiceName._http._tcp.local.

– Browsing for _http._tcp.local. gives list of web service instances

– Resolving ServiceName yields hostname, TXT records, etc.

Bonjour API

• Factory class: DNSSD• Interfaces: Callback functions for events

– BrowseListener: Service browsing– ResolveListener: Name Resolution– RegisterListener: Service

Registration– QueryListener: DNS Record

Resolution– DomainListener: Domain Resolution

Bonjour API

• BrowseListener– serviceFound() when services appear– serviceLost() when service leaves

• ResolveListener: – serviceResolved() to get hostname, TXT

records

• RegisterListener: – serviceRegistered() when registration

succeeds (or fails)

Related Work - LightPeers

http://www.daimi.au.dk/~bentor/LightPeers/

TXTRecord

DNSRegistration

RegisterListener

serviceRegistered()

DNSSDService

BrowseListener

serviceFound() serviceLost() DNSSDService

ResolveListener

serviceResolved()

DNSSD.resolve()

DNSSD.register()

TXTRecord Host IP

DNSSD.browse()

set()

Bonjour State Diagram

BService

BListener

serviceUpdated()

set() register() setListener()

serviceExited()

BNode

get() getHostName() getHostAddress()

BonAHAState Diagram