Adding more bandwidth cannot solve every network performance issue. Any network connection, when fully utilized, will cause communications to slow down while the router is forced to queue outgoing traffic. This often happens with an Internet or WAN connection because traffic from multiple clients on a high-speed LAN must share a lower-speed connection. s
For example, if an organization has a 1000 Mbps LAN and a 10 Mbps Internet connection, computers can send requests across the LAN to the router much faster than the router can forward the requests to the Internet. In this scenario, the router has to hold the outgoing requests in a queue and send each request when more bandwidth is available. By default, routers send outgoing traffic from the queue in a first-in, first-out basis. Therefore, critical traffic might be waiting in the queue behind less critical traffic.
Figure 3 shows two clients sending traffic to two Web sites: www.contoso.com (a critical internal Web site) and www.southridgevideo.com (a non-critical personal Web site). As the figure demonstrates, the router treats the packets exactly the same, and packets destined for www.southridgevideo.com might be sent after packets destined for www.contoso.com.
Figure 3 Without QoS, low-priority traffic can be sent before high-priority traffic
When IT professionals configure Quality of Service (QoS), Windows marks outgoing packets with a Differentiated Services Code Point (DSCP) number. Routers then examine the DSCP value to determine the packet’s priority. If a network connection is fully utilized and the router is holding packets in a queue, higher-priority packets are sent before lower-priority packets, overriding the default first-in, first-out behavior. Therefore, QoS can maintain the responsiveness of critical network applications even when the network is busy.
With earlier versions of Windows, IT professionals could specify applications, IP addresses, and port numbers to determine QoS priorities. With this level of detail, IT professionals could prioritize database traffic over Web and e-mail traffic—a useful capability. They could also prioritize traffic to a critical server over traffic to a less-critical server.
However, with the growth of Web services and application server consolidation, IT professionals need finer control over how Windows prioritizes Web traffic. For example, a single intranet server might host a critical customer service application and a non-critical discussion forum on the same server. Web services or applications on a single server share a common IP address, limiting the value of IP-based prioritization. IT professionals need to be able to assign different priorities to different Web applications and sites on a single server.
Windows 7 allows IT professionals to prioritize Web traffic based on the URL. With URL-based QoS, IT professionals can ensure important Web traffic is processed before less-important traffic, improving performance on busy networks. For example, IT professionals can assign Web traffic for critical internal Web sites a higher priority than external Web sites, maximizing performance when the network is busy. Similarly, if users visit non-work-related Web sites that consume a large portion of the network’s bandwidth, IT professionals can assign that traffic a low priority so other traffic isn’t impacted.
With URL-based QoS, IT professionals can also configure the path portion of a URL, known as the Uniform Resource Identifier (URI). For example, IT professionals could assign http://contoso.com/cust_serv/ a high priority and http://contoso.com/forum/ a low priority. IT professionals can configure QoS using Group Policy settings.
Figure 4 URL-based QoS allows IT professionals to prioritize Web traffic