Mobile Blog: Video, Media, Augmented Reality, Rich Media, IVVR

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In desktop video conferencing, the video conferencing application is normally bundled to an Instant Messaging software that includes text chat capabilities. Users can appoint or prearrange a video conference using textual chat. In contrast, the current evolution of video telephony in UMTS (Universal Mobile Telecommunications System) networks based on the circuit-switched 3G-324M service does not seamlessly combine video conferencing with other communication channels. The notion of video telephony in the mobile environment is nearer to standard voice calling than in the stationary world. Therefore, it is more likely that somebody will place a video call without prior announcement. This leads to privacy and inconvenience concerns. The callee might not want to be seen during a conversation for a variety reasons: A video call

photo credit: Iain Farrell

Even with a great deal of marketing, early attempts to convert users to the video telephony technology flopped (Jones and Marsden). In contrast, desktop video conferencing is incredibly popular for private person-to-person conversations and widely used for video conferencing in business environments such as telepresence for computer-supported cooperative work (CSCW).

In desktop video conferencing scenarios, typically a stationary computer is used. Camera and microphone are fixed and usually maintain the same distance from the person participating during the conversation. Moreover, lighting conditions are generally better than

photo credit: Steven Fernandez

Media compression, error concealment measures, and the characteristics of wireless networks have side effects on the quality of 3G video telephony and IVVR (Interactive Voice & Video Response) applications.

3G-324M requires only the use of speech codecs. In contrast to audio codecs, speech codecs are designed for speech transmission within a narrow frequency range, making them inappropriate for transmission of music or a range of artificial sounds. This fact needs to be considered when designing IVVR applications

photo credit: Etwood

To assess the interactivity of IVVR (Interactive Voice & Video Response) applications, it should be explained how different delays in an IVVR system add together and create the overall interaction delay d:

d=d_t+d_nr+d_c+d_g+d_nt+d_r

where d_t is the transmission delay of the 3G network from the MS (Mobile Station) to the PLMN (Public Land Mobile Network) border. The delay caused by transition from one network to another is represented by d_nr; this is mainly the transition from a CS (Circuit-Switched) network (part of the 3G network) to a PS (Packet-Switched) network (IP). This transition is obvious in the following scenario:

The dialled number is routed over the PSTN (Public Switched Telephone Network) to a PRI (Primary Rate Interface) in a datacentre and answered by a 3G-324M Gateway directly connected by a digital telephony card to the PRI line. In this case, it is assumed that the path between the MS to the answering gateway is completely circuit-switched. When the gateway routes the video call over an IP-based LAN (Local Area Network) to an IVVR Application Server there is a transition from the CS to the PS domain. This transition causes delays because the continuous bitstream needs to be wrapped in packets to transmit the data over a LAN.

On the other hand, d_nr can also describe delays caused by network transitions between the PLMN border and an E1 line. Nowadays, to reduce costs, parts of the PSTN are already replaced by NGN (Next Generation Network) that use the PS domain to interconnect circuit-switched networks for voice and video communication.

d_c describes the delay caused on an application server to control the flow of program execution depending on user input.

d_g is the delay caused by dynamic generation of an audio and video stream to be transmitted and displayed on the MS.

Similar to d_nr, the variable d_nt describes delays caused when sending media from an IVVR Application Server to the MS. The transition from the PS domain (LAN) to the CS domain (E1 line) particularly causes delays due to packet delay variation. Packet delay variation

Auch wenn seit dem 13. November 2008 schon einige Monate vergangen sind, m