Quality of Service (QoS) is what determines if a wireless technology can successfully deliver high value services such as voice and video. The chief detractors from good QoS are latency, jitter and packet loss. Solve these issue and you have a carrier-grade service. Very simply put, WiMAX offers a very low latency across the wireless span. Most ven-dors have products where latency is less than 10 milliseconds from base station to CPE (and vice versa). To put this in perspective, latency must be measured end-to-end. VoIP, for example, is highly susceptible to latency. If latency exceeds 150 milliseconds for ex-ample, the quality of the conversation begins to drag. At or above 200 milliseconds many listeners may find a conversation unintelligible.
In the case of WiMAX, the large majority of latency will not occur on the air link be-tween subscriber and base station but rather on the wired portion of the connection between the subscriber and what ever the "other end" might be (web site server, IPTV server or VoIP called party). The figure below illustrates how any latency on the wireless portion of a network is minimal relative to that on the wired portion of a network.
Figure 26: Over-the-air latency in a WiMAX network is minimal relative to the latency on the IP backbone or the rest of the network
Prioritizing Traffic
The chief solution in offering good QoS is to prioritize time sensitive traffic such as VoIP and video. Fixed WiMAX offers 4 categories for the prioritization of traffic and mobile WiMAX has 5 categories:
| Service Class | Applications | QOS Specifications |
| Unsolicited Grant Service (UGS) | VoIP | -Jitter tolerance -Maximum latency tolerance -Maximum sustained rate |
| Real-time Packet Services (rtPS) | Streaming Audio/Video | -Traffic priority -Maximum latency tolerance -Maximum reserved rate -Maximum sustained rate |
| Extended real time Packet Services (ertPS) | VoIP (VoIP with Activity Detection | -Traffic priority -Jitter tolerance -Maximum latency tolerance -Maximum reserved rate -Maximum sustained rate |
| Non-real time Packet Services (nrtPS) | FTP | -Traffic priority -Maximum reserved rate -Maximum sustained rate |
| Best Effort (BE) | Data transfer, web browsing | -Traffic priority -Maximum sustained rate |
Early Wi-Fi offered no prioritization of traffic and the technology has not gone beyond the wireless local area network (WLAN) stage. WiMAX is different in that, in the case of fixed WiMAX, there are four categories of traffic prioritized per their needs in delivery with VoIP and video at the top and web surfing at the bottom. Mobile WiMAX offers 5 such prioritized categories with VoIP being top priority.
