Does VoIP require QoS even though the WAN link has so much bandwidth to be able to handle data/voice

Does VoIP require QoS even though the WAN link has so much bandwidth to be able to handle data/voice

Does VoIP require QoS even though the WAN link has so much bandwidth to be able to handle data/voice traffic?

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Consider a WAN serial link that can support 1.5 Mbps. Lets say that your phone system or router is only going to allow 30 G.729 calls simultaneously over the WAN. The approximate bandwidth then required for a voice call is about 27 kb/s. The total bandwidth required for the maximum number of voice calls is about 810 kb/s. This leaves 690 kb/s for data traffic. Now consider that multiple people inside the company want to download large files using FTP. Once these files start to download, the voice quality may degrade unless there is something throttling the bandwidth (I.E. Packeteer type solution) or QoS is enabled on the routers on both ends of the serial link.

If the maximum bandwidth consumed by data downloads plus the maximum bandwidth consumed for voice is less than or equal to the overall available bandwidth on the WAN, there would be no concern. A WAN link with that kind of bandwidth would be rather expensive and out of reach for almost any business.

This was first published in May 2004