Re: [codec] #17: Feedback and control loop?
"codec issue tracker" <trac@tools.ietf.org> Sun, 02 May 2010 18:08 UTC
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Subject: Re: [codec] #17: Feedback and control loop?
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#17: Feedback and control loop? ------------------------------------+--------------------------------------- Reporter: hoene@… | Owner: Type: enhancement | Status: new Priority: minor | Milestone: Component: requirements | Version: Severity: Active WG Document | Keywords: ------------------------------------+--------------------------------------- Comment(by hoene@…): [Christian]: Requirement: Reliable on the Internet The ACS must be optimized towards acoustic real-time communications over the Internet, and must have the flexibility to adjust to the environment it operates in. Based on the quality of the end-to-end speech packet transmission, the codec should adapt its quality and delay to achieve an optimal benefit for the user. As most Internet transport, it should be used with a wide range of condition allowing a high reliability regardless the networking condition. The reliability of the audio transmission should be high, even in cases of low and varying bandwidth. This implies that the codec is used on top of a transport protocol that implements a congestion control algorithm and that the ACS adapts to changes of available bandwidth. For example, if the available transmission bandwidth is too low to allow the codec to transmit audio at a high quality, the application can lower the sampling, bit or frame rate of the stream at the cost of higher algorithmic delay or a degraded audio quality. Reiability and congestion control : The acoustic transmission should be reliable and robust. The ACS shall be not only robust against packet losses but also for periods of low bandwidth. The mean availability of the audio transmissions, calculated over all users, might be one of the metrics for assessing the performance of an Internet audio codec. The ACS should adapt to the current network situation. Also, the codecs of ACS themselves must be adaptable, because switching among multiple codecs is difficult to negotiate and unlikely to work well in situations of inter-operation. Responding to congestion is a more complex issue and out of the scope of this document. However, it shall be defined on how to use existing congestion control protocols like DCCP and TCP. The ACS shall provide the mechanisms that congestion control requires from the codec (i.e. bitrate/framerate adaptability). Because of the interactive nature of the acoustic transmission, the bidirectional transmission of audio content can be used for transmitting the required feedback and implementing a control loop. Side channel Congestion control should be must for all Internet applications also for the ACS. [RFC3550] suggests in Chapter 10 somewhere that the RTP profile should care for rate adaptation. Thus, the ACS should take advantage of a feedback loop for variable coding parameter control in order to allow a wide range of operation and to adapt to the the current available bandwidth and processing power. Congestion control per se is outside the review of this group, but providing the hooks for a congestion-control mechanism to interact with the codec is quite important. For example, running this codec on a TFRC-enabled or DCCP RTP stream - TFRC and DCCP need to be able to adjust (via the application) the bitrate of the codec in order to implement congestion control and perhaps adjust packetization periods/packet-rates. A side channel for adaptation can be added. This would make sense because in usage scenarios audio is always transmitted in both directions. Adding a control channel would give a real advantage to existing codec designs. Alternatively, such as side channel can be also added with alternative solutions, such as handling that communication in SIP/SDP and in RTP/RTCP. -- Ticket URL: <http://trac.tools.ietf.org/wg/codec/trac/ticket/17#comment:2> codec <http://tools.ietf.org/codec/>
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- Re: [codec] #17: Feedback and control loop? Christian Hoene
- Re: [codec] #17: Feedback and control loop? codec issue tracker