Yakir, > I am attempting a brave move from 1.7 to 2.1 on ARM. > One thing that has popped up straight away was the absence of the > rohc_feedback. The following snippet is from 1.7, > > [snip code] > > Post 1.7, has the feedback handling been made implicit?
You're right, feedback handling changed between 1.6.x and 1.7.x. The 1.7.x versions also handled the old API, but versions 2.0.0 (or any later version) dropped it. The new way to handle feedback is now more flexible: handling both piggy-backing or feedback-only channels becomes possible. The API changes are described on the wiki: https://rohc-lib.org/wiki/doku.php?id=library-migration#api_changes_between_16x_and_17x However, the feedback changes are not described. Here are some explanations. If you find them helpful, I'll add them to the wiki. The feedbacks are transmitted in two ways: * piggybacked with one ROHC packet that goes in the other direction * sent alone. Piggybacking may saves bandwidth, however it requires some return traffic. If there is no return traffic, the feedbacks shall be sent alone in order to avoid adding jitter. The behaviour might be controlled by an application with a timeout: queue the feedbacks until a return packet arrives or the times out. When feedback are piggybacked, the decompressor is associated to a local compressor that will transmit the feedback over the network. The remote decompressor will extract the feedback and give it to the local compressor that will interpret it. comp. A ----[ROHC for A + feedback for B]---> decomp. A /\ | | | feedback for comp. A | feedback for comp. B | + | + | feedback for comp. B | feedback for comp. A | | \/ decomp. B <---[ROHC for B + feedback for A]---- comp. B The rohc_decompress3() function allows you to perform both transmission ways. The function returns two feedbacks: * The 4th parameter is the feedback sent by the remote decompressor that shall be delivered to the local compressor. The function rohc_comp_deliver_feedback2() may be used for the delivery. * The 5th parameter is the feedback that the local decompressor wants to transmit to its remote compressor. That packet may be sent as-is over the network, or it may be prepended to any ROHC packet generated by the local compressor. The test/non_regression/test_non_regression.c uses two couples of ROHC compressor/decompressor that use each other for piggybacking. A more complete application than the non-regression test should handle the case in which there is no traffic in the other direction. To achieve that, the application may store all generated feedbacks locally. Then: 1/ If a packet goes the reverse way, then you build a ROHC packet with: a/ the stored feedbacks b/ the ROHC packet generated by the rohc_compress4() function. You may concatenate them together: 1 or more feedbacks first then the ROHC packet itself. The only limit is the MTU of your link layer. 2/ If no packet goes the reverse way for a long time, then you send all the stored feedbacks to your link layer. The decompressor will handle them fine: the rohc_decompress3() function returns ROHC_STATUS_OK and an empty decompressed packet (3rd argument of the function). You are not the only one struggling with feedback handling. I should maybe add a "simple" API that makes easy to create a couple of local compressor and decompressor. It could hide the details and handle feedback between the local (de)compressors transparently for the library users. Something that could look like: /* create couple */ rohc_couple = rohc_couple_new(ROHC_SMALL_CID, ROHC_SMALL_CID_MAX, random_cb, NULL); if(rohc_couple == NULL) { /* handle error */ } /* decompress one ROHC packet: - internally deliver the feedback sent by the remote decompressor to the local compressor, - decompress any compressed packet into the provided 'uncompressed_packet' buffer (some ROHC packets may contains only feedback, resulting in no uncompressed packet), - internally store the feedback that the local decompressor wants to transmit to its remote compressor. */ status = rohc_couple_decompress(rohc_couple, rohc_packet, &uncompressed_packet); if(status != ROHC_STATUS_OK) { /* handle error */ } if(uncompressed_packet.len != 0) { /* uncompressed packet is available, do something with it */ } /* sometimes later, compress one uncompressed packet */ status = rohc_couple_compress(rohc_couple, uncompressed_packet, &rohc_packet); if(status != ROHC_STATUS_OK) { /* handle error */ } /* compressed packet is available with piggybacked feedback, send it to the remote node */ /* if there is no packet to compress, one may flush the stored feedback */ status = rohc_couple_flush(rohc_couple, &rohc_packet); if(status != ROHC_STATUS_OK) { /* handle error */ } /* compressed packet is available with feedback information only, send it to the remote node */ What do you think of? > PS. BTW, thanks for other 32bit CPU kernel div64 fix --- will test > this soon OK. Keep me informed please. Regards, Didier _______________________________________________ Mailing list: https://launchpad.net/~rohc Post to : rohc@lists.launchpad.net Unsubscribe : https://launchpad.net/~rohc More help : https://help.launchpad.net/ListHelp
