Quality of Service (QoS) is the secret sauce of many custom VOIP solutions. The big bottleneck for VOIP QoS and the place that causes most of the quality problems is the very first outbound link. This is frequently the slowest link, being a DSL or cable modem link of a little as 128k upstream. If you can get out that first link with delay and jitter under control, getting quality VOIP performance through the big pipes in the network will be no problem. The power of a DrayTek is its ability to identify precisely the traffic that is important and make sure it goes out that link first. In this example we have chosen the Vigor 2820 Dual WAN router. This router has one WAN with an ADSL modem and the other WAN has a 10/100 Megabit Ethernet. We identify our Asterisk PBX as the source of the traffic that needs to be prioritized, but this could be your Vonage ATA, a Grandstream ipPhone or anything else that produces VOIP packets.

Click on the graphic for a close up view.	VOIP Traffic Class For this example, we have used the WAN load balance capability to assign traffic from our PBX (192.168.100.20) to the ADSL link. Next, we create a traffic class and name it “VOIP Device”. The traffic class is a filter that looks for UDP traffic from our PBX in ports 10,000 and higher.
Click on the graphic for a close up view.	VOIP Bandwidth Allocation Since WAN1 (the ADSL link) will carry the VOIP traffic, we decided to assign 90% of the outbound bandwidth to VOIP. Now, we don't expect to use 90% of the 768k up-link for VOIP, but if that bandwidth isn't being used by VOIP, it will be borrowed by other traffic. WAN2 is now a fail over port for the VOIP traffic, on this link we have only assigned 25% to VOIP.
Click on the graphic for a close up view.	Results for One Voice Call So now we can look at what happens when we have one voice call on this ADSL line. You see there is 4000 Bytes (32 kbits) per second of VOIP traffic on the link and not much else going on.
Click on the graphic for a close up view.	Bandwidth Borrowing Now lets run a speed test on the DSL Link and see what happens. The speed test bandwidth uses the "Other" category. Speed Test uses 60,000 Bytes per second (540 kbits), which absorbs almost all of the available bandwidth, but leaves the VOIP intact. Clearly the speed test “borrowed” some of that 90% assigned to VOIP.
Click on the graphic for a close up view.	Prioritized Traffic creates VOIP Quality of Service Now lets add some more voice conversations to the link and run the speed test again. Now our speed test shows the upstream speed is only 356 Kbits per second. The other 200 Kbits is being consumed by the VOIP Traffic. Clearly the router managed the bandwidth to maintain the quality of the VOIP channels. But the most important result: crystal clear VOIP quality too.

VOIP QoS Planning

As you plan your VOIP installation, keep in mind that the most important factor for the quality of service of the VOIP calls is the priority assigned on the first outbound link. Picking a product that can quickly and accurately identify and prioritize the important voice traffic is the critical issue for your quality of service.

You must also consider other factors to guarantee the best voice quality. Segregating VOIP and data into separate broadcast groups (Virtual LAN / VLAN) can be important in some networks. The use of Virtual Private Networks (VPN) to remote locations are critical to maintain services to remote IP phones; don't forget to think about how you will apply QoS to that remote IP phone over the VPN.

DrayTek products are amazingly economical given their power. If you have a simple SoHo installation, the built-in ATA in all "V" models automatically prioritizes the VOIP from the ATA. If you have a more complex environment, the product line can scale to as much sophistication as you need. DrayTek can deliver quality VOIP over VPN solutions for as little as $130. Most products support untagged VLANs and the 3300v supports tagged VLAN. Combine this router with your favorite flavor of Asterisk and you have a very low cost product that will provide a very impressive result for you and your customers. Some DrayTek products are available in plain label configurations too (as low as quantity 1) and can make a great anchor for your branding campaign.

To buy a DrayTek router with VOIP QoS online try Guideband.