networking and mobile devices. content and goals introductionintroduction application...

Networking and Mobile Networking and Mobile DevicesDevices

Content and goalsContent and goals

• IntroductionIntroduction• Application partitioningApplication partitioning• Concerns in networkingConcerns in networking• Sample techniquesSample techniques

– Web ServicesWeb Services– BluetoothBluetooth

• MIDP Java and web servicesMIDP Java and web services• Symbian OS and BluetoothSymbian OS and Bluetooth• SummarySummary

IntroductionIntroduction

• Fundamentally, mobile devices liberate from the Fundamentally, mobile devices liberate from the restrictions associated with a location -> Physical restrictions associated with a location -> Physical distributiondistribution

• IssuesIssues– ResourcesResources– Transparency (off-line working, cost awareness, energy Transparency (off-line working, cost awareness, energy

consumption, travel-through time, ...)consumption, travel-through time, ...)

• Can be taken as yet another resource whose accessing Can be taken as yet another resource whose accessing can be slowercan be slower– E.g. memoryE.g. memory

• Separate thread often needed for UI and Separate thread often needed for UI and communicationscommunications

Networking SystemNetworking System

Station 1

Station 2

Station 3

transmissions

Adding a ProxyAdding a Proxy

Station 1

Station 2

WirelessStation

Proxy

Fixeddomain

Wirelessdomain

Example Proxy: Wireless CorbaExample Proxy: Wireless Corba

GIOP

GTP

Adaptationand

transport

object

Terminal

GTP

Adaptationand

transport

IIOP

TCP

GIOP

IIOP

TCP

objectCorba invocations

Access bridge Other ORBwireless fixed

Wireless Application ProtocolWireless Application Protocol WAP WAP

Example Proxy: WAPExample Proxy: WAP

WAP device

WAE

WSP

WTP

WTLS

WDP

Bearer

WAP gateway

WSP

WTP

WTLS

WDP

Bearer

Web server

WAE

HTTP

SSL

TCP

IP

HTTP

SSL

TCP

IP

(WAP Stack in Device)(WAP Stack in Device)

Application layer: Wireless application environment (WAE)(includes WML and WMLScript)

Session layer: Wireless session protocol (WSP)

Transaction layer: Wireless transaction protocol (WTP)

Security layer: Wireless transport layer security (WTLS)

Transport layer: Wireless datagram protocol (WDP)

Bearers (SMS, CSD, GPRS,...)

bypassing apps

Infrastructure vs. Ad Hoc Infrastructure vs. Ad Hoc NetworksNetworks

• InfrastructureInfrastructure– Managed structure; control on who is allowed to Managed structure; control on who is allowed to

participateparticipate– Somewhat staticSomewhat static– Commonly relies on e.g. servers and registry Commonly relies on e.g. servers and registry

componentscomponents

• Ad-HocAd-Hoc– Members enter and leave uncontrollablyMembers enter and leave uncontrollably– Dynamic in natureDynamic in nature– Commonly relies on e.g. dynamic service Commonly relies on e.g. dynamic service

discovery and formation rather than serversdiscovery and formation rather than servers

Ad-hoc networkAd-hoc network

A

C

B A

C

B

D

A

D

Stateful vs. Stateless Systems Stateful vs. Stateless Systems

• StatefulStateful– Each station can have its own stateEach station can have its own state– Global state is the combination of all local statesGlobal state is the combination of all local states– Complicates e.g. testingComplicates e.g. testing

• StatelessStateless– No stored stateNo stored state– Usually one controlUsually one control– Eased testingEased testing

• Dilemma: Stateless can implement stateful by Dilemma: Stateless can implement stateful by carrying all state information in transmissionscarrying all state information in transmissions– Serious communication overheadSerious communication overhead– Needed in practice if no support from underlying Needed in practice if no support from underlying

infrastructureinfrastructure

Design patterns for networking Design patterns for networking environment environment

• Use a network wrapperUse a network wrapper

• Consider treating networking features Consider treating networking features similar to resourcessimilar to resources

• When implementing server, keep it When implementing server, keep it separate from clientseparate from client

• Be prepared for loading timesBe prepared for loading times

• Consider proactivenessConsider proactiveness

Program-Oriented Approach Program-Oriented Approach using Client-Server Paradigmusing Client-Server Paradigm

Client 3

Client 1

Client 2

Server 1

Services

Server 2

Services

Client-Server Architecture in a Client-Server Architecture in a Mobile Device Only SystemMobile Device Only System

Device 1

Device 2

Device 3

ServerApp 1

ClientApp 1

ServerApp 2

ClientApp 2

ClientApp 2

ClientApp 2

Browser-based ApproachBrowser-based Approach

• Only requests and replies used, stateless Only requests and replies used, stateless protocol is enoughprotocol is enough– WML, HTTP, XHTML, ...WML, HTTP, XHTML, ...

• Downloading of executables that run on the Downloading of executables that run on the flyfly

• Problems Problems – Convenient use may require redesign of web Convenient use may require redesign of web

systems in any casesystems in any case– Travel-through time can be difficult to hideTravel-through time can be difficult to hide– Proxy?Proxy?

Web Browsing ProxyWeb Browsing Proxy

Computerat home

Web server

Services

Mobiledevice

Wireless access- Screen shots- Link information

Broadband access- HTTP- Java

Telephony or Data Telephony or Data Communications?Communications?

• TelephonyTelephony– SMS, MMS (SMIL)SMS, MMS (SMIL)– Commonly rapid connections (something may be taking Commonly rapid connections (something may be taking

place behind the curtains however)place behind the curtains however)– Network push is okNetwork push is ok

• Data communicationsData communications– GPRSGPRS– Long connection timeLong connection time– How to make a network initated operation?How to make a network initated operation?

• Some issuesSome issues– Cost, ease of use, what is expected by the user, what Cost, ease of use, what is expected by the user, what

facilities are available in the installation base, ...facilities are available in the installation base, ...

Concerns in NetworkingConcerns in Networking

• Network resource managementNetwork resource management– Often visible in software architecture as a dedicated Often visible in software architecture as a dedicated

application moduleapplication module– Connection to e.g. master communications facility?Connection to e.g. master communications facility?

• Finding suitable network componentsFinding suitable network components– Know the addressKnow the address– Centralized repositoriesCentralized repositories– Query protocolsQuery protocols

• Service useService use– Stateless or stateful communications?Stateless or stateful communications?

• Graceful terminationGraceful termination– User initiatedUser initiated– TimeoutsTimeouts

Web ServiceWeb Service

device

UDDI

Web service

servicelookup

WSDLservice

description

serviceuse

Web Service (Cont’d)Web Service (Cont’d)

• Application modelApplication model– No particular model; offers independent servicesNo particular model; offers independent services

• Finding web servicesFinding web services– UDDIUDDI– WS Dynamic DiscoveryWS Dynamic Discovery

• Service useService use– Acts as a service, not as an objectActs as a service, not as an object

• BearersBearers– SOAPSOAP– Bearer independent, practical implementations Bearer independent, practical implementations

commonly use HTTPcommonly use HTTP

BluetoothBluetooth

Physical connection (USB/UART/I2C...)

BT HWHost Controller Interface Driver

Baseband controller

Link manager

BT HOST (Laptop, MCU)

L2CAP

Host Controller Interface Driver

RFCOMM SDP

app1

app2

PPP

UDP/TCPIP

Bluetooth (Cont’d)Bluetooth (Cont’d)

• Application modelApplication model– No particular model; offers independent servicesNo particular model; offers independent services– Bluetooth profiles define different applicationsBluetooth profiles define different applications

• Finding BT servicesFinding BT services– SDPSDP

• Service useService use– RFCOMM, serial port emulating protocol, can be used as a RFCOMM, serial port emulating protocol, can be used as a

bearer for more complex protocolsbearer for more complex protocols– Other protocols for using certain standardized services (e.g. Other protocols for using certain standardized services (e.g.

OBEX)OBEX)

• BearersBearers– Own radio technology (frequency 2,4000-2,4835GHz)Own radio technology (frequency 2,4000-2,4835GHz)

MIDP Java and Web ServicesMIDP Java and Web Services

LocalApplication

Stub

Service ProviderInterface

Local Client

1

2

3

4 Network

Device

RemoteServices

1. Application calls stub2. Stub calls WB via SPI3. SPI opens a connection to remote WS4. Remote computer serves the request

APIs and ToolsAPIs and Tools

• Java API for XML processing (JAXP)Java API for XML processing (JAXP)– Non-validating parser intended to parse incoming Non-validating parser intended to parse incoming

XML documentsXML documents

• Java API for XML-based RPC (JAX-RPC)Java API for XML-based RPC (JAX-RPC)– Implementation of RPCImplementation of RPC

• Service Provider Interface (SPI)Service Provider Interface (SPI)– Stub generation in a compatible fashionStub generation in a compatible fashion

• Stub GeneratorStub Generator– Generation of client-side proxy that can be called Generation of client-side proxy that can be called

by the application to make calls to WSby the application to make calls to WS

Some Other Available TechniquesSome Other Available Techniques

• BluetoothBluetooth

• MessagingMessaging

• Telephony featuresTelephony features

• HTTP and browsing related featuresHTTP and browsing related features

• Plain data communications using e.g. Plain data communications using e.g. sockets or serial portsockets or serial port

Symbian Bluetooth FacilitiesSymbian Bluetooth Facilities

• Service DatabaseService Database– Hosts information that can be used by other devicesHosts information that can be used by other devices– Used via Database Server API (RSdp), actual database Used via Database Server API (RSdp), actual database

characterized by RSdpDatabasecharacterized by RSdpDatabase

• Service DiscoveryService Discovery– Used to find devices, services and service attributesUsed to find devices, services and service attributes– Discovery agent (CSdpAgent) for configuring and starting Discovery agent (CSdpAgent) for configuring and starting

the searchthe search– Notifier interface (MSdpAgentNotifier) for callbacksNotifier interface (MSdpAgentNotifier) for callbacks

• Service useService use– E.g. socket communicationE.g. socket communication

Some Other Available TechniquesSome Other Available Techniques

• MessagingMessaging– Email, SMS, MMS (targeted to human)Email, SMS, MMS (targeted to human)– BIO (targeted to device)BIO (targeted to device)– FaxFax

• Browsing protocols (e.g. HTTP, WAP)Browsing protocols (e.g. HTTP, WAP)• TelephonyTelephony• FTP and Telnet over a data connectionFTP and Telnet over a data connection• GPRS, Bluetooth, Infrared, USBGPRS, Bluetooth, Infrared, USB

SummarySummary

• Network resources form yet another layer of Network resources form yet another layer of facilities and resources for applicationsfacilities and resources for applications– Longish travel-through timesLongish travel-through times– Restricted support for handovers can sometimes Restricted support for handovers can sometimes

cause problems (e.g. IP address change)cause problems (e.g. IP address change)– Firewalls, etc.Firewalls, etc.

• Two-thread patternTwo-thread pattern– One for user, one for networkOne for user, one for network

• Stateless vs. stateful applicationsStateless vs. stateful applications

networking and mobile devices. content and goals introductionintroduction application...

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