What is QoS?

Quality of Service (QoS) is the ability to deliver specific applications ahead of others over a routed IP Network.  Examples of QoS include; Email, Customer Relationship Management Software (CRM), Voice (VoIP) and Video.  QoS is typically applied to VoIP and video traffic because they are time sensitive.

QoS works by having a router recognize voice packets and routing them ahead of non-time sensitive data packets.  Network administrators may be concerned with the degradation of their overall network performance when implementing QoS.  If properly engineered, end-users will see very little, if any, performance degradation of their non-voice applications.

QoS Misconceptions: It is very common for a Network Engineer (MCSE) to equate quantity with QoS.  In other words “the voice conversation is only taking up 32K of my 1,544K circuit therefore I do not need QoS”.  Although the size of the pipe can sometimes ‘mask’ the necessity for QoS in the short term, poor voice quality will ultimately prevail.

QoS and the Internet:  Although premise based internet routers can be programmed to recognize the QoS tags on each voice packet sent over the internet, your internet service provider’s (ISP) router strips the tags at their first opportunity, making the internet an unmanaged network.  Unmanaged networks typically do not produce acceptable voice quality.  The only exception to this rule is when your ISP sells you SIP Trunks for utilization with your IP/PBX.  The ISP can then manage the connection between their central office and your premise based equipment because they ‘own’ the circuit.

QoS and Virtual Private Network (VPN): A virtual private network encrypts the data sent between two or more points over the internet.  The same rules that apply to QoS and the internet also apply to QoS and VPN.

SIP Trunk Providers: Many SIP Trunk providers advertise very attractive prices when connecting to their Central Office over the internet.  The same rules that apply to QoS and the internet also apply to SIP Trunk providers.

Hosted PBX Providers: Many hosted PBX providers also advertise attractive prices when connecting your premise based telephone handsets to their IP/PBX over the Internet.  The same rules that apply to QoS and the Internet also apply to Hosted PBX Providers.

Many companies have attempted to violate the necessity of a managed network utilizing QoS when deploying VoIP.  If you plan on making your company suffer with less than acceptable voice quality, forcing management to come up with the budget necessary to purchase a managed network, you will not be the first to execute this strategy.  If your conscience prevents you from doing this, the following standards that will help you in achieving acceptable voice quality; a Service Level Agreement guaranteeing Latency of less than 100ms, Jitter of less than 20ms, and Packet loss of less than 1%.

QoS is essential to providing Business Class VoIP services and is more expensive to deploy than non-QoS networks. Although VoIP will work over the internet, it may not work to your satisfaction and there is very little that can be done to improve the quality short of signing new contracts for a managed network that recognizes the QoS tags.

Remember, if it is too good to be true, it is!  The extra money spent on quality will pay for itself in the long run.

Craig Hodges




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