13.6 Relation to I-Mode

Although the problem solved by WAP and I-Mode is the same, the approach taken is different. WAP is a product of industry initiative to develop an open standard for Web data transfers over various radio links. I-Mode solved a problem by use of nonstandard solutions specific to network architectures applicable to NTT DoCoMo. One of the aspects of such differences is in the use of markup language. I-Mode uses compact HTML (cHTML), and WAP uses WML.

Nevertheless, I-Mode has undoubtedly been one of the most successful wireless Web services offered by NTT DoCoMo. The success of I-Mode is evident from the subscription base of 32 million customers in Japan alone in early 2002. It was first offered in February 1999, and provides e-mail, banking, entertainment, and Web browsing services for mobile phones.

13.6.1 I-Mode Network Architecture

Figure 13-7 shows the network architecture for I-Mode. Similarities with WAP architectures are evident in the model with the introduction of the I-Mode proxy server to handle user requests over the radio. Content providers supply I-Mode service directly or through the I-Mode server. The architecture also includes support for corporate customers to access enterprise private data through the I-Mode network with the help of firewall functions.

Figure 13-7. I-Mode architecture.

13.6.2 I-Mode Business Objectives

One of the drivers of the I-Mode is to increase operator revenues for DoCoMo. I-Mode provides architecture for DoCoMo to provide network capabilities for I-Mode services, but the actual content is provided by third-party service providers. Figure 13-8 shows the business model for I-Mode. The subscriber pays the subscription charges and the content charges based on the amount of information used. The content provider collects the charges from DoCoMo and at the same time provides commissions for network services and resources used.

Figure 13-8. I-Mode business model.

13.6.3 I-Mode Protocol Stack

The I-mode protocol stack is shown in Figure 13-9. I-Mode uses the PDC (personal digital cellular) packet bearer for all I-Mode services. Mobile node communications to M-PGW (message packet gateway) module utilize the transport layer (TL) functions. M-PGW translates the TL packets to the TCP packets within the network before forwarding the messages to the I-Mode server. TL packets are more efficient than TCP packets due to smaller overhead and supports basic functions like error detection, response confirmation, and data piggybacking. TL has functions similar to the WTP layer in the WAP network but may be simpler due to simpler HTTP functions.

Figure 13-9. I-Mode protocol stack.

The AL (application layer) protocol is used between the mobile device and the I-Mode servers or the application servers for sending and receiving the content data. AL has smaller functions than the WAE framework but provides similar functions such as push and pull mechanisms.

13.6.4 I-Mode Security

Security is an important feature for I-mode users and content providers offering banking, shopping, and other transaction services to ensure the authentication, data validity, and non- repudiation for accounting reasons. Although the underlying radio protocols are secure, providing an end-to-end, common security protocol and algorithms across different I-mode terminals, I-mode servers and the content servers has been a challenging task for DoCoMo. The I-mode terminals and the content servers make use of the Secure Sockets Layer (SSL) to offer the security features.

SSL provides authentication mechanisms by the use of certifications as specified by ITU Recommendation X.509. The public key cryptosystem uses a

A primer on cHTML and XHTML

cHTML, like WML, is a markup language that was designed and developed by Access Company, Ltd. for small handheld devices and mobile phones and submitted to W3CM in 1998 to meet the requirements of devices with limited battery power, display area, computing, and memory resources. It provides a subset or a compact version of standardized Hypertext Markup Language (HTML) 2.0, 3.2, and 4.0 versions as defined by W3C recommendations. The main differences from the full-fledged HTML version are due to lack of support for some image types, backgrounds, tables, frames , a lot of fonts other than basic ones, and style sheets. JPEG image compression is not supported, but GIF images are supported. Features like scrolling and cursor movements are not supported since the cHTML pages are expected to fit within the small display screens. But navigation can be done by use of four buttons : cursor backward, cursor forward, select, and back/stop.

The benefit of backward compatibility with HTML ensures that the devices using cHTML can connect to the WWW while still using the knowledge and authoring tools already available for HTML. The following figure shows an example of a cHTML page. Although cHTML has been popular for I-Mode services, cHTML will probably be replaced by basic versions of Extensible Hypertext Markup Language (XHTML). The figure shows the markup language family tree.

cHTML and WML, developed by OpenWave Systems, have taken separate routes, resulting in a lack of easy content portability. The founders of WML and cHTML have agreed on a common XHTML definition. XHTML is a hybrid between HTML and XML providing a more robust mechanism for universal mobile Internet communications understood by all devices.

public key/private key duo to verify the authenticity by being able to decrypt only by use of the public key. SSL also verifies if the certificate data have been tampered with, by calculating the message digest of the certificate data by use of the one-way hash function and by verifying the results with the decrypted signature part.

13.6.5 I-Mode Evolution ”FOMA

Japan was the first nation to experience 3G cellular services with WCDMA. 3G UMTS systems have provided significant improvements from the 2G networks in terms of the supported radio bandwidth capabilities, and Japan was eager to adopt the 3G UMTS standard due to a need for higher-bandwidth applications on the packet data network. DoCoMo uses the term FOMA to market the 3G circuit services and packet services. I-Mode services in FOMA are improvised to support video distribution services, music distribution services, and other high-bandwidth applications. Future versions of I-Mode will use WAP 2.0 specifications described in the following section.