3G Multimedia Messaging Service (MMS)
3G Multimedia Messaging Service (MMS)
By: Ian Moraes
Jun. 7, 2001 02:09 PM
3G is not yet fully established, but the promise of increased bandwidth and greater speed has encouraged the development of more sophisticated wireless applications that can use this higher capacity.
Today's mobile phones are used primarily for their voice capabilities such as making and receiving calls and checking voice mail. Models that enable users to do more, such as manage e-mail or surf the Web, are available, but they lack rich multimedia features such as enhanced graphics, video, and audio, and have limited bandwidth.
Current wireless networks or second generation (2G) networks that use disparate technologies such as Global System for Mobile Communication (GSM), Code Division Multiple Access (CDMA), and Personal Digital Cellular (PDC) are primarily designed for voice communication, but can be used to support a limited amount of data. The next generation of wireless networks, commonly known as 3G, promises significantly increased bandwidth and speed using standards such as wideband CDMA (WCDMA) and cdma2000. The specified 3G system data rates range from 144 Kbps to 2Mbps depending on user mobility factors such as whether the call is made from a rural/urban, indoor/outdoor or high-mobility/low-mobility environment. This compares with 2G system rates of between 9.6 and 19.2 Kbps. However, these new 3G systems will not be rolled out all at once for a number of reasons, such as the need for new licenses and upgrading of network and terminal equipment.
An interim step between 2G and 3G networks is the so-called 2.5G networks that use technologies such as General Packet Radio Service (GPRS) and Enhanced Data Rates for Global Evolution (EDGE). GPRS is a packet-switched standard that can offer speeds of up to 115 Kbps. EDGE is also a packet-switched standard that can offer data speeds of up to 384 Kbps. Although the commitment to providing higher bandwidths has been made, there is considerable discussion in the industry as to the actual data rates, migration paths, and adoption schedules of these new standards. Thus you can expect 2G, 2.5G, and 3G systems to coexist until 3G systems are firmly established.
The promise of increased bandwidth has encouraged the development of more sophisticated wireless applications that can use this higher capacity. One such emerging messaging-related mobile application is the Third Generation Partnership Project's (3GPP) Multimedia Messaging Service (MMS). The purpose of this article is to introduce you to this nascent technical specification and explore the architectural components and technologies of the 3GPP's Multimedia Messaging Service.
MMS offers users with a MMS 3G device or multimedia terminal (MMT) a number of exciting and useful applications. It's anticipated that 3G devices will possess more memory and processing power and even be equipped with a camera to take snapshots that can then be sent as part of a multimedia message. For example, if you're on vacation, you could take a snapshot with your 3G device and send the postcard to a friend with an audio note from you. Another example is that if you're out of town and find a rare antique at a store, you could send a video of the item back to your spouse to peruse on her MMT before purchasing it.
In order to support these types of new applications, changes will be required to existing architectures and system components. These changes are discussed in the following sections by exploring the concept of a multimedia message and the components of the MMS architecture. It's important to mention that although new architectural components, technologies and devices are involved in MMS, it's a goal of MMS to support and extend existing messaging standards. For example, Wireless Application Protocol (WAP) and Internet standards provide MMS with significant support in terms of underlying protocols and service specifications. You'll recognize a number of existing Internet, WAP, and XML standards as they're discussed in this article.
These different types of multimedia content are structured in a multimedia message as a Multipurpose Internet Mail Extension (MIME) multipart format. MIME is used in current Internet e-mail messaging for managing attachments. MIME builds on the Standard Mail Transport Protocol (SMTP), the common Internet mail protocol for sending messages, by allowing new types of content such as audio, video, and images to be included in a message. It accomplishes this by defining new header fields such as MIME-Version and Content-Type and message structures that can contain multiple objects. For example, if a message was composed of a JPEG image, a Content-Type header field set to "Image/Jpeg" would be present in the message.
For a multimedia message, the multimedia message header information is contained in a message part and the proposed content type for this part is application/mmsheader. The multimedia message content such as images or audio clips are represented as standard MIME parts. The details of how a message is presented in a synchronized manner are also described in a separate MIME part. For applications that are not capable of rendering multimedia messages, this presentation MIME part is shown as another attachment of the message. To ensure interoperability between different networks and terminals, MMS specifies a minimum set of formats or codecs for audio, video, and image content. These are shown in Table 1.
Most of these specified MMS formats should be familiar to those who have developed Internet messaging systems. For those not familiar with AMR, Adaptive Multi-Rate (AMR) is a speech codec formalized by the European Telecommunications Standards Institute (ETSI). AMR supports eight different speech coding modes with bit rates ranging from 4.75 to 12.2 Kbps using a sampling rate of 8000Hz. For storing AMR data in a MIME multipart, the MIME type/subtype, "audio/AMR", has been proposed. H.263 is a video codec standardized by the ITU that allows video to be transmitted at low bit rates such as those found in wireless networks.
MMS Architectural Components
MMS User Agent
An MMS User Agent can also perform security-related functions such as signing, encryption, and decryption of a multimedia message. On a related note, the 3G User Services Identity Module (USIM) can be used to authenticate a user. It is implemented as a removable card that can be used with a 3G device. (More information on 3G security can be obtained from the resources at the end of this article.)
In addition to sending and receiving messages, the MMS Relay can forward messages, convert message content from one format to another, send and receive message notifications, and negotiate terminal capabilities. The MMS Relay can also filter messages based on user-specified preferences. The MMS Relay is also responsible for generating charging data when sending or receiving multimedia messages based on factors such as roaming and the types, lengths, and numbers of messages sent or received.
A MMS Relay also provides support for the Virtual Home Environment (VHE). The VHE enables a user to be presented with a consistent set of services, personalization, and user interface customization irrespective of the specific network and device being used. That is, whether a user is in the office, at home, or in a different city, there will be a common look and feel to his or her service environment. VHE provides a user with a personal service environment that's defined in terms of one or more user profiles. A user profile can contain user interface-related preferences such as terminal settings. To maximize the applicability of user profiles to a wide variety of terminals, you should pursue a standard format for MMT configuration such as W3C's Composite Capabilities/Preferences Profile (CC/PP). CC/PP provides a RDF-based vocabulary for expressing user agent profile's capabilities and specified user's preferences. Resource Description Framework (RDF) is an XML application that facilitates the encoding, exchange, and reuse of structured metadata.
To support VHE and other functions, the MMS Relay interfaces with a number of different components such as MMS Servers, WAP Gateways, Short Message Service Center (SMSC), Fax gateways, or proprietary voice message stores. For example, the MMS Relay can communicate with a WAP Gateway for exchanging multimedia messages with a MMT. The MMS Relay is considered an origin server in the WAP architectural framework. When receiving a message from a MMT, the message would be transported using WSP from the MMT to the WAP Gateway and HTTP from the WAP Gateway to the MMS Relay. Alternatively, the MMS Relay can push a notification to a MMS User Agent using the WAP Push Access Protocol (PAP). The notification is then sent from the WAP Gateway to the actual device using WAP Push Over the Air (OTA) Protocol. PAP works by sending XML messages through an existing application-level protocol such as HTTP (an HTTP POST method can be called to send a notification). A type of WAP notification is the WAP Service Indication (SI) content type. The SI content type is an XML application representing an asynchronous event that's pushed over PAP. The SI is composed of a short message such as "you have a new multimedia message" and a URI of a service such as a MMS service that's called if the user acts on the notification.
Using WAP, a MMS Relay can be apprised of a WAP device's User Agent Profile (UAProf). UAProf is a WAP framework for describing hardware, software, and application preferences of devices. UAProf, also known as Capabilities and Preferences Information (CPI), uses the CC/PP model and intends to be interoperable with it. UAProf enables the exchange of CPI between WAP devices, intermediate network elements, and the WAP origin server. UAProf defines a RDF-based vocabulary that pertains to such items as display size, WAP browser version, operating system version, and supported content types. The MMS Relay can use this profile to adjust the actual message content delivered to a MMT to account for a WAP device's profile.
MMS User Databases
Architectural Illustration of Sending a Multimedia Message
Suppose that while on a Caribbean vacation, MMS User A uses her MMT to take a picture and record the background sounds of Caribbean music to accompany the picture. MMS User A then sends this multimedia message to another MMS User. To facilitate this discussion, and for illustrative purposes, a number of assumptions have been made regarding the connections, service, and transport protocols between MMS architectural components. The architectural flow of this use case is shown in Figure 3.
This discussion provided you with a vendor-agnostic overview of the enterprise system infrastructure, components, and standards needed to support the Multimedia Messaging Service as currently defined by 3GPP. The pervasive use of current Internet, WAP, and XML standards was illustrated in this presentation of the 3G MMS architecture. You can obtain more details on these and other related multimedia messaging standards and technologies from the Resources section in this article.
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