Frame Relay IP RTP Priority

This feature extends the functionality offered by the ip rtp priority command by supporting Frame Relay PVCs. This feature allows you to specify a range of User Datagram Protocol (UDP) ports whose voice traffic is guaranteed strict priority service over any other queues or classes using the same output interface. Strict priority means that if packets exist in the priority queue, they are dequeued and sent first---that is, before packets in other queues are dequeued.

Command	Purpose
Router(config-map-class)#frame-relay ip rtp priority starting-rtp-port-number port-number-range bandwidth	Reserves a strict priority queue for a set of RTP packet flows belonging to a range of UDP destination ports.

NoteBecause the frame-relay ip rtp priority command gives absolute priority over other traffic, it should be used with care. In the event of congestion, if the traffic exceeds the configured bandwidth, then all the excess traffic is dropped.

Syntax Description

starting-rtp-port-number	The starting UDP port number. The lowest port number to which the packets are sent.
port-number-range	The range of UDP destination ports. Number, which added to the starting-rtp-port-number, yields the highest UDP port number.
bandwidth	Maximum allowed bandwidth (in kbps).

Defaults

This command has no default behavior or values.

Command Modes

Map-class configuration

Command History

Release	Modification
12.0(7)T	This command was introduced.

Usage Guidelines

This command is most useful for voice applications, or other applications that are delay-sensitive. To use this command, you must first enter the map-class frame-relay command. After the Frame Relay map class has been configured, it must then be applied to a PVC.

This command extends the functionality offered by the ip rtp priority command by supporting Frame Relay PVCs. The command allows you to specify a range of UDP ports whose voice traffic is guaranteed strict priority service over any other queues or classes using the same output interface. Strict priority means that if packets exist in the priority queue, they are dequeued and sent first---that is, before packets in other queues are dequeued.

Frame Relay traffic shaping (FRTS) and Frame Relay Fragmentation (FRF.12) must be configured before the frame-relay ip rtp priority command is used.

Compressed RTP (CRTP) can be used to reduce the bandwidth required per voice call. When using CRTP with Frame Relay, you must use the encapsulation frame-relay cisco command instead of the encapsulation frame-relay ietf command.

Remember the following guidelines when configuring the bandwidth parameter:

• It is always safest to allocate to the priority queue slightly more than the known required amount of bandwidth, to allow room for network bursts.

• The IP RTP Priority admission control policy takes RTP header compression into account. Therefore, while configuring the bandwidth parameter of the ip rtp priority command you only need to configure for the bandwidth of the compressed call. Because the bandwidth parameter is the maximum total bandwidth, you need to allocate enough bandwidth for all calls if there will be more than one call.

• Configure a bandwidth that allows room for Layer 2 headers. The bandwidth allocation takes into account the payload plus the IP, UDP, and RTP headers but does not account for Layer 2 headers. Allowing 25 percent bandwidth for other overhead is conservative and safe.

• The sum of all bandwidth allocation for voice and data flows on an interface cannot exceed 75percent of the total available bandwidth, unless you change the default maximum reservable bandwidth. To change the maximum reservable bandwidth, use the max-reserved-bandwidth command on the interface.

Examples

The following example first configures the Frame Relay map class called voip and then applies the map class to PVC 100 to provide strict priority service to matching RTP packets:

map-class frame-relay voip
 frame-relay cir 256000
 frame-relay bc 2560
 frame-relay be 600
 frame-relay mincir 256000
 no frame-relay adaptive-shaping
 frame-relay fair-queue
 frame-relay fragment 250
 frame-relay ip rtp priority 16384 16380 210
 
interface Serial5/0
 ip address 10.10.10.10 255.0.0.0
 no ip directed-broadcast
 encapsulation frame-relay
 no ip mroute-cache
 load-interval 30
 clockrate 1007616
 frame-relay traffic-shaping
 frame-relay interface-dlci 100
  class voip
 frame-relay ip rtp header-compression
 frame-relay intf-type dce
 

In this example, RTP packets on PVC 100 with UDP ports in the range 16384 to 32764 will be matched and given strict priority service.

Related Commands

Command	Description
ip rtp priority	Reserves a strict priority queue on a Frame Relay PVC for a set of RTP packet flows belonging to a range of UDP destination ports.
map-class frame-relay	Specifies a map class to define QoS values for an SVC.
priority	Gives priority to a class within a policy map.
show frame-relay pvc	Displays statistics about PVCs for Frame Relay interfaces.
show queue	Displays the contents of packets inside a queue for a particular interface or VC.
show traffic-shape queue	Displays information about the elements queued at a particular time at the VC (DLCI) level.