Prioritized classes: How to classify network traffic

Differentiated service identifies traffic as classes. The most common classes are defined using client IP addresses, application ports, server types, protocols, local IP addresses, and schedules. All the traffic that conforms to the same class is treated equally.

For more advanced classification, you can specify the application data to set different levels of service for some of your IBM i applications. Using application data is optional, but might be helpful when you want to classify at a lower level. There are two types of application data: application token or Uniform Resource Identifier (URI). If the traffic matches the token or URI that you specify in the policy, the policy is applied to the outbound response, thus giving the outbound traffic whatever priority is specified in the differentiated service policy.

Using application token with differentiated service policies

Using application data enables the policy to respond to the specific parameters (token and priority) passed by the application to the operating system through the sendmsg() application programming interface (API). This setting is optional. If you do not need this level of granularity in your outbound policies, select All tokens in the wizard. You can match an application's token and priority with a specific token and priority that are set in the outbound policy. In the policy, there are two parts to set the application data: the token and the priority.

  • What is an application token?

    An application token is a character string that can represent a defined resource, such as myFTP. The token you specify in the quality of service (QoS) policy is matched against the token provided by the outbound application. The application provides the token value through the sendmsg() API. If the tokens match, the application traffic is included in the differentiated service policy.

    To use an application token in a differentiated service policy, follow these steps:

    1. From the QoS configuration window, right-click DiffServ and select New Policy. Start the wizard.
    2. On the Server Data Request page, select Selected application token.
    3. To create a new token, click New. The New URI window opens.
    4. In the Name field, enter a meaningful name for the application token.
    5. In the URI field, delete the (/) and enter the application token (a string of not more than 128 characters). For example, myFTPapp, rather than the typical URI.
  • What is an application priority?

    The application priority you specify is matched against the application priority provided by the outbound application. The application provides the priority value using the sendmsg() API. If the priorities match, the application traffic is included in the differentiated service policy. All traffic defined in the differentiated service policy will still receive the priority given to the entire policy.

When you specify application token as the application data type, the application providing this information to the operation system must be specifically coded to use the sendmsg() API. This is done by the application programmer. The application's documentation should provide valid values (token and priority) that the QoS administrator uses in the differentiated service policy. The differentiated service policy then applies its own priority and classification to traffic that matches the token set in the policy. If the application does not have the values that match the values set in the policy, you must either update the application or use different application data parameters for the differentiated service policy.

Using a URI with differentiated service policies

When you create a differentiated service policy, the wizard allows you to set system data information, as discussed in the "Using application token with differentiated service policies" section. Although the fields in the wizard prompt you for an application token, you can instead specify a relative URI. Again, this is optional. If you do not need this level of granularity in your outbound policies, select All tokens in the wizard. You can match a specific URI set in the outbound policy.

The relative URI is actually a subset of an absolute URI (similar to the old absolute URL). Consider this example: http://www.ibm.com/software. The http://www.ibm.com/software segment is considered the absolute URI. The /software segment is the relative URI. All relative URI values must begin with one forward slash (/). The following segments are valid relative URI examples:

  • /market/grocery#D5
  • /software
  • /market/grocery?q=green

Before you set up a differentiated service policy that uses URIs, you must ensure that the application port assigned for the URI matches the Listen directive enabled for the fast response cache accelerator (FRCA) in the Web Server configuration. To change or view the port for your HTTP server, see Manage addresses and ports for HTTP Server.

FRCA identifies the URI for each outbound HTTP response. It compares the URI related to the outbound response to the URI defined in each differentiated service policy. The first policy with a token string (URI) that best matches the URI identified by FRCA is applied to all responses for the URI.