When it comes to optimizing, the internet link for VoIP there is one way to ensure you have an easier life if you have the budget and that is by provisioning a dedicated VoIP internet link to your hosted IP/PBX provider. This can be arranged through your service provider and the local telecom company. The Telco can arrange fixed line T1/E1 links or better virtual lease lines over point-to-point MPLS private wires. If your budget doesn’t stretch to that or the services are just not available in your area then buying another ADSL link to the internet is a good cheap alternative, which you can use solely for VoIP. This way you will have all the bandwidth available for calls without any contention issues. If you are using a Unified Communications solution whereby you have video conferencing and other such video services then you really should have a dedicated link anyway. However, should your budget not stretch to adding a dedicated internet link what are the other options available?
If you cannot provision a dedicated internet link for the VoIP and Video services, which would free them from bandwidth contention and traffic congestion over your internet link, then the alternative is to create a virtual link. What you will need to do is to implement Quality of Service (QoS) and if you can Traffic Policing and Shaping.
QoS is available on just about all modern routers likely to be found in Small Office Home Office (SoHo) environments. It can easily be configured via the browser based configuration portal on the router. It is normally accessed via an address such as 192.168.1.1 or 192.168.1.254 or something similar – check the back of the router or on the manufacturer’s website for details.
The QoS feature will be normally switched off, so you need only enable it by ticking a checkbox. The next thing you have to do is then select the priority that you wish to assign different classes of traffic. All IP traffic by default will be at best effort or low priority. What you have to do is select VoIP and assign it to the highest priority available. It doesn’t really matter what, these routers classes vary along the lines of low-medium-high, so long as it is assigned a priority higher than any other traffic on the router.
Now that you have assigned VoIP the highest priority you can, try it out and guess what … most likely nothing has changed there is no discernible change in quality. Don’t worry that is perfectly normal. You see what happens is QoS is actually a priority queuing system it controls the depth and order that packets queue when at the interface output queue awaiting to be fed out onto the wire. So, if there is no congestion at the queue then QoS has no effect whatsoever. QoS only kicks in if there is congestion.
This is why really it is better to address quality issues by provisioning bandwidth. If you have sufficient bandwidth you have no need for QoS as it will be rarely if ever required. However, on the small SoHo router it is easy to configure so you should enable it anyway as it probably will be required if your bandwidth is on the low side.
With regards larger businesses with medium sized routers perhaps by Cisco then there are far more optimization tricks you can play with. QoS is implemented in Cisco either via the web based GUI or by the IOS command line. Here we want to do the same as on the SoHo router and prioritize VoIP traffic by giving it a priority of 5 (Priority queue) and video as 4 (next highest). However, as the Cisco router is far more configurable than the small SoHo routers we can also look at configuring Traffic policing and shaping by configuring policy maps and assigning bandwidth per class of traffic.
Traffic policing and shaping uses policy maps, which are used to match traffic by certain criteria, such as the interface it arrived on, by protocol, its ports numbers or priority. We can identify and mark traffic and assign them to a certain class. We can then set permitted bandwidth limits for each class. What this does is virtual creates separate tunnels for each class. By assigning VoIP for example 30% of the available bandwidth and WWW traffic 20% and leave the remaining 50% for all the other protocols and applications we can ensure that even under the most congested traffic situations that we will have that bandwidth reserved for VoIP.
QoS and Traffic Policing and shaping are useful tools if your network is regularly facing congestion. However, bandwidth is rarely today expensive to upgrade and it should be your first choice. Only if bandwidth for whatever reason cannot be upgraded to remove the congestions should you consider QoS as a solution – it is not it is a short-term firefighting technique.