If your talking about ensuring that bandwidth is first used for SIP then any remaining bandwidth is used for other traffic then you need QoS.
QoS can be implemented in many ways. There are some questions that would need to be answered before I could be sure what you want.
A few primary questions:
- Do you know the IP address of the SIP server? If so you can just prioritize all traffic to or from that server.
- Do you know the IP address of the SIP device? If so you can prioritized any traffic to or from that device.
- Do you control the bottle necks in the path? If you are the ISP then you have much more ability to QoS the link.
- What is your interfaces maximum sustainable upload and download under a worse case scenario (meaning under heavy usage times)
Basically what your going to need to do is hold back traffic with a queue. I create interface queues that are slightly under the capacity of my link... for instance if the link can sustain 20Mbps I would create a 19.5Mpbs queue then inside of that queue (tree queueing) I would have multiple subqueues that do not have limits on them. The traffic is matched by in the subqueue and prioritized. This means that when the parent queue is full the voice traffic goes out before data traffic.
I prioritize all traffic to and from my SIP server to my clients on my network. Then secondarily any traffic with a set DSCP bit. Third in in priority is traffic that does not have a DSCP bit set. Finally I match any MikroTik bandwidth testing traffic and put it last. The bandwidth testing is last because I want to be able to test my network without interrupting my clients normal traffic.
If you are designing a large scale QoS implementation then know that this is not something to take lightly. Good QoS is extremely helpful. However just hacking QoS together may not do you any good and could even make situations worse. If this is just a home router then you don't need a grand plan and a lot of testing you just a few details regarding interface speed and some info that will identify the traffic and the interface queuing points.