Technical characteristics in GSM
- According to abbreviationfinder, MMS messages are a new extension of mobile messaging to include, initially, real images and sounds, later videos and in the future virtually any type of content that can be displayed on a mobile phone. In addition, the standard does not define a maximum size limitation, which is a great difference with respect to SMS messages (which admit a maximum of 160 7-bit characters per message), although many operators limit their maximum size for practical reasons.
- In principle, the MMS standard is independent of the type of transport and mobile network used and only defines a content synchronization system (SMIL) and a message encapsulation mode. Depending on the type of network, a method of alerting the user terminal when there are new messages and a transport path on the radio network is used, which do not have to be the same in all networks. This allows mobile users of different types of networks to send multimedia messages without problems, since the final standard used for transport does not matter.
- In GSM networks, GPRS is normally used for its transport on the radio interface, and the user terminal is warned of incoming messages by means of a special SMS with a link to an Internet address where the message is located, called a WAP Push message.. Many terminals automatically classify this incoming SMS as a multimedia message, and download the content automatically and transparently for the user.
- In addition, for the correct management of messages it is necessary to attach a new message center to the GSM network architecture: it is the MMSC or multimedia message management center (Multimedia Message Service Center, analogous to the SMSC of SMS text messages).
- In UMTS / 3GSM networks, it is to be expected that the type of transport chosen will be another that takes advantage of the greater capacity of the new network. Networks of other standards (cdma 2000, FOMA, etc.) make use of other transport protocols, although all require an MMSC message center.
Content synchronization through the SMIL protocol
- Multimedia messages are conceived as a multimedia presentation with text, images, sounds and videos displayed in a certain order. For this purpose, they make use of the SMIL language, or Synchronized Multimedia Integration Language. SMIL is a standard proposed by the WWW Consortium (W3C Consortium), with great similarity to the formatting language of web pages (HTML), and which is responsible for organizing and synchronizing the times when different types of content should be reproduced in the user terminal screen.
- Thus, a multimedia message is presented on the terminal screen as a group of one or more slides with text, images, sounds and videos presented in a certain order.
Multimedia messages are very similar to e-mail in that they can contain various types of content, and include information on the subject of the message and the option to send to multiple recipients. However, an email message consists of a main text and an optional group of attachments, which can be downloaded independently as desired by the user; Instead, a multimedia message consists of a main SMIL “script” and a group of files of various associated types, which are transported as a single unit. It is therefore not possible to separate the different types of content in the message; in transport, the multimedia message travels in its entirety, and the user must receive it in its entirety. Nor is it possible, in principle, to separate the type of content that is presented in an MMS, rather, it must be displayed in the order foreseen by the writer of the message; However, the terminals usually incorporate the ability to separate the content and store what is of interest in its internal memory to reuse it, forward it or re-view it whenever the user wishes.
The MMSC or message center [multimedia]
- The MMSC or multimedia message center (Multimedia Message Service Center) is similar in function to an SMSC short message center, although it has greater capacity and more advanced functions.
- The MMSC, in a GSM mobile system, must communicate with the GPRS core network for the transport of messages, with the network subsystem (NSS – VLR – HLR) for charging and user permission management, with an SMSC for forwarding notices of incoming messages and with the Internet to be able to send e-mails. In addition, the possibility is contemplated for the MMSC to recognize the characteristics of the user’s terminal (type and size of the screen, display capacity of certain types of file and not others, etc.) and automatically adapt the content received to the terminal so that look correctly.
- In other types of networks, the transport method will be different, but the MMSC will retain the ability to adapt the content, if this ability is enabled.
This is a summary of its functions:
- Receive incoming multimedia messages through the GPRS core network;
- Store incoming messages until they can be transported to the user;
- Send the messages to the user over the GPRS network when the user downloads them (normally, automatically at the request of their terminal);
- Receive and redirect outgoing MMS to the destination MMSC;
- Decide if the content type of the incoming messages is valid for the user’s terminal and, if necessary, process it so that it can be displayed;
- Communicate with the HLR and VLR to verify if the user has permission to send messages and to be able to rarify them.
WAP / GPRS connections and profiles
- The transport of the MMS between the user and the MMSC is done through a WAP GPRS connection; For this purpose, the user terminals accept different definitions of the WAP service profile depending on what is of interest. Thus, normally the operators specify a free WAP profile to transport the MMS; charging is done by the MMSC and is not done in the core GPRS network.
- Let us bear in mind that, normally, GPRS traffic has a cost, since it is used to connect to the Internet or the mobile WAP network. On the other hand, the GPRS traffic generated by multimedia messages is normally not charged, either when sending or receiving them, since it is easier for users and operators to charge them in bulk as messages, by the MMSC. However, if the user is outside the coverage of his operator (roaming) and receives or sends an MMS, it is likely that he will have to pay an amount for data traffic, when connecting to a foreign network that he will want to receive an amount for the data traffic carried out.
For this reason, it is advisable to deactivate the automatic reception of multimedia messages when going abroad or from our operator’s own coverage area to avoid high costs. These settings will be found in the phone menu, without the need to consult the operator to make them.