Over provisioning bandwidthSince lack of bandwidth leads to many of the QoS problems we have discussed, it makes sense to increase bandwidth. It is also difficult to analyze the requirements of VoIP and integrate it with the other data needs of the network. Buying more bandwidth than you need is a sensible reaction to this situation. On the company LAN this is realistic and cost effective since the cost of Ethernet components is at an all time low. If the LAN uses 10 Mbps Ethernet, upgrade to 100 Mbps. If the LAN is already 100 Mbps, upgrade the backbone or switch/router links to Gigabit Ethernet.
Buying more WAN bandwidth can be a serious proposition for a company because there will be increased monthly expenses that will affect the bottom line. In this situation, a serious analysis of the company needs should be undertaken in an effort to minimize WAN costs.
Dealing with delayDelay is a complex topic since it can be introduced at so many places along the path that the voice travels end-to-end.
Algorithmic (codec) delay
Voice has to be captured and the codec has to digitize, quantize, compress and silence suppress it before passing it onto the protocol stack. Codecs introduce different delays depending on their processing needs. In general, the more processing required because of compression, the more time delay is introduced. A trade off between compression efficiency and time delay needs to be made and possibly, the system may need to switch over to a different codec.
Since the voice packet has to be processed by so many machines, including the end-point telephones and user PCs, call managers, gatekeepers, gateways and routers, the power of these machines affects the delays introduced during transmission. Machines may need to be upgraded to produce acceptable voice quality.
Network induced delay
On a congested network, the voice packets are mingled with data packets and are treated the same. This can mean they are delayed or discarded. The easy way to deal with the problem is to over provision the LAN with more bandwidth than needed. Since this may not be feasible or cost effective with a WAN, other techniques are needed. The next section delves into some of the techniques used to give voice a higher priority than data on the network.
Handling jitterSince jitter is the variance in the delay of packets arriving, it can be compensated for by using a playout buffer. The playout buffer receives the packets in the uneven intervals that they arrive and then plays them out to the receiver at a steady pace.
Suppressing echoAll VoIP circuits use echo cancellers. The echo canceller compares the voice data received from the packet network with voice data being transmitted to the packet network. The echo from the telephone network hybrid is removed by a digital filter on the transmit path into the packet network.