4.4.4.3 HERRAMIENTAS DE EVALUACIÓN

This section describes the QoS features you configure for the PPP link.Most of these QoS features are the same as those that you configure for a PPP 64-K link, a Frame Relay 64-K link, and a Frame Relay T1 link. Therefore, instead of repeating conceptual information, these steps refer to the related 64-K Frame Relay sections that fully cover background information for these features common to all configurations.

Note This configuration process provides two alternative ways of configuring strict priority queueing for VoIP traffic. In this set of steps, both methods are presented as Step 2. The first Step 2 shows how to configure strict priority using IP RTP Priority. The second, (alternative) Step 2 shows how to configure strict priority queueing using strict priority within CBWFQ.

Step 1: Configure CRTP for the T1 PPP Link

To enable RTP header compression, perform the following task in interface configuration mode (you need to enable compression on both ends of the connection):

For background information on CRTP, see “Step 1: Configure CRTP for a 64-K Frame Relay Link” earlier in this chapter. Also, see Chapter 2, “About QoS Features for Voice.”

Command Purpose

Step 2: Configure WFQ and Enable the Strict Priority Queue for VoIP Packets on the T1 PPP Link

When WFQ is enabled, it creates a strict priority queue that exists potentially for use by delay-sensitive traffic such as voice traffic. However, the strict priority queue cannot be used until it is enabled through configuration of the ip rtp priority command. This section gives the command syntax for the

fair-queue and ip rtp priority commands that you use to enable WFQ and its strict priority queue.

To enable weighted fair queueing for the PPP interface shown in Example 3-4, set the congestion threshold after which messages for high-bandwidth conversations are dropped, and specify the number of dynamic and reservable queues, perform the following task in interface configuration mode after specifying the interface:

To reserve a strict priority queue for a set of RTP voice packet flows belonging to a range of UDP destination ports, use the following command in interface configuration mode:

For background information on WFQ and the strict priority feature, see the “Step 2: Configure WFQ and Enable the Strict Priority Queue for VoIP Packets on the PPP Link” earlier in this chapter. Also, see Chapter 2, “About QoS Features for Voice.”

Step 2: Alternative Configuration: Configure WFQ and Enable the Strict Priority Queue within CBWFQ

This step provides an alternative method of giving voice traffic strict priority queueing. It describes how you can use the same feature described in the first Step 2, but within CBWFQ to apply strict priority queueing to a CBWFQ class used for voice traffic.

Command Purpose

fair-queue 64 256 0 Configures the PPP interface to use weighted fair queueing with a congestive discard threshold of 64, 256 dynamic queues, and no reservable queues.

Command Purpose

ip rtp priority 16384 16383 288 Reserves a strict priority queue for the VoIP packet flow using destination ports in the range of 16384 and 16383. VoIP flows for the example PPP link whose UDP

destination ports are within the range of 16384 and 16383 are granted strict priority with a bandwidth guarantee of 48 kbps.

The example configuration is designed to service 4 voice calls at the cost of 12 kbps per call. For your configuration, assume that each call consumes 12 K and set the bandwidth parameter to the result of the following equation:

bandwidth = 12 K x number-of-calls

The IP RTP Priority feature does not require that you know the port of a voice call. Rather, the feature gives you the ability to identify a range of ports whose traffic is put into the priority queue. Moreover, you can specify the entire voice port range—16384 to 32767—to ensure that all voice traffic is given strict priority service.

Priority queueing within CBWFQ enables use of the strict priority queue implicit to WFQ. Although it is possible to enqueue various types of real-time traffic to the strict priority queue, it is strongly recommended that you direct only voice traffic to it. This recommendation is made because voice traffic is well-behaved, whereas other types of real-time traffic are not. Moreover, voice traffic requires that delay be nonvariable in order to avoid jitter. Real-time traffic such as video could introduce variation in delay thereby thwarting the steadiness of delay required for successful voice traffic transmission. For complete information the Priority Queueing within CBWFQ feature, see Chapter 2, “QoS Features for Voice over IP.”

This section gives the command syntax for the fair-queue and ip rtp priority commands that you use to enable WFQ and its strict priority queue.

To enable weighted fair queueing for the PPP interface shown in Example 3-4, set the congestion threshold after which messages for high-bandwidth conversations are dropped, and specify the number of dynamic and reservable queues, perform the following task in interface configuration mode after specifying the interface:

To create a class for voice called “class voice” and configure that class as a strict priority class with a bandwidth allocation of 288 kbps, use the following commands beginning in interface configuration mode: