On Mon, Mar 9, 2015 at 5:03 PM, Yousf Ateya <[email protected]> wrote: > While browsing some pcap captures of IAX channel, I found many LAGRQ and > LAGRP packets (once per 10 seconds for each call). > > So, I traced LAGRQ and LAGRP use in code and found that it is almost > useless; it sets iaxs[fr->callno]->lag which is not used anywhere else. > > Almost same functionality (calculate lag) can be achieved using PING/PONG. > > Is it left for RFC-compatability only? Or there something I didn't notice? >
Quoting from the IAX2 RFC: 6.7.4 LAGRQ Lag Request Message A LAGRQ is a lag request. It is sent to determine the lag between two IAX endpoints, including the amount of time used to process a frame through a jitter buffer (if any). It requires a clock-based time-stamp, and MUST be answered with a LAGRP, which MUST echo the LAGRQ's time-stamp. The lag between the two peers can be computed on the peer sending the LAGRQ by comparing the time-stamp of the LAGRQ and the time the LAGRP was received. This message does not require any IEs. Note that this is similar to PING/POKEs, except that it is used explicitly to measure the time between request/response *including* the time it takes for a frame to traverse a jitter buffer. That isn't exactly the same as the PING/POKE functionality, which is more about reachability (and the time to reach the endpoint) then it is about media quality. That being said, you are correct that nothing currently uses that value. It is simply stored on the pvt and updated when a LAGRP is received for a transmitted LAGRQ. Theoretically, something could report on the quality of the call using the lag value (in a manner similar to RTCP call quality statistics), but it does not appear as if that was ever done. -- Matthew Jordan Digium, Inc. | Director of Technology 445 Jan Davis Drive NW - Huntsville, AL 35806 - USA Check us out at: http://digium.com & http://asterisk.org -- _____________________________________________________________________ -- Bandwidth and Colocation Provided by http://www.api-digital.com -- asterisk-dev mailing list To UNSUBSCRIBE or update options visit: http://lists.digium.com/mailman/listinfo/asterisk-dev
