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This feature module describes the FRF.12 Support on Switched Frame Relay PVCs feature. It includes information on the benefits of the new feature, supported platforms, related documents, and so on.
This document includes the following sections:
The FRF.12 Support on Switched Frame Relay PVCs feature brings existing end-to-end FRF.12 fragmentation functionality to switched Frame Relay permanent virtual circuits (PVCs).
The FRF.12 Implementation Agreement allows long data frames to be fragmented into smaller pieces. This process allows real-time traffic and non-real-time traffic to be carried together on lower-speed links without causing excessive delay to the real-time traffic.
Some Frame Relay access devices do not support the FRF.12 standard for end-to-end fragmentation. Large packets sourced from these devices can cause significant serialization delay across low-speed trunks in switched networks.
The FRF.12 Support on Switched Frame Relay PVCs feature helps prevent this delay by bringing end-to-end FRF.12 fragmentation to routers that are acting as switches on the edge of switched Frame Relay networks. An edge router that receives large packets from a Frame Relay access device will fragment those packets before transmitting them across the switched network. The edge router that receives the fragmented packets will reassemble those packets before sending them to a Frame Relay access device that does not support FRF.12. If the receiving Frame Relay access device does support FRF.12, the router will transmit the fragmented packets without reassembling them.
You can configure FRF.12 fragmentation on switched PVCs using the frame-relay fragment map-class command with the new switched keyword.
This new feature provides FRF.12 fragmentation support on switched Frame Relay PVCs. This functionality prevents delay in switched Frame Relay networks by allowing the routers on the edge of the network to fragment large data packets before transmitting them across the network.
If the Frame Relay access device does not support FRF.12 fragmentation, the FRF.12 Support on Switched Frame Relay PVCs feature will not benefit the interface between the Frame Relay access device and the edge router. Fragmentation and reassembly occur on the interface between the edge router and the switched Frame Relay network.
If the Frame Relay access device is sending voice and unfragmented data on the same PVC, voice quality will suffer. The edge router will not reorder packets on switched PVCs.
Standards
Frame Relay Fragmentation Implementation Agreement (FRF.12), Frame Relay Forum, December, 1997.
MIBs
No new or modified MIBs are supported by this feature.
For descriptions of supported MIBs and how to use MIBs, see the Cisco MIB web site on Cisco Connectin Online (CCO) at http://www.cisco.com/public/sw-center/netmgmt/cmtk/mibs.shtml.
RFCs
No new or modified RFCs are supported by this feature.
The following prerequisites apply to the FRF.12 Support on Switched Frame Relay PVCs feature:
See the following sections for configuration tasks for the FRF.12 Support on Switched Frame Relay PVCs feature. Each task in the list is identified as optional or required.
To configure FRF.12 on a switched PVC, use the following map-class configuration command:
| Command | Purpose |
|---|---|
Router(config-map-class)#frame-relay fragment fragment_size [switched] | Enables fragmentation of Frame Relay frames for a Frame Relay map class. |
To verify that FRF.12 fragmentation is configured and working correctly, use one or more of the following privileged EXEC commands:
| Command | Purpose |
|---|---|
Router#show frame-relay fragment [interface interface] [dlci] | Displays statistics about Frame Relay fragmentation. |
Router#show frame-relay pvc [interface interface] [dlci] | Displays statistics about PVCs for Frame Relay interfaces. |
This section provides a configuration example for the FRF.12 Support on Switched Frame Relay PVCs feature.
In the following example, FRF.12 fragmentation is configured in a map class called "data." The "data" map class is assigned to switched pvc 20 on serial interface 3/3.
frame-relay switching ! interface Serial3/2 encapsulation frame-relay frame-relay intf-type dce ! interface Serial3/3 encapsulation frame-relay frame-relay traffic-shaping frame-relay interface-dlci 20 switched class data frame-relay intf-type dce ! map-class frame-relay data frame-relay fragment 80 switched frame-relay cir 64000 frame-relay bc 640 ! connect data Serial3/2 16 Serial3/3 20
This section documents the new command that configures the FRF.12 Support on Switched Frame Relay PVCs feature.
To enable fragmentation of Frame Relay frames for a Frame Relay map class, use the frame-relay fragment map-class configuration command. To disable Frame Relay fragmentation, use the no form of this command.
frame-relay fragment fragment_size [switched]
Syntax Description
fragment_size Specifies the number of payload bytes from the original Frame Relay frame that will go into each fragment. This number excludes the Frame Relay header of the original frame. All the fragments of a Frame Relay frame except the last will have a payload size equal to fragment_size; the last fragment will have a payload size less than or equal to fragment_size. Valid values are from 16 to 1600 bytes; the default is 53. switched (Optional) Specifies that fragmentation will be enabled on a switched PVC.
Defaults
Disabled.
Command Modes
Map-class configuration
Command History
12.0(3)XG This command was introduced. 12.0(4)T This command was implemented in Cisco IOS Release 12.0 T. 12.1(2)T This command was modified to enable end-to-end FRF.12 fragmentation on switched PVCs.
Release
Modification
Usage Guidelines
Frame Relay fragmentation is enabled on a per-PVC basis. Before enabling Frame Relay fragmentation, you must first associate a Frame Relay map class with a specific data-link connection identifier (DLCI), and then enter map-class configuration mode and enable or disable fragmentation for that map class. In addition, you must enable Frame Relay traffic shaping on the interface in order for fragmentation to work.
Frame Relay frames are fragmented using one of the following formats, depending on how the PVC is configured:
Only pure end-to-end FRF.12 fragmentation can be configured on switched PVCs.
Cisco recommends pure end-to-end FRF.12 fragmentation on PVCs that are carrying Voice over IP (VoIP) packets and on PVCs that are sharing the link with other PVCs carrying Voice over Frame Relay (VoFR) traffic.
In pure end-to-end FRF.12 fragmentation, Frame Relay frames that have a payload less than the fragment size configured for that PVC are transmitted without the fragmentation header.
FRF.11 Annex C and Cisco proprietary fragmentation are used when VoFR frames are transmitted on a PVC. When fragmentation is enabled on a PVC, FRF.11 Annex C format is triggered when vofr is configured on that PVC; Cisco proprietary format is triggered when vofr cisco is configured.
In FRF.11 Annex C and Cisco proprietary fragmentation, VoFR frames are never fragmented, and all data packets (including VoIP packets) contain the fragmentation header, regardless of the payload size.
Examples
FRF.12 Fragmentation on a Switched PVC Example
The following example shows how to configure pure end-to-end FRF.12 fragmentation in the map class "data." The map class is associated with switched PVC 20 on serial interface 3/3.
router(config)#frame-relay switching !router(config)#interface Serial3/2 router(config-if)# encapsulation frame-relay router(config-if)# frame-relay intf-type dce !router(config)#interface Serial3/3 router(config-if)# encapsulation frame-relay router(config-if)# frame-relay traffic-shaping router(config-if)# frame-relay interface-dlci 20 switched router(config-fr-dlci)# class data router(config-if)# frame-relay intf-type dce !router(config)#map-class frame-relay data router(config-map-class)# frame-relay fragment 80 switched router(config-map-class)# frame-relay cir 64000 router(config-map-class)# frame-relay bc 640 !router(config)#connect data Serial3/2 16 Serial3/3 20
FRF.12 Fragmentation on a Terminated PVC Example
The following example shows how to enable pure end-to-end FRF.12 fragmentation for the "frag" map class on a Cisco 2600 series, 3600 series, or 7200 series router, starting from global configuration mode. The fragment payload size is set to 40 bytes. Frame Relay traffic shaping is required on the PVC; the only queueing type supported on the PVC when fragmentation is configured is weighted fair queueing (WFQ).
router(config)#interface serial 1/0/0 router(config-if)# frame-relay traffic-shaping router(config-if)# frame-relay interface-dlci 100 router(config-fr-dlci)# class frag router(config-fr-dlci)# exitrouter(config)#map-class frame-relay frag router(config-map-class)# frame-relay cir 128000 router(config-map-class)# frame-relay bc 1000 router(config-map-class)# frame-relay fragment 40 router(config-map-class)# frame-relay fair-queue router(config-map-class)#
FRF.11 Annex C Fragmentation Example
The following example shows how to enable FRF.11 Annex C fragmentation for data on a CiscoMC3810 PVC configured for VoFR. Note that fragmentation must be configured if a VoFR PVC is to carry data. The fragment payload size is set to 40 bytes. Frame Relay traffic shaping is required on the PVC; the only queueing type supported on the PVC when fragmentation is configured is weighted fair queueing (WFQ).
router(config)#interface serial 1/1 router(config-if)# frame-relay traffic-shaping router(config-if)# frame-relay interface-dlci 101 router(config-fr-dlci)# vofr router(config-fr-dlci)# class frag router(config-fr-dlci)# exitrouter(config)#map-class frame-relay frag router(config-map-class)# frame-relay cir 128000 router(config-map-class)# frame-relay bc 1000 router(config-map-class)# frame-relay fragment 40 router(config-map-class)# frame-relay fair-queue router(config-map-class)#
Cisco Proprietary Frame Relay Fragmentation Example
The following example shows how to enable Cisco proprietary Frame Relay fragmentation for the "frag" Frame Relay map class on a Cisco 2600 series, 3600 series, or 7200 series router, starting from global configuration mode. The fragment payload size is set to 40 bytes. Frame Relay traffic shaping is required on the PVC; the only queueing type supported on the PVC when fragmentation is configured is weighted fair queueing (WFQ).
router(config)#interface serial 2/0/0 router(config-if)# frame-relay traffic-shaping router(config-if)# frame-relay interface-dlci 102 router(config-fr-dlci)# vofr cisco router(config-fr-dlci)# class frag router(config-fr-dlci)# exitrouter(config)#map-class frame-relay frag router(config-map-class)# frame-relay cir 128000 router(config-map-class)# frame-relay bc 1000 router(config-map-class)# frame-relay fragment 40 router(config-map-class)# frame-relay fair-queue router(config-map-class)#
Related Commands
class (virtual circuit) Associates a map class with a specified DLCI. frame-relay fair-queue Enables weighted fair queueing for one or more Frame Relay PVCs. frame-relay interface-dlci Assigns a DLCI to a specified Frame Relay subinterface on the router or access server. frame-relay traffic-shaping Enables traffic shaping and per-virtual circuit queueing for all PVCs and SVCs1 on a Frame Relay interface. map-class frame-relay Specifies a map class to define QoS2 values for an SVC.
Command
Description
Posted: Tue Jun 27 14:40:40 PDT 2000
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