QoS (Quality of Service)
From Bandipedia
When considering a VoIP solution provider it is important to understand the Quality of Service (QoS) mechanisms your VoIP provider utilizes to ensure the highest levels of call quality. The main factor affecting VoIP call quality is congestion across a network. When networks get bogged down with Internet data (i.e. downloads, uploads, streaming content, etc.), voice data can be lost (packet loss) or held up by incoming data traffic leading to jitter.
QoS is a defined level of performance in a data communications system. For example, to ensure that VoIP service is delivered with minimal packet loss or jitter, service providers offer solutions at primary congestion points to guarantee a specific level of quality. These congestion points are at the customer’s edge router/CPE or on the customer’s port with their IP service provider. Maximum QoS benefit is realized from CoS at the provider edge and a QoS devise on the customer LAN.
To prevent congestion on the customer’s network edge, Bandwidth.com can provide a QoS router on the customer’s premise. For outbound calls, packet prioritization is used during times of congestion whereby voice packets in the router’s queue are prioritized over data packets when network congestion reaches a determined threshold (typically 70%). Once the device detects that the congestion threshold has been violated, non-VoIP (i.e. data) packets running across the Local Area Network (LAN) are throttled back, giving priority to voice packets along the remaining bandwidth – greatly reducing or eliminating packet loss and jitter.
Inbound calls are handled through traffic shaping. That is, during times of congestion inbound voice traffic may find itself trapped behind incoming data packets. If the router receives a request to accept an inbound call, it will automatically check to ensure bandwidth is available. If it finds data flows are consuming too much bandwidth, it will instantaneously signal data hosts to throttle back its traffic flow. Once this occurs and the necessary bandwidth has been freed up, it will accept the VoIP call which will travel unimpeded through the customer’s network.
Generally, when enough bandwidth is available, QoS is not an issue and the QoS devise is idle until congestion is detected.
The second possible congestion point for voice packet delivery is at the customer’s port with their IP service provider. Service providers offer Class of Service at their edge router in which packets are treated with different class levels. For instance, a VoIP packet may be in the Expedite Forward (EF) class while a web data packet may be in the Best Effort (BE) class thereby giving priority to voice traffic and reducing packet loss and jitter.
Packet Loss – Voice data is sent in “packets†of information. Packet loss is the measurement of packets successfully transmitted to the total number originally sent. A clean and properly maintained LAN and QoS router on the customer premise paired with a CoS (Class of Service) solution at the providers edge can greatly reduce packet loss.
Jitter – In a perfect world, voice packets travel across a network at the same rate of speed, evenly spaced so they are heard at their destination without distortion. Due to congestion, primarily at edge routers, the timing between voice packets may be shorter, longer, or shifted out of order, causing call distortion. A clean and properly maintained LAN and QoS router on the customer premise paired with a CoS solution at the providers edge can greatly reduce jitter.
Latency – The amount of time it takes data to travel from point A to point B is latency — the greater the distance, the greater the latency. Luckily, we live in a small world where voice packet latency is not really an issue and often the lag is indiscernible.
- Buy more bandwidth or use a dedicated circuit for voice
- Install QoS device at the edge of your LAN
- Invest in CoS at the provider network edge
- Make sure that your T1 is a completely secure circuit dedicated for your purposes, i.e., not a circuit you share with other users. (Many 2nd and 3rd tier providers oversubscribe the port in such a way that at times of peak traffic you won't get your full T1 connectivity)
- Choose a business-class over residential-class VoIP provider. (Business-class providers send voice data exclusively over Tier 1 carrier networks. Residential providers may use Tier 2 and Tier 3 networks, resulting in poor call quality users cannot control even with QoS solutions)
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