Bandwidth Oversubscription Overview
LSPs are established with bandwidth reservations configured for the maximum amount of traffic you expect to traverse the LSP. Not all LSPs carry the maximum amount of traffic over their links at all times. For example, even if the bandwidth for link A has been completely reserved, actual bandwidth might still be available but not currently in use. This excess bandwidth can be used by allowing other LSPs to also use link A, oversubscribing the link. You can oversubscribe the bandwidth configured for individual class types or specify a single value for all of the class types using an interface.
You can use oversubscription to take advantage of the statistical nature of traffic patterns and to permit higher utilization of links.
The following examples describe how you might use bandwidth oversubscription and undersubscription:
- Use oversubscription on class types where peak periods of traffic do not coincide in time.
- Use oversubscription of class types carrying best-effort traffic. You take the risk of temporarily delaying or dropping traffic in exchange for making better utilization of network resources.
- Give different degrees of oversubscription or undersubscription
of traffic for the different class types. For instance, you configure
the subscription for classes of traffic as follows:
- Best effort—ct0 1000
- Voice—ct3 1
When you undersubscribe a class type for a multiclass LSP, the total demand of all RSVP sessions is always less than the actual capacity of the class type. You can use undersubscription to limit the utilization of a class type.
The bandwidth oversubscription calculation occurs on the local router only. Because no signaling or other interaction is required from other routers in the network, the feature can be enabled on individual routers without being enabled or available on other routers which might not support this feature. Neighboring routers do not need to know about the oversubscription calculation, they rely on the IGP.
The following sections describe the types of bandwidth oversubscription available in the Junos OS:
- LSP Size Oversubscription
- Link Size Oversubscription
- Class Type Oversubscription and Local Oversubscription Multipliers
