Partitioning, Virtual Switches, and Multiple Control Planes

The controlled switch can have different physical cards with a number of interfaces. The network operator can partition the number of connections and the interface resources (by configuration performed in the controlled switch), such as bandwidth, VPI, and VCI ranges (assuming that the switch is an ATM switch, but it does not have to be an ATM switch). These partitioned resources can then be assigned to different controllers.

Examine Figure 1-6, an ATM switch that has five physical interfaces and two different controllers. The first two interfaces can be in a card, and the other interfaces can be in a different card. The controlled ATM switch also has an MPLS controller and a PNNI controller connected to it.

Figure 1-6. Multiservice Switch with Two Controllers

Figure 1-7 shows the resource partitioning and controller assignment in the ATM switch. These partitions of resources from the physical interface are called controlled interfaces from now on.

Figure 1-7. Resource Partitioning of the Interfaces

The first interface's resources are partitioned such that one third of the interface resources make an MPLS partition, and another third are assigned to a PNNI partition. The same thing happens with the switch's second interface. From the fourth interface, two-thirds of the resources are set aside for an MPLS partition. The total resources of the fifth interface are given to a PNNI partition.

NOTE

The third interface's resources are not assigned to any controller; therefore, from the controller's perspective, that interface does not exist.

To explicitly demonstrate the "ships in the night" concept, Figure 1-8 shows the visibility of the switch that each controller has. The MPLS controller "perceives" the switch as a box with three interfaces.

Figure 1-8. Virtual MPLS Switch

The MPLS controller does not make any distinctions as to whether the interfaces are in the same physical card or not. It believes the switch has three interfaces it can control and utilize with the given resources. This architecture relies on the separation between network information and specific hardware information.

This brings us to the next concept. The ATM switch is presented as a virtual switch to the controller, with only the interfaces partitioned for it (which are logical interfaces with generic resources).

Likewise, the ATM controlled switch is presented as a virtual switch to the PNNI controller, as shown in Figure 1-9.

Figure 1-9. Virtual PNNI Switch

In this application we can differentiate three switches:

• The physical switch with resources partitioned in the interfaces to be used by the control logic internal to the ATM switch (the one we mentioned that could not be physically separated). This control plane might or might not exist. If it does not exist, the resources not assigned to any controller are not used.

• A virtual switch presented to the MPLS controller.

• A virtual switch presented to the PNNI controller.

The MPLS virtual switch doesn't know about MPLS. It's completely oblivious. The controller based on the MPLS information controls the operation of the MPLS virtual switch (resources partitioned in the ATM switch), and the pair form a Label Switch Router (LSR) (discussed in more detail in Chapter 3, "Implementations and Platforms").