Mobile web services are referred to the use of web services on a mobile device, such as mobile phones, handheld computers, PDA and so on, to provide access to web content anywhere and anytime. With the increasing speed of the cellular networks into 3G communications, the growing hardware technology in mobile smart phones, and the popularity of mobile operating systems like Google Androids, requests for mobile web services had been highly demanded into mobile phones.
To use mobile web services, a wireless connection is required to connect the mobile devices and the internet to request the web services. The mobile device will play as the role of both 'router' and 'PC' to retrieve information and perform the instructions. Example: We could place reservation on a movie, use e-money to pay for cinema tickets, by using only our mobile phones.
In common web services, we often use XML language. A mobile web service is also using the same language, with the help of WML (wireless markup language) to convey information to the mobile devices. With the help of XML that holds and WML to show the contents, we also need to have a wireless connection between these devices, which is using WAP architecture.
On the next topic, we will further discuss on the mobile web services.
Discussion
The major concept of wireless mobility is to allow users to have access 'anytime and anywhere', which makes mobile network so popular with this concept. With the growth of mobile networks (3G as an example), many categories of mobile web services were made, example: weather reports, traffic reports, movie reservations, mobile shopping, email, and so on.
Access to these services is normally performed through web browser, which is done commonly on the wired networks. In the internet model, the transport layer is responsible to fetch the information to the end-users, but because it has its limitations in displaying the actual contents the mobile devices, many of the information were not able to deliver to the end-users.
However, according to Ariel Pashtan (2005), mobile operators have made themselves as a platform provider other than just giving access to wireless network. A mobile user access the functionalities via web services are offered by content providers. Depends on the services they offer, some service charges are paid to the content providers. Besides, even if these services are offered to end user, a mobile device that does not have the functionality to support the data transmission is not a complete idea. To overcome this problem, example: Maxis offered the iPhone4, which has the capability of accessing rich contents of the web services, alongside with data plan packages, to allow customers to use various categories of mobile services without concerning of the compatibility.
Below figure shows the relationship between end users, mobile operator, and content provider:
Figure 1 - Relationship between end user, mobile operator and content provider
As we study the figure, we can identify some of the important elements that are in used in a wireless environment. In this figure, end-user (client) that owns a mobile device (PDA/mobile phone) are communicating with the content provider that owns an application server, through a protocol of their registered mobile operator network. An application server usually acts as a service directory, which make the discovery of a service requested by the client. Then, it will send the requested content to the client.
In wireless internet environment, bandwidth limitations and noisy environment is often the problem that leads to high latency. To communicate in the wireless network, the Wireless Application Protocol (WAP) is commonly used. It specifies the standard for information presentation and delivery over mobile devices, such as communication protocols (example: TCP/IP), and presentation languages (example: WML).
As shown in WAP Architecture Version 12-July-2001 (2001), each WAP architecture layers provides their own unique functions like the OSI model, they are bearer networks (protocols), transport services (interface between wireless bearer and WAP layers), transfer services (transfer information between network devices), session (establish connection), application framework (content specification and presentation language), security services (data integrity, authentication, privacy protection and others), and service discovery (service lookup, navigation).
HTTP protocol and SOAP protocol plays a fairly important role to retrieve information and contents. One of the benefits of using HTTP protocol is it can enable the multimedia contents to be displayed on the mobile devices, while SOAP is beneficial when both platforms are different, which means that it doesn't matter that both end devices are using different operating systems to functions its web services. 1 of the example software platform that supports SOAP is Java 2 Platform Micro-Edition for mobile devices, which gives the support for web services to be used on mobile services. (Ariel Pashtan, 2005)
After the content is fetched through the protocols, we often view the content with a micro-browser (web browser for mobile devices). Some popular browsers like Opera and Safari, was designed to enable the contents to display on small screens with desktop-style browsing capability. These browsers will render and reformat the presentation of the content to fit in the mobile device's screen. (Ariel Pashtan, 2005)
