Mobility-EnhancedNetwork Services

Todd Hodes, Randy KatzComputer Science Division

University of California, Berkeley

http://www.cs.berkeley.edu

Scenario

• Enter campus, check PDA for list of services– e.g., obtain campus map, check building location

Soda Hall

Current Cell

Enter Soda Hall

• Available services change– e.g., Current map changes

“foyer services”

Move to Auditorium

• See additional services presented– e.g., Obtain VCR and A/V switching controls

– e.g.., Existing light switch UI widget remapped to local lights

“foyer services”

“auditorium services”

Print Notes

• Select printer; location noted on current map• Print & retrieve file, return to auditorium

Location-based Services

• Maps + Coarse-grained location tracking• Printers, lights, audio/video equipment• DNS, NTP• many others...

Outline

• Requirements• Architecture

– Location & Scope

– Services as Partitioned Application Components

• Prototype Applications• Summary• Future Work

Requirements

2) Remote-Controllable Devices / Apps

3) Service Discovery

4) Transducers between objects and clients

clients objects

2

4

3?1) Non-intrusive

Mobile Devices

1

1) Client Devices

• Use of small mobile devices – promotes goal of “non-intrusive” usage

– allows users to interact with their “usual” device rather a “new” (local) one

Remote Control

This? Or this?

2) Controllable Objects

• Define and create specific API for control of apps

• Expose control interface over the network while separating/minimizing UI assumptions

RS

-232

IP

computer

device

control interfacesaccessiblevia IP

Example Devices: UCB CoLab

TV monitor,Camera, &Speaker

sets

Computers

Serial muxLiveBoard

A / V switch

Mic amp

Echo Canceller

Scan Converters

Not shown: VCR, power control, ON-AIR sign, WaveLAN base station, ...

Receiver

3) Service Discovery

• Advertise, register, & query– Scalable management of hierarchy of available services

– Scoping, rate-limiting for wide-area

• Naming

?

Other Services

. . . . . .

ServiceDiscoveryService

query register

clients objects

advertise

Scoped Discovery Bootstrap

• Mobility beaconing is an announce/listen protocol – unify with a service location announce/listen protocol– announced data is location information

• Advertisements (push) vs. queries (pull)– push: user anonymity, power, traffic

• Contrast announce/listen with lookup-based schemes– adaptive scoping/forwarding (vs. DHCP)

– no root servers (vs. DNS)

– granularity varies with subnets, not area; no additional hardware required if connectivity assumed (vs. GPS)

(header) SIP IP addr port ticket application-specific payload …

beacon packets

Scoping Heuristics

• Tickets included in scoped beacons• For local per-service access

– Without ticket, services are inaccessible

• For local service directory (cache) access– Without a received beacon, contents (and existence)

unknown

request + ticket(scoped) beacon

with ticket

4) Transducing Interfaces

• Map between object and client interfaces at application proxy– remap endpoints & data types, aggregate/subset, compose

• Exploit:– COM/Java Beans-style introspection to discover objects’

interface definitions or explicit Interface Specifications

– exposed indirection between client app and device (control protocol) to vary UI

ApplicationProxyClient DeviceDevice

Proxy

RS-232Wired IPWireless

On-the-fly Transduction

• Utilize interface specification for on-the-fly UI generation/modification

• Still can use existing client-specific UI code

ApplicationProxy

Client DeviceDeviceProxy RS-232Wired IPWireless

GenerationProcess

Control Interface and/or

Existing UI Code

Original or Generated UI

Remapping

• Client UI data type to that expected by control interface

• Current interface widget(s) to new servers

• Control messages to other control messages

0.0 1.00.0 1.00.5

on

off

(enumerated)

(real)

(boolean)

Aggregate or Subset

• Create custom UIs that can use a portion of the functionality from one or more control interfaces

• controllable objects/servers remain independent

AggregateInterfaceDefinitions

ApplicationProxyClient DevicesDevice

Proxies

Compose

• Compose device/server interaction behind unified interface

• Create complex behaviors from independent controllable objects/servers

AggregateInterfaceDefinitions

ApplicationProxyClient DevicesDevice

Proxies

Application Interfaces Summary

• Allow multiple possible interfaces– Match heterogeneity in client devices

– Match differences in available sevices

– Mach per-user variations to suit differing usage models

• Build complex behaviors from independent components– Transparent widget remapping of data type and endpoints

– Feature subsets & aggregates

– Composition

Soda 405 Testbed

ServiceDiscovery

Service

Service Interaction Client

Monolithic A/V controller

Screenshots

Lights

Map with Exported Object Locations

Screenshots (cont.)

Screenshots (cont.)

Camera Control

Audio / Video Switching

Screenshots (cont.)

Video Monitor Switching (RVIC client & server)

Detailed Example: RVIC

• “Remote-controlled VIC”– Removes the UI from the monitor, places it in the user’s

hand• vic’s UI overhead is useless if not used at a desktop

– Reduces vic’s video window configuration complexity by supporting “standard configurations”

• Messaging style:– idempotent, string-based

– use announce/listen for reliability, eventual consistency

RVIC Messages

• RoomServer Messages:• Get SessionList [scope attribute]

• Get MonitorList [scope attribute]

• Get SourcesList <session>

• InitMonitor <monitor>

• Get RoomPresets

• InitRoom <preset>

• RvicServer Messages:• Get MonitorConfigs

• Set MonitorConfig <configSpec>

• Set VideoWindow <windowSpec> <source>

RVIC Message Data

• [scope attribute] :– from Service Directory bootstrap beacon

• address/port + ticket

– or hierarchical scope attribute string for conversion to addr/port• “…/Berkeley Campus/Soda Hall/326 Soda” (TBD)

• <session> : SDP session name

• <windowSpec> : integer window number, with windows ordered from top to bottom then left to right

• <source> : a CNAME of a session source

Detailed Example: RVIC (cont.)

• Request rate and Consistency update scaling:– Eventual consistency via announce/listen

– Exposes basic tradeoff in latency/bandwidth• update state on each action: minimize latency

• rate-limit updates via timers and population estimation (a la SDP): tight bandwidth control

• Multi-user policies atop mechanism:– “Free-for-all:” no locking

– Dedicated controller: coarse locking

– Rotating controller: fine-grained locking

– Voting: no locking, but latency issues (c.f., SCUBA)

Summary

• IP Dial Tone isn’t enough– Deploy services, provide seamless access

• Embed location information into data networks• Variable application interfaces

– discover interfaces, move GUIs

– transduce to reduce need for a priori interfaces

• Used by instructor and students to control an augmented classroom (UCB CoLab)

An architecture and prototype system for composable mobile services

Continuing Work

• MASH collaboration laboratory (326 Soda)– MBone video and audio

– Conference control elements

• Pilot PDA + Metricom interface implementation• User Interfaces (with J. Landay, M. Newman)

– Presentation of controls

– Behavior specification

– Reconciliation of conflicting behaviors

• Extend discovery beyond local-area– hierarchy, scoping, union/intersection

Related Work

• Mobile IP, Overlay Networking• Service Location Protocol• PARCTab, Active Badges• Application Partitioning (Rover, Wit, …)• Proxies/Gateways• DHTML, Universal Remote Controls• Location-based applications (Mobisaic, …)• Distributed object systems (CORBA, DCE, …)

Device Mobility

• Mobile IP, Overlays

Composing

• Create complex behaviors– From independent controllable objects/servers

– UNIX pipe / HTTP proxy model

– Exploits exposed application interface definition and indirection

– Remap an RPC to multiple RPCs on-the-fly

ApplicationProxyClient DeviceDevice

Proxy

DeviceDeviceProxy

InterfaceDefinition