SMS PDU in Android

Generate ECC200 in Android SMS PDU

Figure 11-4

headers to be defined inside a message allows any amount of additional functionality can be built on top of SMS messages This functionality does not always have to be as advanced as graphical messages, however For example, one extremely common use of the User Data Header is to allow multipart SMS messages When a user wishes to send a message that contains more characters than can be held by a single message, a User Data Header is defined that tells the receiving mobile phone that this message will be delivered in multiple parts This multipart message UDH then contains all the information the receiving mobile phone needs to successfully reconstruct the different parts of the message into the one large message the user originally sent Figure 11-4 illustrates a UDH inside an SMS PDU

When SMS was first designed, it was only to send basic text content of a relatively small size As with many technologies, however, it has since progressed far beyond its original design goals Multimedia Messaging Service (MMS) is the next progression in the usage of SMS MMS can send various types of images, audio, and video in addition to text The demand for this functionality arose out of the changing nature of mobile phones themselves As time progressed, mobile phones began to contain more and more functionality, such as the ability to record audio, take pictures, and even record video Once users had this technology in their phones, carriers saw the potential to generate new streams of revenue by allowing users to share their audio and video content with each other, hence the creation of MMS Initially from an introductory high level, MMS can be thought of as fairly similar to SMS For example, consider the typical use case of MMS as shown in Figure 11-5 In this example, Bob wants to send a picture of his new robot to Alice Unlike with SMS however, Alice receives a message notification rather than message content Alice selects

Figure 11-5

to download the message contents to her phone from the carrier s servers Upon successful download, the image and text is displayed to Alice Although it may appear to the user that MMS is almost exactly like SMS, MMS is fundamentally different from SMS From the mobile carrier perspective, MMS requires a far higher level of equipment and support This is illustrated in Figure 11-6, which shows the delivery of an MMS message with more details provided In another example of its additional complexity over SMS, MMS does not use just one technology Rather, several technologies are used throughout the creation and delivery of an MMS message

Figure 11-6

For these reasons, not all carriers implement full support for MMS As discussed, true MMS support should allow users to be able to send any audio, video, or pictures of their choice However, carriers will often limit the functionality allowed on their networks to simple pictures Finally, some carriers do not even truly support MMS but instead fake it by embedding a link to MMS content within a normal SMS The user then visits the carrier s website using the cell phone s web browser

Wireless Application Protocol (WAP)

WAP is a collection of standards developed in order to provide Internet access to cell phones The standards were originally written by the WAP Forum and later by the Open Mobile Alliance (OMA) Both of the groups memberships include equipment vendors WAP is used primarily to provide interactive content such as web browsing as well as to provide carrier-specific information to phones in the background Figure 11-7 shows a phone accessing a WAP site WAP browsers use Wireless Markup Language (WML) rather than HTML There are many similarities between the WAP protocol suite or stack and common IP protocols; Figure 11-8 illustrates some of these similarities Keep in mind that these are not exactly the same but rather close equivalents The lowest level on the WAP stack from Figure 11-8 is described as bearer, which is a protocol that can carry Wireless Datagram Protocol (WDP) The most common bearers are SMS- and IP-based ones This chapter discusses SMS rather than IP bearers WDP is designed to be very similar to User Datagram Protocol (UDP) Traffic is expensive over cellular networks not only in data costs, but transmission costs are also high Battery life is a crucial resource, and as such a UDP-like protocol eliminates the overhead associated with TCP Wireless Session Protocol (WSP) is equivalent to HTTP, in particular HTTP/11 However, in order to save space, the protocol is binary In essence, WSP is a compressed form of HTTP Wireless Application Environment (WAE) carries various markup languages Older implementations (WAP 1x) use WML Newer implementations (WAP 20) use XHTML-MP These markup languages are similar to various nonmobile markup languages for web content