To implement quality of service, you analyze network traffic to determine any broad groupings into which the traffic can be divided. Then, you organize the various groupings into classes of service with individual characteristics and individual priorities. Classes of service form the basic categories on which you base the QoS policy for your organization and represent the traffic groups that you want to control.
When analyzing network traffic, consider the following guidelines:
Does your company offer service-level agreements to customers?
If yes, then evaluate the relative priority levels of the SLAs that your company offers to customers. The same applications might be offered to customers who are guaranteed different priority levels.
For example, your company might offer web site hosting to each customer, which indicates that you need to define a class for each customer web site. One SLA might provide a premium web site as one service level. Another SLA might offer a “best-effort” personal web site to discount customers. This factor indicates not only different web site classes but also potentially different per-hop behaviors that are assigned to the web site classes.
Does the IPQoS system offer popular applications that might need flow control?
You can improve network performance by enabling IPQoS on servers offering popular applications that generate excessive traffic. Common examples are electronic mail, network news, and FTP. Consider creating separate classes for incoming and outgoing traffic for each service type, where applicable. For example, you might create a mail-in class and a mail-out class for the QoS policy for a mail server.
Does your network run certain applications that require highest-priority forwarding behaviors?
Any critical applications that require highest-priority forwarding behaviors must receive highest priority in the router's queue. Typical examples are streaming video and streaming audio.
Define incoming classes and outgoing classes for these high-priority applications. Then, add the classes to the QoS policies of both the IPQoS-enabled system that serves the applications and the Diffserv router.
Does your network experience traffic flows that must be controlled because the flows consume large amounts of bandwidth?
Use netstat, snoop, and other network monitoring utilities to discover the types of traffic that are causing problems on the network. Review the classes that you have created thus far, and then create new classes for any undefined problem traffic category. If you have already defined classes for a category of problem traffic, then define rates for the meter to control the problem traffic.
Create classes for the problem traffic on every IPQoS-enabled system on the network. Each IPQoS system can then handle any problem traffic by limiting the rate at which the traffic flow is released onto the network. Be sure also to define these problem classes in the QoS policy on the Diffserv router. The router can then queue and schedule the problem flows as configured in its QoS policy.
Do you need to obtain statistics on certain types of traffic?
A quick review of an SLA can indicate which types of customer traffic require accounting. If your site does offer SLAs, you probably have already created classes for traffic that requires accounting. You might also define classes to enable statistics gathering on traffic flows that you are monitoring. You could also create classes for traffic to which you restrict access for security reasons.
For example, a provider might offer platinum, gold, silver, and bronze levels of service, available at a sliding price structure. A platinum SLA might guarantee top priority to incoming traffic that is destined for a web site that the ISP hosts for the customer.
For an enterprise, you might create classes of service such as the following examples:
Popular applications such as email and outgoing FTP to a particular server, either of which could constitute a class. Because employees constantly use these applications, your QoS policy might guarantee email and outgoing FTP a small amount of bandwidth and a lower priority.
An order-entry database that needs to run 24 hours a day. Depending on the importance of the database application to the enterprise, you might give the database a large amount of bandwidth and a high priority.
A department that performs critical work or sensitive work, such as the payroll department. The importance of the department to the organization would determine the priority and amount of bandwidth you would give to such a department.
Incoming calls to a company's external web site. You might give this class a moderate amount of bandwidth that runs at low priority.