3Com 10014299 manual Frame Relay Queueing Management, Frame Relay Traffic Policing

260CHAPTER 17: CONFIGURING FRAME RELAY

notification (BECN) flag bit is 1, indicating that the congestion has occurred to the network, and the transmit rate of the PVC will be lowered to CIR.

Frame Relay Queueing Management

To ensure that the packets on the PVCs can be transmitted at an average rate in the process of Frame Relay traffic shaping, a queueing mechanism should be adopted to manage the packets. Generally, except that the Frame Relay interface owns one interface queue, the Frame Relay PVC does not have its own transmit queue. However, after the Frame Relay traffic shaping is enabled on the Frame Relay interface, all the PVCs belonging to this interface will own their independent queues, and all the packets t transmitted from the PVCs will enter the Frame Relay PVC queues first.

Besides the Frame Relay PVC queues, the Frame Relay interface also owns an interface queue. In the case that the Frame Relay traffic shaping is not enabled, there will only be the Frame Relay interface queue. After it is enabled, both Frame Relay PVC queues and the Frame Relay interface queue will exist. Their relations are illustrated in Frame Relay queueing.

Figure 84 Frame Relay queueing

PVC Queue

Interface queue

The Frame Relay PVC queueing types include FIFO (First-In First-Out Queueing), PQ (Priority Queueing), CQ (Custom Queueing), and WFQ (Weighted Fair Queueing).

The FIFO, PQ, CQ, WFQ, and PIPQ (PVC Interface Priority Queueing) queues can be used on a Frame Relay interface. Among them, FIFO, PQ, CQ, and WFQ queues are general queues. For the detailed introduction, refer to the part of QoS. PIPQ can only be applied on the Frame Relay interface. It is similar to PQ, but aiming at the PVCs on an interface. When the Frame Relay traffic shaping is enabled on an interface, the queueing type on the interface can only be either FIFO or PIPQ.

PIPQ is applied on a Frame Relay interface. There are four types of PIPQ: top, middle, normal and bottom. Their queueing priorities are listed in descending order. The packets on the same PVC can only enter one type of PIPQ queue, and the packets on different PVCs enter different PIPQ queues on the interface, depending on the priorities of the PVCs. The PIPQ transmitting policy is as follows: Based on the queueing priority, transmit the packets in the queue with low priority after those in the queue with high priority are transmitted.

Frame Relay Traffic Policing

Frame Relay policing monitors the traffic that flows into the network from each PVC, and restricts it in a certain range. If the traffic size on a PVC exceeds the range set by the user, the router will adopt the measures like discarding the packets, so as to protect the network resources and the profit of the operator.