The Mobile Internet

Nour El Kadri

University Of Ottawa

TCP/IP was designed to isolate developers from the idiosyncrasies of the different standards

We need something to do the same for the mobile world since the TCP/IP did not cater for wireless links and mobile devices

Transition standards have been developed to bridge the gap. EX:

WAP

Work of 3GPP on Open Service Access (OSA)

3GPP Mobile Execution Environment (MExE) – Combining WAP with simple Java.

Mobile Internet

TCP/IP on Mobile Networks

• Multiplexing at the Physical and Data Link level– 2G – Circuit switched connections– 2.5G and 3G – Packet switching

• Routing is difficult due to adaptation difficulties in TCP/IP to the demands of mobile communications

• Mobile IP is a variation of IP at the network layer that caters for some of these difficulties

• Mobile IP is an integral part of 3G, but GPRS and CDMA2000 1X support simplified versions of mobile IP

Mobile IP – Routing Packets to Mobile Nodes

• Packets contain headers that identify Destination Addresses

• IP addresses are organized where addresses in the same network have identical prefixes

• As soon as a node or mobile Device like a PDA start moving between networks of different prefixes…..Things start to break down

• Regular IP offers two solutions for dealing with this. Neither is feasible in a mobile environment– Update all routing tables with node-specific entries– Assign new IP addresses to the mobile node

The Remedy – Mobile IP

• It does not require any changes to software or hardware for the existing installed base of IPv4 and routers except those involved in mobility services.

• This is done using:– Tunneling– Care-of-address

• Home agents and mobile agents take care of encapsulating messages and sending them to their intended receipients

TCP: The Wireless Link Requires Special Treatment

• IP is a best-effort service…No guarantee of delivery• TCP makes sure that packets are received, reassembled

and delivered to the application needing them• TCP also addresses flow and congestion control

– In wireline, missing acknowledgement is mostly due to congestion– In mobile wireless, missing acknowledgement is rarely due to

congestion, it is mostly connection drops and transmission errors• Differentiation between the wireless link and the rest of

the network is a partial solution.• GPRS adopts a re-transmission scheme as a solution• Sender and receiver agreements are a problem in

wireless due to intolerable delays

The Mobile Internet: Early Precursors

• Other challenges include developing presentation languages that accommodate:

• The limited screen size• Memory• Power of mobile devices• Limitations of mobile networks

• Even HTTP is not suited for wireless due to its stateless nature

Solutions have been devised:– AT&T PocketNet– Palm.Net-WebClipping– NTT DoCoMo i-Mode

AT&T PocketNet

• Introduced in 1996 by AT&T Wireless• It relies on CDPD which includes a basic TCP/IP protocol

stack• It uses HDML instead of HTML and a special

microbrowser (UP.View) developed by unwired planet, later renamed as Phone.com (acquired by OpenWave)

• HDML introduced the Deck of Cards Metaphor– Devices has tiny screens– Many user applications can be devided into small sets of

interaction (cards)– Send all associated screens (cards) all at once to a mobile

device– HDML evolved into the Wireless Markup Language the

presentation language of WAP

Palm.Net - WebClipping

• A web service introduced by Palm in 1998 for its PDAs• Uses a solution called WebClipping• Webclipping stores the static part of web pages on the

PDA allowing only the dynamic part to be sent over the wireless link

• Several hundred web services have been adapted to run on Palm.Net covering:– Finance– Enterprise applications– Shopping– Information– Entertainment service

NTT DoCoMo i-Mode

• Operates on top of PDC-P packet switched network (known as DoPa) which has a built-in TCP/IP stack

• It relies on cHTML for content presentation designed by Access Corporation

• DoCoMo’s i-Mode servers take care of Authentication and billing for official content providers

• i-Mode vs. WAP competition?• Recent move from cHTML to XHTML Basic which is adopted by

WAP (known as WAP2.0) for replacement of WML• i-Mode started supporting Java based applications through its i-appli

service which relies on Sun’s J2ME providing:– End-to-end security– More interactive applications like games, zoomable maps– Regular traffic updates and similar services

Wireless Application Protocol• WAP Forum founded in 1997 by Phone.com, Ericsson, Nokia and

Motorola• Open standard that is device and bearer-independent• Due t its wide adoption, it achieved the badly needed economies of

scale• Often criticized as too far a deviation from W3C and IETF standards• Developers find it has presentation constraints and question its

security approach• Its limitations are being addressed with time, for instance, WAP 2.0

has support for:– End-to-end security– Color graphics– Animation– Push technology

• WAP collaboration with W3C and IETF led to adoption of XHTML Basic (WML2) and support for TCP and HTTP

WAP Architecture

• WAP is not a Protocol, but a suite of protocols

• It bridges the gap between mobile bearer services and basic Internet Protocols such as:– TCP/IP– HTTP

• This was done through gateways in the early stages

WAP Gateway and Legacy Protocol Stack

• WAP gateway or proxy was used to interface between WAP protocol Stack and the regular internet protocol stack

• WAP content is encoded into a compact binary format before transmission

• WAP gateway decodes it into text interpreted by HTTP and vice versa

• WAP gateway helps improve communication efficiency, authenticates users, provides support for additional billing functionality

Operating without a WAP Gateway

• 2.5G and 3G have a protocol stack that supports the IP protocol. (WAP 2.0, W3C, IETF)

• It is a variation of the TCP and HTTP protocols profiled for operation over a wireless link

• Wireless HTTP provides:– Compression of content– Secure tunneling between Mobile device and web server– In theory, that should eliminate the gateway

• In practice, a gateway is still needed to provide other services like:– Billing– Location-based services– Privacy features– WAP gateway is needed for push services

WAP Legacy Protocol Stacks

Before 2.5G and 3G, we needed the gateway and the legacy of protocol stacks which included:– Wireless Datagram Protocol– Wireless Transport Layer Security– Wireless Transaction Protocol– Wireless Session Protocol– Wireless Application Environment

Wireless Datagram Protocol (WDP)

• Lower level protocol• Sits between bearer services and upper level

protocols in the stack• Depending on the bearer service, its functionality

changes• In cases of built-in IP bearers like GPRS and

UMTS, its functionality is reduced to that of UDP• It simply insures that packets are delivered to

upper layers

Wireless Transport Layer Security

• Designed to provide Privacy, Data Integrity and Authentication between two communicating applications

• It is based on the TLS protocol commonly used over fixed Internet (formerly known SSL)

• TLS operates on top of TCP, thus WTLS has to take on some of that functionality

• Designed to operate over low-bandwidth and high-latency connections

• Security is a burden, so developers have to choose the level of security needed in a cautious way.

• The Gateway poses a security gap.

Wireless Transaction Protocol

• Light-weight transaction-oriented protocol – mostly for thin clients with little memory and power

• Acts as a substitute for TCP while handling some of HTTP functionality

• WTP supports three classes of transaction services

– WTP Class 0: for unreliable message transfer– WTP Class 1: for reliable message delivery without a result

message– WTP Class 2: for reliable message delivery with a result

message confirming reception – useful for banking applications as it allows transaction rollbacks

Wireless Session Protocol

• Provides HTTP/1.1 functionality. It allows for sharing of state between client and server to optimize content transfer

• It allows for Capability Negotiation: level of protocol functionality during a session

• You can resume suspended sessions from where you left

• It allows the management of multiple sessions. EX: from a GPRS session to read e-mail to a UMTS session to join a videoconference.

Wireless Application Environment

• Most visible part of WAP to both users and developers

• It includes– WAP microbrowser– WAP markup and scripting languages

• Important part of WAE is the Wireless Telephony Applications Interface (WTAI). It allows users to access telephony applications from WAP sessions

WAP Protocol Stack for Fast Bearers with Built-in IP

• Wireless Profiled TCP - version of TCP optimized for wireless Environments

• Wireless Profiled TLS – a wireless profile for the TLS protocol found on the wired Internet

• Wireless Profiled HTTP – fully interoperable version of HTTP/1.1 allowing for message body compression and secure tunnels

• Wireless Application Environment – next slide

The Wireless Application Environment

It is the part of WAP that users see. It consists of:– WAP markup and scripting languages– WAP microbrowser– Wireless Telephony Applications Interface

WAP Markup and Scripting Languages

• WML referred to as WML1 or WML1.x• WMLScript is the scripting language• With WAP2.0 we have XHTML Basic which is a subset

of XHTML recommended by W3C• Deck of cards metaphor• WAP allows for Client-Side logic using its WMLScript

which is a bare-bones version of JavaScript. Thus, some processing is done at the client side

• Code reusability is possible due to the import of some code that is written for PCs that can be used for WAP. Thanks to W3C.

WAP Microbrowser

• Sits on the client with a role of interpreting and presenting content

• Content can be written with: legacy WML language, WML Script or XHTML Basic

• Some companies have their own microbrowsers like Ericsson and Nokia

Other Third party microbrowsers available:– Open Wave’s Mobile Browser– AU-System’s browser for PalmOS, Windows CE and

EPOC platforms– Microsoft’s Mobile Explorer– 4thPass KBrowser, runs Sun’s Java KVM

Wireless Telephony Applications Interface

• Contains a list of APIs to invoke applications from WAP browser– Accepting restaurant Ads,– Reservations– Saving telephone numbers to address book

All without having to quit a WAP browser

The WAP Usability Saga

• Deck of Cards Metaphor• Introduction of Persistent Sessions in WSP• Use of WAP User Agent Profiles to better tailor

content• Integration of WAP with telephony applicationsIn spite of this there are complaints:

– Slow connections– Dead ends or sites being down– Sites with poor signposting– Uneven content quality– Small screens

Evolving Application Architectures- How Open is the Mobile Internet?

• Anyone can set up an Internet shop

• Click-through economy

• 3GPP’s Open Service Architecture

• Service Enablers

• Personal Service Environment

Java and MExE

• Device Independence from bearer services – write once run everywhere

• J2ME comes in two different flavors– A connected device configuration– A connected limited device configuration