Standards,Tools& Best Practices
←
→
Page content transcription
If your browser does not render page correctly, please read the page content below
Standards,Tools & Best Practices
Editor: Sumi Helal ■ University of Florida ■ helal@cise.ufl.edu
WAP: Present and Future
Vijay Kumar, Srinivas Parimi, and Dharma P. Agrawal
I n 1997, several wireless-phone man-
ufacturers organized an industry
group called the Wireless Application
HTTP, WAP wireless protocols2–4
require transferring large amounts of
mainly text-based data. The WAP stan-
based on XML.8 It makes optimal use
of small screens, with a built-in scala-
bility from two-line text displays to the
Protocol forum. This group defined the dard consists of two essential elements: full graphic screens on smart phones
WAP specification in the form of a long, an end-to-end application protocol and and communication devices. The Wire-
describes technical document series that an application environment based on the less Application Environment specifica-
defines standards for implementing wire- browser. The application protocol is a tion defines the syntax, variables, and
less-network applications. Hundreds of communication stack embedded in each elements used in a valid WML file.
industries strongly supported the WAP WAP-enabled wireless device (also WML employs the concept of decks and
forum for standardization to help the known as the user agent). The server side cards. Each card is a frame displayed on
technology become widely adopted. defined as a WAP gateway implements the screen. We refer to a logical collec-
Unfortunately, most of the enthusiasm the other end of the protocol, which can tion of interlinked cards as a deck, usu-
surrounding WAP has evaporated owing communicate with any WAP client. ally stored in a single WML file.
to inherently low channel bandwidth, The WAP network structure (see Fig- The second is WMLScript, a client-
increased round-trip delays, and a lack ure 15) sets up a session using these side scripting language used with WML
of security. WAP technology is primitive steps:6,7 that makes WML pages dynamic (simi-
and still evolving, and its future depends lar to what JavaScript9 allows with
on how quickly it can improve the trans- 1. A mobile telephone sends WAP HTML). WMLScript makes minimal
fer rate and effectively enhance its busi- requests to a WAP gateway. demands on memory and CPU usage,
ness model. 2. The gateway, upon receiving a WAP omitting a number of functions that are
request, sends an HTTP request to not required and that are present in other
THE WAP ARCHITECTURE a plain Web server, which provides scripting languages for wireless applica-
In the last few years, WAP has the content through a normal HTTP tions. Regular scripting languages are
emerged as a standard Internet-enabling response (the Web server perceives resource intensive and can’t be used to
wireless protocol and a browser frame- the gateway as a proxy server). display interactive pages on a mobile
work for small, limited-display-capable 3. The gateway converts the HTTP phone. WMLScript is a scaled-down,
devices. WAP allows Internet access to response into a WAP response for simplified script, developed specifically
cell phones, PDAs, and other low-com- the mobile device. to fit the WAP architecture of decks and
putational-power devices. In addition, 4. The microbrowser in the mobile cards. It lets the developer provide inter-
the lightweight WAP protocol has a lay- terminal interprets the response activity in WAP pages without taxing the
ered architecture and is designed to and displays it appropriately. valuable wireless resources.
operate over a variety of wireless serv- The third supporting component is
ices, including Code Division Multiple Wireless Bitmaps. WBMP is the default
Access, Cellular Digital Packet Data, WAP SUPPORTING picture format for WAP. WBMPs are
General Packet Radio Service (GPRS), COMPONENTS uncompressed, monochrome black-
and so on.1 (For more information on WAP technology has three major sup- and-white bitmaps for use in devices
the layered architecture, see the “WAP porting components. The first is the with small screens and narrow band-
Layers” sidebar.) Wireless Markup Language. WML is width connections (see Figure 2). How-
Based on Internet standards such as the WAP equivalent to HTML and is ever, the screen size and bandwidth,
1536-1268/03/$17.00 © 2003 IEEE ■ Published by the IEEE CS and IEEE Communications Society PERVASIVE computing 79STANDARDS, TOOLS & BEST PRACTICES
STANDARDS, TOOLS & BEST PRACTICES
WAP LAYERS
T he WAP protocol stack has five layers:
application, session, transaction, secu-
rity, and transport (see Figure A1). Each layer
agent to the application server. The WTP con-
centrates on transaction services for online
activities such as Web browsing. It is designed
Transport
The Wireless Datagram Protocol transmits
and receives data to and from the user agents.
performs almost the same functions as the to decrease the number of transaction phases The WDP can exchange information with
corresponding layers of the Internet model. that typical wired-oriented protocols require. many types of wireless data carrier technolo-
gies or “bearers.” It effectively hides the dif-
Application Security ferences in bearer technologies from the rest
The application layer consists of the Wireless The Wireless Transport Layer Security imple- of the stack and provides a common interface
Application Environment and user agents. The ments many features to ensure secure data to the upper-layer protocols. Layers can func-
most common type of user agent in the WAP transmissions and to protect the users, the tion independently of the underlying network
architecture is a browser meant to interpret network and service operators, and the func- and the wireless devices.
Wireless Markup Language and WMLScript. tionality of the upper layers of the WAP stack.
REFERENCE
User agents that endeavor to provide services The WTLS provides safe data transmission that
1. D.P. Agrawal and Q.-A. Zeng, Introduction to
beyond those of a browser generally take could support services requiring a high level of Wireless and Mobile Systems, Brooks/Cole Pub-
advantage of the WAP specification’s Wireless security such as mobile e-commerce. lishing, Pacific Grove, Calif., 2003.
Telephony Application features.
Session Internet Wireless Application Protocol
The Wireless Session Protocol presents the
application layer with a way to uniformly HTML Wireless Application Other services and
JavaScript Environment (WAE) applications
receive both “reliable” connection-oriented
and “unreliable” connectionless transmissions.
The WSP facilitates transmission mechanisms Wireless Session Layer
such as HTTP
Wireless Transaction Protocol (WTP)
• Providing HTTP functionality
• Enabling users to participate in long-lived
Transport layer and
data transmission sessions security-secured Wireless Transport Layer Security (WTLS)
• Allowing a server application to determine socket layer
whether a client can support certain proto-
Wireless Datagram Protocol (WDP)
col facilities and configurations (this is TCP/IP
known as “a capability negotiation”) UDP/IP Bearers
SMS USSD CSD IS-136 CDMA CDPD PDC-P Etc.
Transaction
The Wireless Transaction Protocol handles SMS: Short messaging service CDMA: Code Division Multiple Access
requests and responses to and from the user USSD: Unstructured Supplementary Service Data CDPD: Cellular Digital Packet Data
CSD: Circuit Switched Data PDC-P: Personal Digital Cellular Packet
Figure A. The five Wireless Application IS-136: Interim Standard-136
Protocol layers.1
along with limited graphics capabilities, offer major advantages. First, WAP saves Second, there’s no hardware obso-
are WBMP’s major constraints. Recent time and money. A WAP-based applica- lescence. One of the greatest concerns
developments in display technology tion’s ability to send and receive data in for companies with mobile workers is
provide color bitmaps for the latest real time lets companies make field the huge investment in handheld hard-
WAP browsers. changes and coordinate their staff more ware. Companies would be interested
efficiently. Companies can also speed up if the standard could work on legacy
WAP ADVANTAGES and automate their distribution cycle, hardware. This would help them
Many inherent WAP characteristics thus minimizing the required manpower. increase the lifetime of their prior
80 PERVASIVE computing http://computer.org/pervasiveSTANDARDS, TOOLS & BEST PRACTICES
investments in mobile devices.
Finally, WAP allows multiplatform
functionality. Because WML is based
largely on XML,8 little program mod-
ification is required to run WAP-based
applications on traditional Web sites.
IMPORTANT WAP Client WAP Gateway Proxy Origin server
APPLICATIONS
Given that a continuously growing WAP Encoders
WSP request HTTP request CGI
user (URL) and (URL)
percentage of commerce is happening agents decoders Scripts
over the Internet and that the number etc.
Wireless The Internet
of mobile phone subscribers is increas- network
ing, the potential for growth of mobile
WAP Protocol
commerce and hence WAP applications protocol WSP response conversion HTTP response WML
(Binary WML) (WML) WMLScript
is unparalleled. stack
WAP provides an open technology WAP Internet
platform for offering new, innovative protocols protocols
services to the consumer market and a
wireless channel for existing services.
Examples of some such applications are Figure 1. A Wireless Application Protocol network architecture.5
financial trading, buying tickets online,
ordering from restaurants, updating
financial portfolios, conducting bank-
ing transactions (such as transferring
funds between accounts), and compar-
ison shopping.
WAP has also led to sales force and
field service automation. Mobile access
to corporate Intranets lets employees
and business partners access data in a
cost- and time-efficient manner. WAP
has let companies move one step closer (a) (b)
to real-time operations for faster, bet-
ter decision-making and enhanced busi- Figure 2. Two images: (a) normal and (b) Wireless Bitmap.
ness performance.
In addition, WAP’s invention has led
to the development of WAP telephony
applications that add a telephony ele- WAP as a band-aid switched data, we can expect long con-
ment to the basic WAP infrastructure WAP critics say that WAP is only a nection calls for any application that uses
and make existing wireless network temporary fix. We will need it only until interactivity with the Internet or that lets
capabilities available to enhance WAP greater bandwidth in the communication the user select more information.
services. WTAs provide a framework for channel and increased functionality in
integrating wireless data and voice capa- the personal terminal are widely avail- Weak link
bilities to create innovative services. able. GPRS-enabled PDAs, which deliver The WAP gateway must decrypt
28.8 kbps, are already hitting the Euro- secure data coming from a caller using
WAP CRITIQUES pean market. Carriers such as Verizon Wireless Transport Layer Security, and
Just as there is no dearth of WAP and Sprint are building 3G networks then it must re-encrypt the data before
supporters, the number of WAP bash- capable of handling data and video. forwarding it to the bank or credit card
ers is growing. WAP technology is not company (or anyone else receiving it).
flawless, and criticism from leading Wrong bearer services The reverse must also be maintained.
technologists fall into the following WAP is expensive when used with cur- There is a window of vulnerability when
categories. rent bearer technologies. With circuit- the data is momentarily unencrypted.
JANUARY–MARCH 2003 PERVASIVE computing 81STANDARDS, TOOLS & BEST PRACTICES
STANDARDS, TOOLS & BEST PRACTICES
WAP designer’s nightmare with content providers and have essen- which could worsen user experiences. Fat
One of the biggest problems WAP tially made it difficult for content clients face the storage constraints and
developers face is that their applications providers to get any sort of valid return limited processing power of mobile
will likely be rendered in many differ- for their efforts. No true, measurable devices. Applications such as the Virtual
ent ways on different mobile phones. incentives exist to develop WAP con- Private Network (www.vpnc.org) and
Old WAP browsers support HDML tent in the absence of wireless advertis- Virtual Network Connectivity (www.uk.
(Handheld Device Markup Language); ing and other revenue agreements. research.att.com/vnc) have allowed vir-
later browsers support WML. Different Many carriers offer an expensive flat- tual access to desktops from any com-
browsers treat certain tags and com- rate pricing fee to consumers, in addition puter. These technologies rely on the large
mands in different ways, and myriad to subtracting voice minutes for time bandwidth of the wired medium. Much
devices with the same browser also spent on data. This impacts WAP services research has shown that thin-client tech-
function unpredictably. Generally, this in two ways. First, carriers have no effi- nology for desktops might not be a good
lack of coordination among handset cient mechanism to establish fair revenue practice for PC management.10
providers, browsers, emulators, and the sharing with content providers. Second, The latest developments in memory
WAP standard creates a frustrating envi- consumers are historically price-sensitive and storage technologies for handheld
ronment for even the best developers. in the services industry and view WAP as devices are enabling fat-client architec-
too expensive. An example of how a cor- ture by reducing the burden on the
User experience rect business model can help WAP is bandwidth, because local processing
So far, WAP has not lived up to its Telesim, Turkey’s second-largest GSM would eliminate some of the data trans-
promise of being an exciting way to operator. It eliminated its monthly fee for fer done at the remote server. Because
access the Internet. Tradeoffs between WAP usage and experienced a tenfold mobile devices go wherever we go, WAP
functionality, performance, and design growth in its subscribers. technology makes them suitable for the
have dampened user experiences. WAP current storage, memory, and process-
applications with broken links seem to THIN VERSUS FAT CLIENTS ing capabilities of mobile devices. Unless
be the norm, not the exception. Some WAP, also implemented as a thin client, there are astronomical advances in the
people have difficulty just figuring out uses a centralized server to store, fetch, wireless medium to allow larger band-
how to access the microbrowser on their and send data. The meager storage and widths, fat clients seem to be the way to
mobile handset. Furthermore, after wait- low-memory capacity would be suffi- go for future handheld devices.
ing for 30 to 45 seconds to connect, users cient to run varied applications using a
find what looks like a walled garden that thin client. Remote-server-handling capa-
allows access only to certain sites. Access
to options such as “go to other sites” is
cumbersome and frustrating. Inputting a
bility depends on the bandwidth of
the communication media between the
server and the client. On the other hand,
W AP optimists have been quick to
rebut WAP shortcomings. WAP
security has been enhanced in the new
valid WAP URL through the existing fat clients implemented by Java 2 Micro version 2.0, and most shortcomings
numeric keyboard is tedious. Edition and the .NET Compact Frame- have more to do with an inadequate
work make storage and processing more business model than the WAP technol-
Killer applications local than done remotely (for more ogy itself. Also, analysts suggest that if
The hype involving WAP has cen- information on J2ME, see the Jan.–Mar. WAP is incompatible with current tech-
tered on the killer applications, which and Apr.–June 2002 installments of this nologies, GPRS might make it more
were touted to herald a new era of department; for information on .NET- practical.
mobile commerce. However, even after CF, see the July–Sept. 2002 installment). WAP is an application protocol suite
almost five years of WAP development, Fat clients require large memory and designed to function over any bearer ser-
a stable killer application has yet to see storage capacities. vice. This is where GPRS comes into
the light of day. Many have not yet been Each client type has its advantages practice as an ideal bearer for WAP
developed or, if developed, have not and disadvantages. However, it is diffi- resource requirements; its higher trans-
been marketed well enough to catch cult to say which is better, because both fer rates are needed to accommodate
consumers’ attention. are application oriented and the tech- WAP’s unusually complex and frequent
nology is constrained by technological network resource requirements. Fur-
Pricing limitations. Whether wireless messag- thermore, the increased bandwidth will
The pricing of WAP services has been ing should employ a thin or fat client is allow better and more varied applications
problematic for both developers and still debatable. with pictures, video, and sound. Japan
consumers. On the developer side, The obvious disadvantage of a thin and South Korea are already carrying
operators have not shared the wealth client might be its limited feature set, packet data on their networks, and
82 PERVASIVE computing http://computer.org/pervasiveSTANDARDS, TOOLS & BEST PRACTICES
Europe is adhering to the GSM standard 9. D. Flanagan, JavaScript: The Definitive
Guide, 3rd ed., O’Reilly & Associates,
How to Reach Us
with many confirmed GPRS contracts. Sebastopol, Calif., 2001.
WAP technology could bring about
the convergence of mobile communica- 10. P. Lowber, “Thin Client vs. Fat Client Writers
TCO,” research note, Gartner, 2001, For detailed information on submitting
tions and the Internet. With any new www.compaq.co.uk/lifecycle/reports/docs/
technology come risks, bugs, and thinclient.pdf.
articles, write for our Editorial Guidelines
opportunities. With WAP, the opportu- (pervasive@computer.org) or access
nity and adventure definitely outweigh http://computer.org/pervasive/author.htm.
the risks. However, WAP has not lived
up to its lofty expectations, and its Letters to the Editor
growth has taken a beating. In respond- Send letters to
ing to the recent backlash against WAP,
advocates quickly point out that WAP Vijay Kumar is a graduate
Shani Murray, Associate Lead Editor
IEEE Pervasive Computing
exists today in a very primitive form. student in computer engi-
10662 Los Vaqueros Circle
Still, with the introduction of much neering at the University of
Los Alamitos, CA 90720
faster bearer services such as GPRS or Cincinnati. He has joined the
smurray@computer.org
UMTS and a proper consumer-oriented wireless research and devel-
business model, the struggling WAP opment center of Texas
Please provide an email address or
might just get a much-needed lifeline. Instruments in Berlin, Germany. His research inter-
daytime phone number with your letter.
ests include second- and third-generation proto-
cols and mobile and wireless ad hoc networks. He
On the Web
received his BE in electronics and communication
ACKNOWLEDGMENTS Access http://computer.org/pervasive or
from the Regional Engineering College, Allahabad,
We thank Yamini K. Patri of West Virginia University http://dsonline.computer.org for informa-
India. Contact him at k_vijay@hotmail.com.
for providing useful information. tion about IEEE Pervasive Computing.
Srinivas Parimi is pursuing
Subscription Change of Address
his doctoral degree in elec-
REFERENCES Send change-of-address requests
trical engineering, specializ-
for magazine subscriptions to
1. D.P. Agrawal and Q.-A. Zeng, Introduc- ing in MEMS, at the Univer-
address.change@ieee.org. Be sure to
tion to Wireless and Mobile Systems, sity of Cincinnati. He is also
Brooks/Cole Publishing, Pacific Grove, specify IEEE Pervasive Computing.
Calif., 2003. interested in computer net-
works and automation. He received his master’s
2. Wireless Application Protocol (WAP), Int’l Membership Change of Address
in electrical engineering from the University of
Eng. Consortium, www.iec.org/tutorials/ Send change-of-address requests
acrobat/wap.pdf. Cincinnati. Contact him at sparimi@ececs.uc.edu.
for the membership directory to
directory.updates@computer.org.
3. WAP: An Introduction to the Wireless Dharma P. Agrawal is the
Application Protocol, Mobile Lifestreams,
1999, www.totaltele.com/whitepaper/docs/ Ohio Board of Regents Dis-
Missing or Damaged Copies
Moblifstrms_WAP.pdf. tinguished Professor of Com-
If you are missing an issue or you
puter Science and Computer
4. Wireless Application Protocol: The Cor- received a damaged copy, contact
porate Perspective, white paper, Nokia, Engineering at the University
membership@computer.org.
1999, www.nokia.com/corporate/wap/ of Cincinnati. He is the found-
files/whitepaper.pdf. ing director of the Research Center for Distributed
Reprints of Articles
5. Success 4 WAP, white paper, Cisco Sys- and Mobile Computing. His research interests
For price information or to order reprints,
tems, 2001, www.mobilewhitepapers.com/ include energy-efficient routing and information
send email to pervasive@computer.org or
pdf/wap.pdf. retrieval in ad hoc and sensor networks, effective
fax +1 714 821 4010.
6. Yi-Bing Lin and Imrich Chlamtac, Wireless handoff and multicasting in integrated wireless net-
and Mobile Network Architectures, John works, interference analysis in piconets and routing
Wiley & Sons, New York, 2001. Reprint Permission
in a scatternet, use of directional antennas for
To obtain permission to reprint an article,
7. WAP White Paper, Mobileinfo.com, www. enhanced quality of service, and scheduling of peri-
contact William Hagen, IEEE Copyrights and
mobileinfo.com/WAP/model.htm. odic real-time applications. He received his DSc
Trademarks Manager, at whagen@ieee.org.
from the Federal Institute of Technology, Lau-
8. D. Hougland and K. Zafar, Essential WAP
for Web Professionals, Prentice Hall, Upper sanne, Switzerland. Contact him at dpa@ececs.
Saddle River, N.J., 2001. uc.edu.
JANUARY–MARCH 2003 MOBILE AND UBIQUITOUS SYSTEMSYou can also read
