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About QoS for VoIP

Setting QoS for VoIP connections.


Setting QoS on your router can help prevent choppy voice and improve the quality of your VoIP connection.  Giving priority to voice and VoIP traffic though your router will prevent other applications from having the same high priority level of service and should help maintain better data flow and a better voice connection. 

First basic simple QoS information.

QoS (Quality of Service) is essentially a service that prioritizes certain data traffic by slowing less important data packets down.  These important packets then reach their destination as quickly as possible.   The service with the higher priority gets to pass through the router first, lowering the delay that it might experience without QoS set.  It cannot make that application or data pass through faster than it would without any competing data traffic present, but when there is other data present can be given the priority to move up to the front of the queue and pass.  Queues are holding containers of data for a network device(s) when that data cannot be sent immediately.  Typically, routers use a FIFO (First In, First Out) method unless Setting up QoS for VoIP can help correct choppy audio. some other configuration has been enabled, such as QoS tagging. 

When a router is able to project how much data it can receive, it then shapes the traffic by queuing packets, delaying low priority packets while letting high priority packets proceed.  The QoS tags can have varying levels of importance, from high to medium to low or critical, important or best-effort, depending on the router and can be prioritized by a number of different methods.  The most notable types of tagging is small routers are the actual Ethernet port of the router, the MAC address of the endpoint, and the TCP or UDP port.

What QoS settings can do for VoIP connections.

First, to understand what QoS settings can accomplish for VoIP, we need to clarify that the router where the QoS will be implemented should be located in the LAN as a gateway device.  The location would typically be after the DSL or cable modem and not after the VoIP ATA.  Proper QoS can:

  • Reduce or eliminate conversations from experiencing choppy voice due to other applications grabbing the needed bandwidth available forcing the voice stream to queue up.  Typical applications might include email, gaming and high bandwidth applications.

What QoS settings cannot do for VoIP.

Setting QoS on the router on your network will not have an impact on your ISP's performance.  Typically, your ISP is already setting limits on your download and upload, which will be related as your ISP's Level of Service.  Knowing what you should be getting in terms of your available bandwidth, both on the upload and download, should be something that you know, if not, do some speed test measurements and then check that with what your ISP tells you is your Level of Service.  If you are not receiving at least 80% of what is the cap, then spend time with your ISP's tech support troubleshooting this issue before moving on to other changes.

What you should do before setting QoS for VoIP.

We suggest that you try the following steps if you are experiencing choppy voice, before setting any QoS settings on your router.  These first steps might alleviate the issues and provide for a cleaner start to any other configurations that you might set.

  • Try talking on your VoIP phone without any competing computers or other IP phones and see if the problem exists.  If it does try a G729 Codec setting (some providers call it a "bandwidth saving" setting.
  • Make sure that any computers on the LAN are clean of spyware.  Check them by using your protection software, including an online Onecare scan.
  • See our help and tutorials on VoIP troubleshooting.

Setting up QoS for most Linksys routers should be an exercise in frugality, picking the simplest settings to achieve the desired results.  As the new setting(s) work, then the addition of more advanced settings can be added to prioritize other applications.  If the results are not what you would expect, simplify to the most basic QoS and see if that works.  Remember that VoIP service providers vary and some providers use sophisticated Session Border Controllers that negotiate VoIP calls from each endpoint and can have effects on the call which may override the QoS markings that your router places on the packets.  Continue with our information about setting QoS for VoIP or setting up QoS on Linksys routers and read about the 3 main types of QoS.