Quality of Service (QoS) is a feature on routers, switches, and many access points. QoS prioritizes traffic so that more important traffic can pass first. The result is a performance improvement for critical network traffic. QoS equipment is useful with VoIP phones and streaming video, or in LANs with high volumes of local traffic.
On routers, traffic can be prioritized according to QoS information received, and the default QoS for selected services can be overridden.
QoS varies by switch. The higher the level switch, the higher the network application layer the switch can work with. The number of queues differ, as well as the type of information that is used to prioritize the traffic.
- Most unmanaged switches do not use or change QoS. The traffic passes unaltered, with the exception of some models, which can honor priority tags.
- Smart Switches allow setting QoS by port to a high, medium, or normal queue.
- In addition, Layer 2 managed switches both set and honor Differentiated Services (DiffServ) packet tagging.
- In addition, Layer 3 switches let you define access control lists (ACLs) that can recognize and then manipulate traffic types.
QoS for NETGEAR products is "best effort," meaning that bandwidth for high priority services is not 100% reserved, so low priority services cannot be locked out of network access.
A key to optimizing networks is to correct any severe bottlenecks. When the bottleneck is a router or a switch, QoS is likely to help. Here are guidelines to decide whether QoS might be useful:
- The speed of the Internet is lower than LAN speeds a typical user can achieve. Therefore, if the worst bottleneck is your Internet connection — outside of your equipment — QoS will not help it.
- The amount of traffic and available bandwidth from your LAN to the Internet is usually less than amount of traffic and available bandwidth coming to your LAN. ISPs give less outgoing bandwidth intentionally, for economy, because most users upload less than they download from the Internet. Therefore, QoS on routers is most useful for traffic that leaves your LAN. For incoming traffic, any useful QoS has probably already been applied by your ISP.
- NETGEAR switches pass traffic so quickly, that in high volume situations, a router to the Internet is overburdened with traffic. Adding a QoS switch to work with your existing QoS router will not improve your Internet performance. On the other hand, if your LAN has many users sending a heavy traffic load within your LAN, a QoS switch might very well help local performance.
Just as a chain always has a "weakest link", a network always has a bottleneck. Users find some bottlenecks more important than others. If you don't mind a slow printer connection, it's not a problem for you. The bottleneck that QoS solves is a high volume of traffic coming through a router or switch, in situations where some types of traffic are always more urgent than other types.