The Main Protocols used by Mobile Phones: SMS EMS MMS WAP.


SMS stands for Short Message Service. It is a technology that enables the sending and receiving of messages between mobile phones. SMS first appeared in Europe in 1992. It was included in the GSM (Global System for Mobile Communications) standards right at the beginning. Later it was ported to wireless technologies like CDMA and TDMA. The GSM and SMS standards were originally developed by ETSI. ETSI is the abbreviation for European Telecommunications Standards Institute. Now the 3GPP (Third Generation Partnership Project) is responsible for the development and maintenance of the GSM and SMS standards. As suggested by the name “Short Message Service”, the data that can be held by an SMS message is very limited. One SMS message can contain at most 140 bytes (1120 bits) of data, so one SMS message can contain up to:

160 characters if 7-bit character encoding is used. (7-bit character encoding is suitable for encoding Latin characters like English alphabets.)

70 characters if 16-bit Unicode UCS2 character encoding is used. (SMS text messages containing non-Latin characters like Chinese characters should use 16-bit character encoding.)

SMS text messaging supports languages internationally. It works fine with all languages supported by Unicode, including Arabic, Chinese, Japanese and Korean. Besides text, SMS messages can also carry binary data. It is possible to send ringtones, pictures, operator logos, wallpapers, animations, business cards (e.g. VCards) and WAP configurations to a mobile phone with SMS messages. One major advantage of SMS is that it is supported by 100% GSM mobile phones. Almost all subscription plans provided by wireless carriers include inexpensive SMS messaging service. Unlike SMS, mobile technologies such as WAP and mobile Java are not supported on many old mobile phone models.

Why use SMS
SMS is a very inexpensive method of communication. 160 characters take up as much room as a one-second voice call. Messages are delivered immediately (or when the phone is turned on). Like e-mail, they can also be reviewed or stored in your phone for as long as you wish. SMS messages can also be sent out to huge groups of people with the single press of a button. SMS also allows for unified messaging. This is where SMS can take on a number of different message formats (including voice mail, e-mail and fax) and allows users to access them from their mobile device.

Concatenated SMS Messages / Long SMS Messages
One drawback of the SMS technology is that one SMS message can only carry a very limited amount of data. To overcome this drawback, an extension called concatenated SMS (also known as long SMS) was developed. A concatenated SMS text message can contain more than 160 English characters. Concatenated SMS works like this: The sender’s mobile phone breaks down a long message into smaller parts and sends each of them as a single SMS message. When these SMS messages reach the destination, the recipient mobile phone will combine them back to one long message. The drawback of concatenated SMS is that it is less widely supported than SMS on wireless devices.


Besides the data size limitation, SMS has another major drawback — an SMS message cannot include rich-media content such as pictures, animations and melodies. EMS (Enhanced Messaging Service) was developed in response to this. It is an application-level extension of SMS. An EMS message can include pictures, animations and melodies. Also, the formatting of the text inside an EMS message is changeable. For example, the message sender can specify whether the text in an EMS message should be displayed in bold or italic, with a large font or a small font. The drawback of EMS is that it is less widely supported than SMS on wireless devices. Also, many EMS-enabled wireless devices only support a subset of the features defined in the EMS specification. A certain EMS feature may be supported on one wireless device but not on the other.


Multimedia Messaging Service (MMS) – sometimes called Multimedia Messaging System – is a communications technology developed by 3GPP (Third Generation Partnership Project) that allows users to exchange multimedia communications between capable mobile phones and other devices. An extension to the Short Message Service (SMS) protocol, MMS defines a way to send and receive, almost instantaneously, wireless messages that include images, audio, and video clips in addition to text. When the technology has been fully developed, it will support the transmission of streaming video. A common current application of MMS messaging is picture messaging (the use of camera phones to take photos for immediate delivery to a mobile recipient). Other possibilities include animations and graphic presentations of stock quotes, sports news, and weather reports.

According to Mobile Streams, MMS will be developed in two separate phases. Based on General Packet Radio Services (GPRS), the currently available MMS is similar to a brief PowerPoint presentation. The second phase of MMS will require a 3G network to enable streaming video. An intermediate technology, Enhanced Messaging Service (EMS) has more capabilities than SMS, but fewer than MMS. Unlike MMS, EMS doesn’t require upgrades to network infrastructures. Unlike SMS and EMS, the size of an MMS message is unlimited, although service providers are likely to impose their own size restrictions.


Wireless application protocol (WAP) is an application environment and a set of communication protocols for wireless devices designed to give manufacturer, vendor, and technology-independent access to the Internet and advanced telephony services. The wireless industry came up with the idea of WAP. The point of this standard was to show internet contents on wireless clients, like mobile phones. Features of WAP are:

  • WAP is an application communication protocol
  • WAP is used to access services and information
  • WAP is inherited from Internet standards
  • WAP is for handheld devices such as mobile phones
  • WAP is a protocol designed for micro browsers
  • WAP enables the creating of web applications for mobile devices.
  • WAP uses the mark-up language WML (not HTML)
  • WML is defined as an XML 1.0 application

What Exactly Is WAP?
In 1997, several companies organized an industry group called the WAP Forum. This group produces the WAP specification, a (long and detailed) series of technical documents that define standards for implementing wireless network applications. Hundreds of industry firms have given strong backing to the WAP Forum, so the technology should become widely adopted, and it is already well-hyped. WAP specifies architecture based on layers that follow the OSI model fairly closely. The WAP model, or stack as it is commonly known, is illustrated below:

Application Layer WAP’s application layer is the Wireless Application Environment (WAE). WAE directly supports WAP application development with Wireless Mark-up Language (WML) instead of HTML and WML Script instead of JavaScript. WAE also includes the Wireless Telephony Application Interface (WTAI, or WTA for short) that provides a programming interface to telephones for initiating calls, sending text messages, and other networking capability. Session Layer WAP’s session layer is the Wireless Session Protocol (WSP).

WSP is the equivalent to HTTP for WAP browsers. WAP involves browsers and servers just like the Web, but HTTP was not a practical choice for WAP because of its relative inefficiency on the wire. WSP conserves precious bandwidth on wireless links; in particular, WSP works with relatively compact binary data where HTTP works mainly with text data. Transaction, Security, and Transport Layers These three protocols can be thought of as “glue layers” in WAP:

Wireless Transaction Protocol (WTP);
Wireless Transaction Layer Security (WTLS);
Wireless Datagram Protocol (WDP).

WTP provides transaction-level services for both reliable and unreliable transports. It prevents duplicate copies of packets from being received by a destination, and it supports retransmission, if necessary, in cases where packets are dropped. In this respect, WTP is analogous to TCP. However, WTP also differs from TCP. WTP is essentially a pared-down TCP that squeezes some extra performance from the network. WTLS provides authentication and encryption functionality analogous to Secure Sockets Layer (SSL) in Web networking. Like SSL, WTLS is optional and used only when the content server requires it.

WDP implements an abstraction layer to lower-level network protocols; it performs functions similar to UDP. WDP is the bottom layer of the WAP stack, but it does not implement physical or data link capability. To build a complete network service, the WAP stack must be implemented on some low-level legacy interface not technically part of the model. These interfaces, called bearer services or bearers, can be IP-based or non-IP based. Bearer Interfaces WAP supports dial-up networking using IP and Point-to-Point Protocol (PPP) as the bearer interface underneath WDP. It also supports Short Message Service (SMS) and General Packet Radio System (GPRS). SMS passes text and binary data between digital phones. GPRS is a relatively new technology that implements faster, “always-on” connections for wireless devices; GPRS actually runs on top of IP.


Architecture of a WAP Gateway WDP:The WAP datagram protocol (WDP) is the transport layer that sends and receives messages via any available bearer network, including SMS, USSD, CSD, CDPD, IS136 packet data, and GPRS. WTLS Wireless transport layer security (WTLS), an optional security layer, has encryption facilities that provide the secure transport service required by many applications, such as e-commerce.

WTP: The WAP transaction protocol (WTP) layer provides transaction support, adding reliability to the datagram service provided by WDP. WSP The WAP session protocol (WSP) layer provides a lightweight session layer to allow efficient exchange of data between applications.

HTTP Interface:The HTTP interface serves to retrieve WAP content from the Internet requested by the mobile device. WAP Applications The way in which mobile wireless devices are used differs dramatically from the way we use PCs. On a PC we may spend hours constantly connected to the Web hunting for information at work or playing complex, immersive games at home. On a
wireless device, we tend to be away from home and “online” for relatively brief and unpredictable periods of time. The wireless industry hopes that WAP devices will become popular for ecommerce applications like online banking in the not-so-distant future. In the short term, it is more likely that useful WAP applications will simply extend the functions of telephone and allow us to answer a phone message with an email, for example. The early WAP applications have featured news feeds, stock quotes, and weather forecasts — hardly compelling content. Significant backlash against the hype and optimism surrounding WAP has certainly occurred as a result of the uncertainly about its future.

The Long-Term Future of WAP:WAP today is tied to the Web mindset in many people’s minds. These people see WAP as just a technology that gives mobile devices access to the Net directly or through gateways. They find it confusing that so many new network protocols, similar but different from the Web protocols, have been developed. However, it is possible that WAP will enable a new and completely different kind of content network in the more distant future.

The WAP was conceived by four companies: Ericsson, Motorola, Nokia, and Unwired Planet (now The Wireless Markup Language (WML) is used to create pages that can be delivered using WAP.