By Richard Nesin, president, HomePNA
In the June 4th post QoS part 1 we jumped into the middle of a discussion on Quality of Service (QoS). If you recall, QoS is a mechanism used to provide reliable and predictable delivery of real-time data such as IPTV and VoIP streams over a home network that is carrying other “best-effort” data like porn (you are enabling those parental controls, right?). To techies, home network Quality of Service (QoS) used to means priority-based QoS, the original QoS provided by Wi-Fi home networks.
So where does the “priority” in Priority QoS come from? It comes from the
Data sent over a network is broken into same-size pieces called “packets,” which are like the way the words in a book are broken into pages. Information is attached to each packet to tell the network equipment things like the size of the packet, where the packet comes from, and where it’s going – this is called the packet “header.”
Header information helps network equipment to route the packet from its source, say a server at You Tube, to its destination, say your PC. Included in this header are three “priority bits.” (You’ve probably guessed where this is going, right?) Three priority bits enable eight levels of priority although sometimes only four are used. Real-time data such as video is usually given a high priority and non-real-time “best-effort data” is given low priority. Network equipment uses various techniques to insure the delivery of high-priority data over low priority. Priority QoS, also called Class of Service (CoS), will prioritize one type of data over another but typically won’t help when two same-priority data streams are being sent simultaneously.