I've got a small ISP feed (15 / 1 Mbps) and a VoIP device that can handle fax services. The VoIP device is behind my Western Digital My Net N600 running CC 15.05 with SQM, and is currently an equal peer with all my other network traffic. Voice quality is acceptable.
I find that if all other traffic is disconnected I can routinely send faxes over VoIP through my OpenWRT router. But even with SQM / fq-codel / simple.qos I get fax communication errors when other traffic is competing for bandwidth.
I am hoping to give outgoing packets from the VoIP device absolute priority, but I don't understand the tc command well enough yet.
My question is: should I spend my time studying the tc command, and try to tailor a fq_codel .qos script to give priority, or is my time better spent getting the cake qdisc installed (it isn't part of my 15.05 version) and then trying to configure a cake .qos script?
Out of curiosity -- why are the layer_cake and piece_of_cake .qos scripts included if the cake qdisc is not?