How MMS works

Laymen explanation

MMS messages are delivered in a totally different way from SMS. The first step is for the sending device to encode the multimedia content in a fashion similar to sending a MIME e-mail (MIME content formats are defined in the MMS Message Encapsulation specification). The message is then forwarded to the carrier's MMS store and forward server, known as the MMSC (Multimedia Messaging Service Centre). If the receiver is on another carrier, then the MMSC [acts as a relay, and] forwards the message to the MMSC of the recipient's carrier using the Internet.[3]

Once the recipient's MMSC has received a message, it first determines whether the receiver's handset is "MMS capable", that it supports the standards for receiving MMS. If so, the content is extracted and sent to a temporary storage server with an HTTP front-end. An SMS "control message"(ping) containing the URL of the content is then sent to the recipient's handset to trigger the receiver's WAP browser to open and receive the content from the embedded URL. Several other messages are exchanged to indicate status of the delivery attempt.[4] Before delivering content, some MMSCs also include a conversion service that will attempt to modify the multimedia content into a format suitable for the receiver. This is known as "content adaptation".

If the receiver's handset is not MMS capable, the message is usually delivered to a web based service from where the content can be viewed from a normal internet browser. The URL for the content is usually sent to the receiver's phone in a normal text message. This behaviour is usually known as the "legacy experience" since content can still be received by a phone number, even if the phone itself does not support MMS.

The method for determining whether a handset is MMS capable is not specified by the standards. A database is usually maintained by the operator, and in it each mobile phone number is marked as being associated with a legacy handset or not. This method is unreliable, however, because customers can change their handset at will, and many of these databases are not updated dynamically.

Technical flow

MMS messages are delivered using a combination of SMS and WAP technologies.

When a mobile phone receives an MMS message, what it is actually receiving is an MMS notification message which it receives over SMS (WAP Push). This MMS notification message contains header information about the MMS message, and a URL pointer that the recipient must fetch in order to retrieve the content of the MMS message.

This URL pointer is a dynamically generated URL for the MMS message content which is stored on the MMSC. In a typical phone-to-phone MMS transaction, the process of sending and receiving the MMS message works like this:

• The sending phone initiates a data connection that provides TCP/IP network connectivity, usually over GPRS.

• The sending phone performs an HTTP POST to an MMSC of the MMS message encoding in the MMS Encapsulation Format, as defined by the Open Mobile Alliance. The encoded MMS message includes all of the content of the MMS message, as well as header information, including a list of intended recipients for the message. (Note: In most environments, the HTTP POST will be routed through a proxy server. Some devices will use wireless profiled HTTP and TCP through a WAP 2.0 proxy server, while other devices will use the Wireless Session Protocol, WSP, through a conventional WAP proxy server/gateway.)

• The MMSC receives the MMS message submission and validates the message sender.

• The MMSC stores the content of the MMS message and makes it available as a dynamically generated URL link.

• The MMSC generates an MMS notification message, which is sent via WAP Push over SMS to the message recipient(s). This MMS notification message contains a URL pointer to the dynamically generated MMS content.

• The recipient receives the MMS notification message. It then initiates a data connection that provides TCP/IP network connectivity (usually over GPRS).

• The recipient phone performs an HTTP (or WSP) get to retrieve the MMS message content URL from the MMSC.

Reference

https://en.wikipedia.org/wiki/Multimedia_Messaging_Service

http://www.nowsms.com/faq/how-mms-works