Traffic shaping

Apr 18, 2018

Traffic shaping allows you to regulate the network traffic flow to assure a certain level of quality of service (QoS). You can regulate the flow of packets into a network (bandwidth throttling) or out of a network (rate limiting).

Using traffic shaping policies you can set the priority of different link traffic and send traffic onto the link at a rate close to, but no greater than, the link speed. Unlike acceleration, which applies only to TCP/IP traffic, the traffic shaper handles all traffic on the link.

You can set high bandwidth for traffic flows that are considered more important than the rest of the traffic flows, allowing you to optimally use the scarce link resources.

The traffic shaping is based on weighted fair queuing, which gives each service class its fair share of the link bandwidth. If the link is idle, any connection (in any service class) can use the entire link. When multiple connections are competing for the link bandwidth, the traffic shaper applies traffic shaping policies to determine the right mix of traffic.

For information on Weighted Fair Queuing, see Weighted Fair Queuing.

To configure traffic shaping:

  1. Configure the Link definition.

    The Link definition is used by the traffic shaper to determine the send and receive link speed and other link related information. For more information on how traffic shaper uses link definition and how to configure link definitions, see Link Definitions.

  2. Configure the Application definition.

    The traffic flowing through the link is examined by the application classifier to determine which application it belongs to and then the application is looked up in the service class list to determine which service class it belongs to. For more information on application classification and how to configure application definition see Traffic Classification.

  3. Create a traffic shaping policy.

    You can use the default traffic shaping policies or create a new policy to set the weighted priority and other parameters as per your network requirements. For information on creating traffic shaping policy, see Traffic Shaping Policies.

  4. Configure a service class definition and associate the traffic shaping policy to the service class.

    For information on configuring service class definition, see Service Classes.

Some highlights of the traffic shaper:

  • All WAN traffic is subject to traffic shaping: accelerated connections, unaccelerated connections, and non-TCP traffic such as UDP flows and GRE streams.

  • The algorithm is weighted fair queuing, in which the administrator assigns each service class a priority. Each service class represents a bandwidth pool, entitled to a minimum fraction of the link speed, equal to (my_priority/sum_of_all_priorities). A service class with a weighted priority of 100 gets twice as much bandwidth as a service class with a weighted priority of 50. You can assign weights from 1 through 256.

  • Each connection within a service class gets an equal share of the bandwidth allotted to that service class.

  • Each connection gets its fair share of the link bandwidth, because priorities are applied to the actual WAN data transferred, after compression. For example, if you have two data streams with the same priority, one achieving 10:1 compression and the other achieving 2:1 compression, users see a 5:1 difference in throughput, even though the WAN link usage of the two connections is identical. In practice, this disparity is desirable, because WAN bandwidth, not application bandwidth, is the scarce resource that needs to be managed.

  • Traffic-shaping policies apply equally to both accelerated and unaccelerated traffic. For example, an accelerated Virtual Apps connection and an unaccelerated Virtual Apps connection both receive traffic shaping, so both can have an elevated priority compared to bulk traffic. As another example, time-sensitive non-TCP traffic, such as VoIP (which uses the UDP protocol) can be expedited.

  • Traffic shaping is applied to the WAN link in both the sending and receiving directions, to both accelerated and non-accelerated traffic. This feature prevents congestion and increased latency even when the other side of the link is not equipped with a Citrix SD-WAN WANOP appliance. For example, Internet downloads can be prioritized and managed.

  • The traffic-shaping policy for a service class can be specified on a per-link basis if desired.

  • In addition to shaping the traffic directly, the traffic shaper can affect it indirectly by setting the Differentiated Services Code Point (DSCP) field to inform downstream routers about the type of traffic shaping each packet requires.

Traffic shaping