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The QoS feature is disabled in the DVG firmware and TBB PSTN Gateways since there is no standardized QoS capability amongst ISPs at this time. The TOS1 and other bytes currently used to control QoS are ignored by most ISPs, thus providing no QoS capability.
•Even with DVG QoS disabled, most TBB users will get great PSTN like call quality - notwithstanding network issues as described in Internet Connection and ISP which can lead to "choppy" audio. Any given TBB user will encounter a congestion free VoIP call, most of the time.
•However, call quality will suffer if you consistently maximize use of your Broadband bandwidth, or stress the DVG ATA.
For most VoIP users, the lack of QoS at the current time simply implies that when there is severe Internet congestion in the path that a VoIP call takes, there may be some degradation on the call - sound cutting out, or lag/delay. This may occur for only one second or it may be a larger amount of time (10secs+); as determined by the congestion itself. This is impossible to determine in advance as the Internet is inherently a distributed system, and congestion can occur at various times and places - much like traffic on a highway. Unlike rush hour highway traffic, your VoIP calls will NOT be a problem every evening - it all depends on what is going on in the path your VoIP call is taking. This will change with every call you make!
As quoted from a Primus post in the Forum:
This was in response to user (Number6) providing the following details about the TOS byte in TBB VoIP packets from the ATA:
In order for us to get full benefit from QoS, all the ISPs involved in passing the packet from you to us (or vice versa) would need to respect our TOS, Diffserv, or other settings. Most ISPs erase such things on the way in and out of their networks, which has been our experience in the Canadian market, unfortunately.
1TOS - Type of Service
I have been working on ways to modify the QoS of my router to improve the quality and minimize the latency of VoIP packets being sent to/from my DVG gateway. During this tweaking I have noticed that although the TOS field of the packets originating from my DVG is set to 0xb8, the TOS field of packets being sent by Primus is set to 0.