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Configuring CoS to Manage VoIP Traffic When Running MX Series Router Cloud CPE Services

In this example you configure a multifield classifier (firewall filter) called voip-filter, which is applied to the MX Series PE router on ingress interface ge-1/2/3, logical interface 33. This interface connects the subscriber router to the PE router. The firewall filter examines incoming packets and prioritizes any Session Initiation Protocol (SIP) and Real-Time Transport Protocol (RTP) VoIP traffic by examining incoming IPv4 packets for the following criteria:

  • Terms=SIP and RTP

  • Protocols=UDP and TCP

  • From port=5060

When a match on all three of these criteria is found, the router accepts the packet and sends it to a high-priority forwarding-class called cos-voice, which uses transmit queue 4. The cos-voice forwarding-class and an egress scheduler called sip-voip-scheduler, are mapped to a scheduler map called sip-voip-sched-map, which you apply to egress interface ge-1/1/1. The scheduler map ensures the SIP and RTP packets receive a high priority and transmit rate.

Note:

This topic does not show a complete configuration; it shows how to configure only the PE router for this class of service example. Core router or subscriber router configurations are beyond the scope of this topic. To ensure end-to-end quality of service (QoS), you must configure class of service parameters on each device in the network path.

This example uses the following topology:

Note:

This example requires the following interfaces on the MX Series router:

  • Modular Port Concentrators (MPCs) line modules with the hierarchical class of service (H-CoS) option enabled.

Before you begin, complete the following steps:

Complete the following tasks to configure class of service to manage VoIP traffic for MX Series router cloud CPE services:

Example: Configuring Class of Service for MX Series Router Cloud CPE Services

Complete the following tasks to configure class of service for MX Series router cloud CPE services:

Configure a Forwarding Class to Classify SIP VoIP Traffic

Configure VoIP traffic to be classified to the corresponding forwarding class:

  1. Access the class of service forwarding class configuration hierarchy and specify the name of the forwarding class.
  2. Specify a high priority and queue number for the forwarding class.
  3. Verify the configuration.
  4. Save your configuration.

Configure the Scheduler for SIP VoIP Traffic

To configure a scheduler to properly prioritize the SIP VoIP traffic:

  1. Access the scheduler configuration hierarchy and specify a name for the SIP VoIP scheduler.
  2. Specify the buffer size for the queue. To ensure that the queue handling the SIP VoIP traffic receives the highest priority, set the buffer size to 96 percent.
  3. Specify the priority of the scheduler. For example, to ensure the SIP VoIP traffic receives the highest priority, set the priority to strict-high.
  4. Specify the transmission rate for SIP VoIP traffic. In this example, set the transmission rate to 70 percent.
  5. Review the configuration.
  6. If the configuration looks correct, save it.

Configure the Scheduler Map

After defining the scheduler, you can associate it with a specified forwarding class by including it in a scheduler map.

To associate the scheduler and forwarding class:

  1. At the configuration hierarchy, specify a name for the scheduler map.
  2. Create the mapping between the cos-voice forwarding class and the sip-voip-scheduler.
  3. Review the configuration.
  4. If the configuration looks correct, save it.

Apply the Scheduler Map to the Egress Interface

After you have defined the scheduler map, you must apply it to the output interface. For example:

  1. From the class-of-service configuration hierarchy, specify the name of the output interface.
  2. Apply the scheduler map to the output interface.
  3. Review the configuration.
  4. If the configuration looks correct, save it.

Example: Configuring and Applying the Multifield Classifier

Configure the Firewall Filter to Classify SIP Traffic

To configure an IPv4 firewall filter to classify session initiation protocol (SIP) VoIP traffic to a named forwarding class:

  1. Configure an IPv4 firewall filter named voip-filter that checks for packets from the UDP protocol.
  2. Configure the same IPv4 firewall filter to check for packets from the TCP protocol.
  3. Specify which port to use for UDP and TCP traffic.
  4. Classify the UDP and TCP packets to the cos-voice forwarding class.
  5. Specify that packets matching the filter conditions are accepted.
  6. Verify the configuration.

Configure the Firewall Filter to Classify RTP Traffic

This procedure configures an IPv4 firewall filter to classify Real-Time Transport Protocol (RTP) VoIP traffic to the cos-voice forwarding class.

  1. Configure an IPv4 firewall filter that checks for packets from the UDP protocol.
  2. Specify which port is used for UDP and TCP traffic.
  3. Classify the UDP and TCP packets to the named forwarding class. Specify the same forwarding class you configured for SIP traffic.
  4. Specify that packets matching the filter conditions are accepted.
  5. Verify the configuration.
  6. If the configuration looks correct, save it.

Apply the Firewall Filter to the Ingress Interface

To apply the firewall filter to the ingress interface:

  1. Navigate to the interface to which you want to apply the firewall filter.
  2. Apply the filter as an input filter.
  3. Verify the entire configuration.
  4. If the configuration looks correct, save it.