Hi, > > may I ask a simply question? Is it possible to send DCCP packets at > other times than those calculated by the rate control? I mean, is it > possible to call a send socket call with an option saying, send this > packet immediately no matter that the rate control is saying to you? > In my opinion and experience, this is possible - after all, DCCP calculates the *suggested* sending rate. For example, the calculated inter-packet interval is 0.1 ms over a general purpose PC (installed a modern Linux kernel). Also, assume the host OS clock granularity is 4 ms (i.e., 250 Hz) - well, some Linux kernels have configured at higher rate than this but not more than 1000 Hz. Then, there would be the cases that the OS clock did not schedule the real-time application in time such that the application cannot actually maintain the calculated inter-packet interval correctly. When the application is scheduled next time, the application would need to send the packets which have not been able to transmitted due to the OS clock granularity. Caveat: What we need to be careful is that the application should not send much faster than the DCCP rate, because it may introduce (unwanted) persistent packet losses. As we know, the packet losses can degrade the performance of the multimedia applications significantly. > The role of DCCP would be to calculate the proposed sending rate and > to measure the network round trip time. This data is then used by an > application specific rate control. Correct. > > The background of my questions is based on the experience, that > real-time packets shall be send immediately, especially if a scenario > of very interactivity is given, and that some codecs cannot change > their sending rate immediately but need some extra time (e.g. one or > two additional frame periods). Thus, a less strict sending schedule > would help. > You might want to change the codec itself to interact with DCCP in real time, so that the codec can change the necessary parameters (e.g., various encoding parameters) when needed. Cheers, Soo-Hyun
