One of the most challenging parts of using PacketWise is the selection and use of appropriate policies.
The following are some guidelines to follow:
1. Many traffic classes offer suggested polices. These give a good starting point, but are generic. It's helpful to understand the different types of policies and how they should be used. When creating a new policy, simply select the suggest policy button. (If the class already has a policy, the button will not appear. To get it back simply delete the policy, then add a new one.)
2. Rate policies invoke Packeteer's TCP Rate Control technology. They are appropriate for most types of IP traffic, in particular applications that are bursty in nature (such as HTTP, FTP) or require specific bandwidth guarantees (such as VoIP), and to control inbound traffic. Rate is the most commonly used type of policy and is appropriate for most types of TCP and UDP traffic.
3. When in doubt, the best policy to use is rate, guaranteed 0, burstable at priority 3, with no limit. This will assure that Rate Control is invoked so that the PacketWise can achieve inbound control on the flow.
4. Priority policies use the more traditional prioritized queuing-based approach. Priority policies are best for:* non-IP traffic such as IPX * very short flows such as DNSIf a flow is known to only last for 2 or 3 packets, then there is not much reason to spend effort rate controlling it, so select a priority policy. DNS is a good example.
Unpredictable, low-bandwidth TCP traffic such as Telnet also benefits from a priority policy. Telnet is usually fairly high priority because of its interactive nature, so a priority of 5 or 6 is recommended. (Telnet is considered unpredictable because it does not send a packet until the user presses a key. The delay in milliseconds between key presses varies every time. By contrast, most traffic types, such as FTP and HTTP, are considered predictable because they send a whole file at once with no arbitrary pauses between packets.)
5. You don't need to assign policies to every traffic class. If you don't assign a specific policy to a class, it inherits the policy of the Default class, which is Priority 3.
6. The easiest approach is to assign policies to increase priority and/or reserve bandwidth for your mission critical traffic. These are usually few in number and the customer has a good idea what they are. They may have already been found by traffic discovery, or you may need to use tools like top-talkers/listeners and custom classes to identify.
7. You can also assign policies to de-prioritize and/or limit low priority traffic. For more specific information, see Policy/Partition Guidelines in PacketGuide.
Things to Remember about Policies
* Rate policies have two components: guaranteed bandwidth and burstable bandwidth. Bandwidth is allocated to each individual user session. You must be very careful not to assign large amounts of guaranteed bandwidth, because as the number of simultaneous sessions increases, you'll run out of bandwidth. (When this happens, you'll see guaranteed rate failures in the Monitor Traffic screen.)
* For rate policies, it is generally recommended to assign 0 bps guaranteed bandwidth, burstable at the appropriate priority level to some limit (which will just be the link/partition size if you leave it blank). Once you have a good understanding of the number of sessions on the network and a requirement to guarantee a specific service level, you can start adjusting the amount of guaranteed bandwidth to get the desired result.
* Guaranteed policies do lend out unused bandwidth to other flows.