Quality of Service - History

History

Conventional Internet routers and LAN switches operate on a best effort basis. This equipment is less expensive, less complex and faster and thus more popular than competing more complex technologies that provided QoS mechanisms. There were four “Type of service” bits and three “Precedence” bits provided in each IP packet header, but they were not generally respected. These bits were later re-defined as DiffServ Code Points (DSCP) and are sometimes honored in peered links on the modern Internet.

With the advent of IPTV and IP telephony, QoS mechanisms are increasingly available to the end user.

A number of attempts for layer 2 technologies that add QoS tags to the data have gained popularity during the years, but then lost attention. Examples are Frame relay and ATM. Recently, MPLS (a technique between layer 2 and 3) have gained some attention. However, today Ethernet may offer QoS through its 802.1p. Ethernet is, by far, the most popular layer 2 technology.

In Ethernet, Virtual LANs (VLAN) may be used to separate different QoS levels. For example in fibre-to-the-home switches typically offer several Ethernet ports connected to different VLANs. One VLAN may be used for Internet access (low priority), one for IPTV (higher priority) and one for IP telephony (highest priority). Different Internet service providers may use the different VLANs.