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Original Publication Date: 2001-Apr-27
Included in the Prior Art Database: 2001-Apr-27
Document File: 3 page(s) / 23K

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Jheroen Dorenbosch: AUTHOR



This text was extracted from a RTF document.
This is the abbreviated version, containing approximately 46% of the total text.


by Jheroen Dorenbosch

In dual-mode a GPRS Mobile Station (MS) can do legacy, circuit switched voice and packet data at the same time. The switch (MSC) manages the voice connection. It is circuit switched on a full, a half or a quarter rate traffic channel (TCH or TCH/H). Voice uses a standard GSM vocoder. The GGSN and SGSN manage the packet data connection over a packet data traffic channel (PDTCH or PDTCH/H).

A particularly efficient dual-mode uses two half rate channels, a TCH/H and a PDTCH/H that use the same slot in alternating frames. Currently the GSM/GPRS standards are being changed to allow for better coordination between the MSC and the SGSN. This will allow for simultaneous hand over of the voice and packet data channels.

In dual-mode one can browse while talking to someone on the phone. Implementation is eased because voice and data have no functional or temporal relationship. However, one can not use dual-mode for a multi-media video conference, for a streaming voice/video or for animated advertisements. The problem is that there is no synchronization between the voice and data channels.

The PDN uses the Real Time Protocol (rfc 1889) timestamps for synchronization which are lost on the voice channel.

Another problem is that the voice and image data may follow very different routes. Voice data may come from the PSTN via MSC, while image data comes from the PDN via the GGSN and SGSN. They come together at the BSC. What is needed is a new architecture that allows voice and image data to both come through the PDN as packet data and to be transmitted in dual-mode. This would provide an interim solution while waiting for true wireless Voice Over IP.

The solution involves the use an explicit synchronization message between the infrastructure and the MS to synchronize the presentation of voice and image data in dual-mode. The message provides the information needed to combine and synchronize the voice stream carried by a conventional wireless voice channel normally associated with a circuit switched connection, and the image packet data stream carried by a conventional wireless packet data channel. The newly defined message is preferably sent on the packet data channel, at the signaling or application layer.

For PDN initiated multi-media, the message is sent by the system to the MS. It indicates:

that the voice channel received in dual-mode is related to a (specified) received packet data stream.

that the packet data stream will contain the time stamps (as in RTP).

the amount of time that the voice stream is delayed with respect to real time (delay value).

The MS will then buffer the voice and image streams and delay their presentation to provide perfect synchronization.

For MS initiated multi-media, an MS that wants to initiate multi-media in dual-mode sends a messa...