Substitute Diffserv Values

The Differentiated Services (Diffserv) standard outlines an approach for giving precedence to specific traffic types, providing a scalable solution to managing traffic. If you have classified traffic by Diffserv, you can change the precedence or service level of an application by creating policies to change the code point value or substitute different COS/TOS values.

For information on creating classes based on Diffserv values, see Classify Diffserv Code Point Traffic and Classify Diffserv COS/TOS Traffic. For Diffserv details, see RFC 2474 at http://ietf.org/rfc.html.

Diffserv is an option that is available in both rate and priority policies.

Substituting a Diffserv Code Point Value

Note: To perform this task from PolicyCenter, you must first select a group and/or unit configuration from the Group: and Unit: drop-down lists at the top of the page.

To substitute a different code point value:

1. Open the priority or rate policy. (See Modify a Policy.)

2. Click diffserv in the Policy window. The Policy:DiffServ window opens.  show screen

3. Make sure Code Point is selected for the Diffserv Type.

4. Select Changed to and enter a value (0-63) in the text box.

5. Click OK.

6. Click apply changes in the Policy window.

Substituting a Diffserv COS/TOS Value

The COS/TOS Diffserv option lets you override a packet's Type of Service (TOS) value before forwarding an IP packet, thus controlling the priority when it reaches the router.

To override a packet's precedence before forwarding the packet, thus controlling the priority when it reaches the router, use IP precedence class-of-service (COS) substitution and specify a preference level.

Using TOS substitution, you can reassign the service level for an application, based on your business perspective. For example, interactive applications with small data packets (for example, Telnet) usually require a minimum delay, while file transfer applications like FTP require maximum throughput.

To specify a COS/TOS substitution:

1. Open the priority or rate policy. (See Modify a Policy.)

2. Click diffserv in the Policy window. The Policy:DiffServ window opens.

2. Choose COS/TOS for the Diffserv Type.  show screen

3. For IP Precedence Substitution, select Changed to and select an IP precedence (COS) value from 0 to 7, where 7 is the highest precedence.

4. For Type of Service Substitution, select Changed to and enter a TOS value.

5. Click OK.

6. Click apply changes in the Policy window.