Distributed Link Fragmentation and Interleaving over Leased Lines

Table Of Contents

Distributed Link Fragmentation and Interleaving over Leased Lines

Contents

Prerequisites for Distributed Link Fragmentation and Interleaving over Leased Lines

Cisco 7500 Series Routers Prerequisites

Cisco 7600 Series Router Prerequisites

Restrictions for Distributed Link Fragmentation and Interleaving over Leased Lines

Information About Distributed Link Fragmentation and Interleaving over Leased Lines

Overview of Distributed Link Fragmentation and Interleaving (dLFI)

Benefits

Related Features and Technologies

Supported Platforms

Configuration Tasks

Configuring LFI Using MLP over Frame Relay

Configuring Distributed Low Latency Queueing and Other QoS Features in a Traffic Policy

Configuring LFI Using MLP on a Virtual Template Interface

Associating the Virtual Template Interface with a Frame Relay PVC

Configuring LFI Using MLP over ATM

Configuring Distributed Low Latency Queueing and Other QoS Features in a Traffic Policy

Configuring LFI Using MLP in a Virtual Template Interface

Associating the Virtual Template Interface with an ATM PVC

Configuring LFI Using MLP over a Leased Line

Configuring Distributed Low Latency Queueing and Other QoS Features in a Traffic Policy

Configuring the Channel Group

Creating a Multilink Group

Assigning an Interface to a Multilink Group

Verifying LFI for Frame Relay, ATM, or Leased Lines

Monitoring and Maintaining LFI for Frame Relay, ATM, or Leased Lines

Configuration Examples

LFI over Frame Relay Configuration Example

LFI over ATM Configuration Example

LFI over Leased Line Configuration Example

Monitoring LFI Example

Additional References

Related Documents

Standards

MIBs

RFCs

Technical Assistance

Command Reference

ppp multilink interleave

Glossary

Distributed Link Fragmentation and Interleaving over Leased Lines

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The Distributed Link Fragmentation and Interleaving over Leased Lines feature extends distributed link fragmentation and interleaving functionality to leased lines. It supports the transport of voice traffic and data traffic on lower-speed Frame Relay and ATM virtual circuits (VCs) and on leased lines without causing excessive delay to the real-time voice traffic.

Feature History for Distributed Link Fragmentation and Interleaving over Leased Lines

Cisco IOS Release	Modification
12.2(4)T3	The Distributed Link Fragmentation and Interleaving feature was introduced. This version of the feature supported Distributed Link Fragmentation and Interleaving for ATM and Frame Relay.
12.2(8)T	The Distributed Link Fragmentation and Interleaving over Leased Lines feature was introduced. This feature introduced Distributed Link Fragmentation and Interleaving on leased lines.
12.0(24)S	The Distributed Link Fragmentation and Interleaving over Leased Lines feature was introduced on Cisco IOS Release 12.0 S. This feature introduced Distributed Link Fragmentation and Interleaving on leased lines. Distributed Link Fragmentation and Interleaving is not available for ATM and Frame Relay using Cisco IOS Release 12.0 S.
12.2(14)SX	The Distributed Link Fragmentation and Interleaving feature was introduced on the Catalyst 6500 series switch and Cisco 7600 series router FlexWAN module.
12.2(27)SBA	The Distributed Link Fragmentation and Interleaving over Leased Lines feature was integrated into Cisco IOS Release 12.2(27)SBA for the Cisco 7500 series router. This feature is not available on ATM and Frame Relay in Cisco IOS Release 12.2(27)SBA.

Finding Support Information for Platforms and Cisco IOS Software Images

Use Cisco Feature Navigator to find information about platform support and Cisco IOS software image support. Access Cisco Feature Navigator at http://www.cisco.com/go/fn. You must have an account on Cisco.com. If you do not have an account or have forgotten your username or password, click Cancel at the login dialog box and follow the instructions that appear.

Contents

•Prerequisites for Distributed Link Fragmentation and Interleaving over Leased Lines

•Restrictions for Distributed Link Fragmentation and Interleaving over Leased Lines

•Information About Distributed Link Fragmentation and Interleaving over Leased Lines

•Configuration Tasks

•Monitoring and Maintaining LFI for Frame Relay, ATM, or Leased Lines

•Configuration Examples

•Additional References

•Command Reference

•Glossary

Prerequisites for Distributed Link Fragmentation and Interleaving over Leased Lines

The following prerequisites apply for support of dLFI on the Cisco 7500 series routers and on the Cisco 7600 series routers and Catalyst 6500 series switches with a FlexWAN:

•Cisco 7500 Series Routers Prerequisites

•Cisco 7600 Series Router Prerequisites

Cisco 7500 Series Routers Prerequisites

•The minimum required VIP for dLFI is a VIP2-50. A VIP2-50 with a minimum of 64 MB DRAM and 4 MB SRAM or a VIP4-80 with a minimum of 128 MB SDRAM as program memory and 64 MB SDRAM as packet memory is required to run dLFI. The VIP4-80 will provide better performance in most networking environments.

The amount of required DRAM and SRAM is proportional to the number of PVCs and interfaces; therefore, additional DRAM and SRAM might be necessary if additional PVCs or interfaces are added and VIP CPU is available. If VIP CPU has reached its maximum threshold, additional DRAM and SRAM will not be useful for adding additional PVCs or interfaces.

•RSP2 with a minimum of 64 MB of DRAM

•Distributed Low Latency Queueing (dLLQ). The interleaving of packets occurs only when a QoS traffic policy that contains a dLLQ configuration is attached to a PVC or an interface. If dLLQ is not configured on the PVC or interface, packets will be fragmented but not interleaved.

The priority policy map class command is used to configure dLLQ in a QoS traffic policy, and the service-policy interface command is used to attach the QoS traffic policy to an interface or a PVC.

•Distributed Cisco Express Forwarding (dCEF) must be globally enabled. You can enable dCEF using the ip cef distributed command in global configuration mode.

•A virtual template or a multilink interface must be shutdown and then re-enabled (using the shutdown command followed by the no shutdown command) to change any PPP configuration. The exception to this restriction is the QoS traffic policy, which does not require the shutdown/no shutdown sequence in order to be enabled.

•All currently available serial port adapters for the Cisco 7500 series routers support dLFI using MLP over Frame Relay. These port adapters include:

–PA-4T+

–PA-8T

–PA-MC-T3

–PA-CE3

–PA-MC-2E1/120

–PA-MC-2T1

–PA-MC-2T3+

–PA-MC-4T1

–PA-MC-8DSX1

–PA-MC-8E1/120

–PA-MC-8T1

–PA-MC-E3

•All currently available channelized serial port adapters for Cisco 7500 series routers support dLFI over leased lines. These port adapters include:

–PA-MC-2E1/120

–PA-MC-2T1

–PA-MC-2T3+

–PA-MC-4T1

–PA-MC-8DSX1

–PA-MC-8E1/120

–PA-MC-8T1

–PA-MC-E3

–PA-MC-STM1

•MLP over ATM must use a PA-A3 ATM port adapter. Therefore, only PA-A3 ATM port adapters support dLFI using MLP over ATM.

–PA-A3-E3

–PA-A3-OC3

–PA-A3-T3

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Note The PA-A3 IMA port adapter is not supported by dLFI.

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Cisco 7600 Series Router Prerequisites

The following prerequisites apply to dLFI support on the Cisco 7600 series routers and Catalyst 6500 series switches with a FlexWAN:

•Distributed Low Latency Queueing (dLLQ). The interleaving of packets occurs only when a QoS traffic policy that contains a dLLQ configuration is attached to a PVC or an interface. If dLLQ is not configured on the PVC or interface, packets will be fragmented but not interleaved.

The priority policy map class command is used to configure dLLQ in a QoS traffic policy, and the service-policy interface command is used to attach the QoS traffic policy to an interface or a PVC.

•A virtual template or a multilink interface must be shutdown and then re-enabled (using the shutdown command followed by the no shutdown command) to change any PPP configuration. The exception to this restriction is the QoS traffic policy, which does not require the shutdown/no shutdown sequence in order to be enabled.

•All currently available serial port adapters for the FlexWAN support LFI using MLP over Frame Relay:

–PA-4T+

–PA-8T

–PA-MC-T3

–PA-MC-2T3+

–PA-MC-4T1

–PA-MC-8E1/120

–PA-MC-8T1

–PA-MC-E3

•All currently available channelized serial port adapters for the FlexWAN support LFI over leased lines:

–PA-MC-2T3+

–PA-MC-4T1

–PA-MC-8E1/120

–PA-MC-8T1

–PA-MC-E3

–PA-MC-STM1

•MLP over ATM must use a PA-A3 ATM port adapter. The following PA-A3 ATM port adapters support LFI using MLP over ATM:

–PA-A3-E3

–PA-A3-OC3

–PA-A3-T3

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Note The PA-A3 IMA port adapter is not supported by dLFI.

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Restrictions for Distributed Link Fragmentation and Interleaving over Leased Lines

The following restrictions apply to the Distributed Link Fragmentation and Interleaving feature:

•Many of the older queueing mechanisms are not supported by dLFI. These mechanisms include:

–Fair-queueing on a virtual template interface

–Random-detect on a virtual template interface

–Custom queueing

–Priority queueing

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Note Fair queueing, random detection (dWRED), and priority queueing can be configured in a traffic policy using the Modular QoS CLI.

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•Compressed Real-Time Transport Protocol (CRTP) configurations should not be configured on the multilink interface when the following feature combination is configured:

–Link Fragmentation and Interleaving (LFI) is enabled on the multilink interface

–The multilink bundle has more than one member link

–QoS policy with a priority feature is enabled on the multilink interface

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Note In a dMLP/dLFI configuration, priority packets do not carry MLP header and sequence number. Thus, MLP distributes the priority packets across all member links. As a result, packets that are compressed by CRTP may arrive out-of-order at the receiving router. This prohibits CRTP from decompressing the packet header and forces CRTP to drop the packets.

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•Only one link per MLP bundle is supported when using dLFI over Frame Relay or dLFI over ATM. If more than one link is used in an MLP bundle when using dLFI over Frame Relay or dLFI over ATM, dLFI is automatically disabled. When using dLFI over leased lines, more than one link can be configured with dLFI in the MLP bundle.

QoS traffic policies will function properly in MLP bundles with more than one link, however.

•Only Voice over IP is supported; Voice over Frame Relay and Voice over ATM are not supported by the dLFI feature.

Information About Distributed Link Fragmentation and Interleaving over Leased Lines

This section describes the concepts and information that the user should understand about this feature. The following concepts and information are described in this section:

•Overview of Distributed Link Fragmentation and Interleaving (dLFI)

•Benefits

•Related Features and Technologies

•Supported Platforms

Overview of Distributed Link Fragmentation and Interleaving (dLFI)

The Distributed Link Fragmentation and Interleaving over Leased Lines feature extends distributed link fragmentation and interleaving functionality to leased lines. Previously, Distributed Link Fragmentation and Interleaving was only available for Frame Relay and ATM on Cisco IOS Release 12.2 T. Distributed Link Fragmentation and Interleaving is not available for Frame Relay and ATM using Cisco IOS Release 12.0 S.

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Note Distributed Link Fragmentation and Interleaving for Frame Relay, ATM, and Leased Lines is often referred to as dLFI in this document. This document covers the procedures for configuring dLFI on Frame Relay and ATM in addition to covering the procedure for configuring dLFI on a leased line.

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The dLFI feature supports the transport of real-time traffic, such as voice, and non-real-time traffic, such as data, on lower-speed Frame Relay and ATM virtual circuits (VCs) and on leased lines without causing excessive delay to the real-time traffic.

This feature is implemented using multilink PPP (MLP) over Frame Relay, ATM, and leased lines. The feature enables delay-sensitive real-time packets and non-real-time packets to share the same link by fragmenting the large data packets into a sequence of smaller data packets (fragments). The fragments are then interleaved with the real-time packets. On the receiving side of the link, the fragments are reassembled and the packet reconstructed.

The dLFI feature is often useful in networks that send real-time traffic using Distributed Low Latency Queueing, such as voice, but have bandwidth problems that delay this real-time traffic due to the transport of large, less time-sensitive data packets. The dLFI feature can be used in these networks to disassemble the large data packets into multiple segments. The real-time traffic packets then can be sent between these segments of the data packets. In this scenario, the real-time traffic does not experience a lengthy delay waiting for the low-priority data packets to traverse the network. The data packets are reassembled at the receiving side of the link, so the data is delivered intact.

The ability to configure Quality of Service (QoS) using the Modular QoS CLI while also using distributed MLP (dMLP) is also introduced as part of the dLFI feature. The ability to configure QoS using the Modular QoS CLI while using dMLP was not supported prior to the introduction of the dLFI feature.

The following figure illustrates how dLFI fragments a larger data packet to allow time-sensitive traffic, in this case voice traffic, to be delivered in a more timely manner.

Figure 1 Distributed Link Fragmentation and Interleaving Example

Benefits

End-to-End Voice over IP Quality

This new feature enhances Voice over IP (VoIP) Quality of Service (QoS) by preventing delay, delay variation (jitter), and packet loss for voice traffic on low speed ATM-to-ATM and ATM-to-Frame Relay networks and on leased lines.

Interoperability with Other QoS Features

The dLFI feature works concurrently with and on the same switching path as other QoS features, ensuring high quality and scalable VoIP deployment.

The dLFI feature works in conjunction with most of the following QoS features:

•Distributed Low Latency Queueing (dLLQ, the priority command)

•Distributed Traffic Shaping (dTS, the shape command)

•Distributed Compressed Real-Time Transport Protocol (dCRTP, the ip [rtp | tcp] connections and other compression commands)

•Distributed Class-Based Weighted Fair Queueing (dCBWFQ, the bandwidth, fair-queue, and queue-limit commands)

•Distributed Weighted Random Early Detection (dWRED, the random-detect command)

•Class-Based Marking (the set command)

•Traffic Policing (the police command)

Increased Call Support for Voice on VIP-Enabled Cisco 7500 Series Routers

The dLFI feature enhances the scalability on interfaces and Permanent Virtual Circuits (PVCs), thereby allowing support for additional calls on VIP-enabled Cisco 7500 series routers.

Related Features and Technologies

•Frame Relay/ATM interworking (FRF.8)

•Distributed Frame Relay fragmentation (FRF.12)

•Distributed Multilink Point-to-Point Protocol (dMLP)

•The dLFI feature works in conjunction with most Quality of Service (QoS) features, including the QoS features listed below:

–Distributed Low Latency Queueing (dLLQ, the priority command)

–Distributed Traffic Shaping (dTS, the shape command)

–Distributed Compressed Real-Time Transport Protocol (dCRTP, the ip [rtp | tcp] connections and other compression commands)

–Distributed Class-Based Weighted Fair Queueing (dCBWFQ, the bandwidth, fair-queue, and queue-limit commands)

–Class-Based Marking (the set command)

–Traffic Policing (the police command)

Supported Platforms

•Cisco 7600 series routers and Catalyst 6500 series switches with a FlexWAN

•Cisco 7500 series routers with a VIP2-50 or higher

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Note A VIP2-50 with a minimum of 64 MB DRAM and 4 MB SRAM or a VIP4-80 with a minimum of 128 MB SDRAM as program memory and 64 MB SDRAM as packet memory are required to run dLFI on the Cisco 7500 series routers. The VIP4-80 will provide better performance in most networking environments.

The "Prerequisites for Distributed Link Fragmentation and Interleaving over Leased Lines" section of this document details other requirements, including port adapter requirements.

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Configuration Tasks

See the following sections for configuration tasks for the dLFI feature. Each task in the list is identified as optional or required.

•Configuring LFI Using MLP over Frame Relay (required for configuring dLFI on Frame Relay. Not available on Cisco IOS Release 12.0 S)

•Configuring LFI Using MLP over ATM (required for configuring dLFI on ATM. Not available on Cisco IOS Release 12.0 S)

•Configuring LFI Using MLP over a Leased Line (required for configuring dLFI on a leased lines)

•Verifying LFI for Frame Relay, ATM, or Leased Lines (optional)

Configuring LFI Using MLP over Frame Relay

To configure LFI using MLP over Frame Relay, perform the tasks in the following sections:

•Configuring Distributed Low Latency Queueing and Other QoS Features in a Traffic Policy

•Configuring LFI Using MLP on a Virtual Template Interface

•Associating the Virtual Template Interface with a Frame Relay PVC

Configuring Distributed Low Latency Queueing and Other QoS Features in a Traffic Policy

The dLLQ feature must be enabled in order for the dLFI feature to interleave packet fragments. The dLLQ feature is configured in a QoS traffic policy, which is attached to the multilink group. Other QoS features can also be configured in the traffic policy.

A traffic policy using dLLQ and other QoS features can be configured by entering the following commands:

	Command	Purpose
Step 1	Router(config)# class-map [match-any | match-all] class-map-name	Specifies the user-defined name of the traffic class and enters class map configuration mode. A traffic class is used to classify traffic.
Step 2	Router(config-cmap)# match match-criterion	Specifies the criteria to classify traffic against. If traffic matches the specified match criteria, traffic is said to belong to the traffic class. Multiple match criterion can be specified in a single traffic class.
Step 3	Router(config-cmap)# exit	Exits class map configuration mode.
Step 4	Router(config)# policy-map policy-name	Specifies the name of the QoS traffic policy to configure and enters policy map configuration mode.
Step 5	Router(config-pmap)# class class-map-name	Specifies the name of a predefined class included in the service policy. This traffic class classifies traffic; the QoS features configured in the traffic policy determine how to forward traffic that matches the traffic class configuration. In these instructions, the class-map-name option should match the class-map-name entered in Step 1 of this procedure.
Step 6	Router(config-pmap-c)# priority [percent] [kpbs | percent] [bytes]	Reserves a priority queue with a specified amount or percent of available bandwidth for high-priority traffic. The priority command is used to enable dLLQ.
Step 7	Router(config-pmap-c)#	Enables a QoS feature in the traffic policy.

Configuring LFI Using MLP on a Virtual Template Interface

To configure LFI using MLP on a virtual template interface, use the following interface configuration commands:

	Command	Purpose
Step 1	Router(config)# interface virtual-template number	Creates a virtual template and enters interface configuration mode.
Step 2	Router(config-if)# bandwidth kilobits	Sets the bandwidth value for an interface. The bandwidth value for the interface should match the traffic speed of the PVC; for instance, if the VBR peak cell rate is 128 kpbs, the kilobits option in the bandwidth command should be entered as 128. Similarly, if the PVC is being shaped to 64 kpbs, the kilobits option should be entered as 64.
Step 3	Router(config-if)# ip address ip-address mask	Sets a primary IP address for an interface.
Step 4	Router(config-if)# service-policy output policy-name	(Required for traffic leaving the virtual template interface) Attaches a previously configured QoS traffic policy, which contains QoS classification and configuration parameters, that evaluates and applies QoS features for traffic leaving the interface with the virtual template. The priority command must be configured in this traffic policy for dLFI to operate properly. In this example, the policy-name option should match the policy-name option given in Step 4 of the Configuring Distributed Low Latency Queueing and Other QoS Features in a Traffic Policy procedure. Note For dLFI, the QoS traffic policy that is attached using the service-policy command is attached to the virtual template. The QoS traffic policy does not have to be attached to the Frame Relay map class.
Step 5	Router(config-if)# service-policy input policy-name	(Required for traffic entering the virtual template interface) Attaches a previously configured QoS traffic policy, which contains QoS classification and configuration parameters, that evaluates and applies QoS features, including dLLQ, for traffic entering the interface with the virtual template. The priority command must be configured in this traffic policy for dLFI to operate properly. In this example, the policy-name option should match the policy-name option given in Step 4 of the Configuring Distributed Low Latency Queueing and Other QoS Features in a Traffic Policy procedure. Note For dLFI, the QoS traffic policy that is attached using the service-policy command is attached on the virtual template. The QoS traffic policy does not have to be attached to the Frame Relay map class.
Step 6	Router(config-if)# ppp multilink	Enables MLP on the interface.
Step 7	Router(config-if)# ppp multilink fragment-delay milliseconds	Configures the maximum delay allowed for transmission of a packet fragment on an MLP bundle.
Step 8	Router(config-if)# ppp multilink interleave	Enables interleaving of packets among the fragments of larger packets on an MLP bundle.

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Note Fragment size at the MLP bundle can be configured using the following formula:
fragment size = bandwidth x fragment-delay / 8

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Associating the Virtual Template Interface with a Frame Relay PVC

To associate the virtual template interface with a Frame Relay PVC, use the following commands beginning in global configuration mode:

	Command	Purpose
Step 1	Router(config)# interface type number	Configures an interface type and enters interface configuration mode.
Step 2	Router(config-if)# frame-relay interface-dlci dlci [ppp virtual-template-name]	Associates a virtual template interface with a Frame Relay DLCI.1

1 DLCI = data-link connection identifier

Configuring LFI Using MLP over ATM

LFI using MLP can be configured over ATM using a virtual template interface. To configure LFI using MLP over ATM using a virtual template interface, perform the tasks in the following sections:

•Configuring Distributed Low Latency Queueing and Other QoS Features in a Traffic Policy

•Configuring LFI Using MLP in a Virtual Template Interface

•Associating the Virtual Template Interface with an ATM PVC

Configuring Distributed Low Latency Queueing and Other QoS Features in a Traffic Policy

The dLLQ feature must be enabled in order for the dLFI feature to interleave packet fragments. The dLLQ feature is configured in a QoS traffic policy, which is attached to the multilink group. Other QoS features can also be configured in the traffic policy.

A traffic policy using dLLQ and other QoS features can be configured by entering the following commands:

	Command	Purpose
Step 1	Router(config)# class-map [match-any | match-all] class-map-name	Specifies the user-defined name of the traffic class and enters class map configuration mode. A traffic class is used to classify traffic.
Step 2	Router(config-cmap)# match match-criterion	Specifies the criteria to classify traffic against. If traffic matches the specified match criteria, traffic is said to belong to the traffic class. Multiple match criterion can be specified in a single traffic class.
Step 3	Router(config-cmap)# exit	Exits class map configuration mode.
Step 4	Router(config)# policy-map policy-name	Specifies the name of the QoS traffic policy to configure and enters policy map configuration mode.
Step 5	Router(config-pmap)# class class-map-name	Specifies the name of a predefined class included in the service policy. This traffic class classifies traffic; the QoS features configured in the traffic policy determine how to forward traffic that matches the traffic class configuration. In these instructions, the class-map-name option should match the class-map-name entered in Step 1 of this procedure.
Step 6	Router(config-pmap-c)# priority [percent] [kpbs | percent] [bytes]	Reserves a priority queue with a specified amount or percentage of available bandwidth for high-priority traffic. The priority command is used to enable dLLQ.
Step 7	Router(config-pmap-c)#	Enables a QoS feature in the traffic policy.

Configuring LFI Using MLP in a Virtual Template Interface

To configure dLFI using MLP on a virtual template interface, use the following interface configuration commands:

	Command	Purpose
Step 1	Router(config)# interface virtual-template number	Creates a virtual template and enters interface configuration mode.
Step 2	Router(config-if)# bandwidth kilobits	Sets the bandwidth value for an interface.
Step 3	Router(config-if)# ip address ip-address mask	Sets a primary IP address for an interface.
Step 4	Router(config-if)# service-policy output policy-name	(Required for traffic leaving the virtual template interface) Attaches a previously configured QoS traffic policy, which contains QoS classification and configuration parameters, that evaluates and applies QoS features, including dLLQ, for traffic leaving the interface with the virtual template. The priority command must be configured in this traffic policy for dLFI to operate properly. In this example, the policy-name option should match the policy-name option given in Step 4 of the Configuring Distributed Low Latency Queueing and Other QoS Features in a Traffic Policy procedure. Note For dLFI, the QoS traffic policy that is attached using the service-policy command is attached to the virtual template. The QoS traffic policy does not have to be attached to the ATM PVC.
Step 5	Router(config-if)# service-policy input policy-name	(Required for traffic entering the virtual template interface) Attaches a previously configured QoS traffic policy, which contains QoS classification and configuration parameters, that evaluates and applies QoS features, including dLLQ, for traffic entering the interface with the virtual template. The priority command must be configured in this traffic policy for dLFI to operate properly. In this example, the policy-name option should match the policy-name option given in Step 4 of the Configuring Distributed Low Latency Queueing and Other QoS Features in a Traffic Policy procedure. Note For dLFI, the QoS traffic policy that is attached using the service-policy command is attached to the virtual template. The QoS traffic policy does not have to be attached to the ATM PVC.
Step 6	Router(config-if)# ppp multilink	Enables MLP on the interface.
Step 7	Router(config-if)# ppp multilink fragment-delay milliseconds	Configures the maximum delay allowed for transmission of a packet fragment on an MLP bundle.
Step 8	Router(config-if)# ppp multilink interleave	Enables interleaving of packets among the fragments of larger packets on an MLP bundle.

Fragment size at the MLP bundle can be configured using the following formula:

fragment size = bandwidth x fragment-delay / 8

The ideal fragment size for MLP over ATM should allow the fragments to fit into an exact multiple of ATM cells. The fragment size for MLP over ATM can be calculated using the following formula:

fragment size = 48 x number of cells - 10

Associating the Virtual Template Interface with an ATM PVC

To associate the virtual template interface with an ATM PVC, use the following commands beginning in global configuration mode:

	Command	Purpose
Step 1	Router(config)# interface atm slot/0 or Router(config)# interface atm slot/port	Specifies the ATM interface type and enters interface configuration mode.1
Step 2	Router(config-if)# pvc [name] vpi/vci	Creates an ATM PVC.
Step 3	Router(config-if-atm-vc)# abr output-pcr output-mcr	Selects ABR2 QoS and configures the output peak cell rate and output minimum guaranteed cell rate for an ATM PVC.
Step 4	Router(config-if-atm-vc)# protocol ppp virtual-template number	Specifies that PPP is established over the ATM PVC using the configuration from the specified virtual template.

1 To determine the correct form of the interface atm command, consult your ATM network module, port adapter, or router documentation. 2 ABR = available bit rate

Configuring LFI Using MLP over a Leased Line

LFI over a leased line can be configured using MLP. To configure LFI over a leased line, perform the tasks in the following sections:

•Configuring Distributed Low Latency Queueing and Other QoS Features in a Traffic Policy

•Assigning an Interface to a Multilink Group

•Configuring the Channel Group

•Creating a Multilink Group

•Assigning an Interface to a Multilink Group

Configuring Distributed Low Latency Queueing and Other QoS Features in a Traffic Policy

The dLLQ feature must be enabled in order for the dLFI feature to interleave packet fragments. The dLLQ feature is configured in a QoS traffic policy which is attached to the multilink group. Other QoS features can also be configured in the traffic policy.

A traffic policy using dLLQ and other QoS features can be configured by entering the following commands:

	Command	Purpose
Step 1	Router(config)# class-map [match-any | match-all] class-map-name	Specifies the user-defined name of the traffic class and enters class map configuration mode. A traffic class is used to classify traffic.
Step 2	Router(config-cmap)# match match-criterion	Specifies the criteria to classify traffic against. If traffic matches the specified match criteria, traffic is said to belong to the traffic class. Multiple match criterion can be specified in a single traffic class.
Step 3	Router(config-cmap)# exit	Exits class map configuration mode.
Step 4	Router(config)# policy-map policy-name	Specifies the name of the QoS traffic policy to configure and enters policy map configuration mode.
Step 5	Router(config-pmap)# class class-map-name	Specifies the name of a predefined class included in the service policy. This traffic class classifies traffic; the QoS features configured in the traffic policy determine how to forward traffic that matches the traffic class configuration. In these instructions, the class-map-name option should match the class-map-name entered in Step 1 of this procedure.
Step 6	Router(config-pmap-c)# priority [percent] [kpbs | percent] [bytes]	Reserves a priority queue with a specified amount or percentage of available bandwidth for high-priority traffic. The priority command is used to enable dLLQ.
Step 7	Router(config-pmap-c)#	Enables a QoS feature in the traffic policy.

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Note The bandwidth command can be used in a QoS traffic policy to specify an amount of bandwidth to be reserved for the traffic policy. If the bandwidth command is used in a traffic policy that will be attached to a multilink interface, the following guidelines should be followed:
1. Use bandwidth percent in favor of bandwidth kpbs if possible. If the bandwidth kpbs option is specified as member links join and leave the bundle, the bandwidth setting will not adjust to the new aggregate bandwidth and the QoS traffic policy will either consume more bandwidth than desired or not have enough available bandwidth. Because the bandwidth percent option adjusts accordingly when new members links are added or removed, the amount of available bandwidth is properly adjusted when new member links are added or removed.
2. If bandwidth kpbs must be used, specify a bandwidth statement for the multilink group to reflect the expected available bandwidth for the multilink group. This bandwidth should be identical to the amount of bandwidth specified in the channel configuration when the channel-group command is entered (See Step 2 in the "Configuring the Channel Group" section of this document). For instance, if two channels are defined using the DS0 rate (64 kpbs), the kilobits variable should be entered as 128.

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Configuring the Channel Group

A channel group is used to configure the controllers. To configure the controller, enter the following commands:

	Command	Purpose
Step 1	Router(config)# controller [t1 | e1] slot/port	Configures a T1 or E1 controller.
Step 2	Router(config-controller)# channel-group channel-number timeslots range [speed {48 | 56 | 64}]	Defines the time slots that belong to each T1 or E1 circuit.

Creating a Multilink Group

To create a multilink group, use the following commands beginning in interface configuration mode:

	Command	Purpose
Step 1	Router(config)# interface multilink group-number	Creates and names a multilink bundle. The name of the multilink bundle is the group-number.
Step 2	Router(config-if)# ip address ip-address mask	Assigns an IP address for the multilink group.
Step 3	Router(config-if)# bandwidth kilobits	(Optional, unless a QoS traffic policy using the bandwidth kpbs command will be attached to the multilink group) Sets the bandwidth value for an interface. The bandwidth should match the parameters defined in channel configuration. For instance, if two channels are defined using the DS0 rate (64 kpbs), the kilobits variable should be entered as 128.
Step 4	Router(config-if)# ppp multilink	Enables MLP for the multilink group.
Step 5	Router(config-if)# ppp multilink fragment-delay milliseconds	Configures the maximum delay allowed for transmission of a packet fragment on an MLP bundle.
Step 6	Router(config-if)# ppp multilink interleave	Enables interleaving of packets among the fragments of larger packets on an MLP bundle.
Step 7	Router(config-if)# service-policy output policy-name	(Required for traffic leaving the multilink group) Attaches a previously configured QoS traffic policy, which contains QoS classification and configuration parameters, that evaluates and applies QoS features, including dLLQ, for traffic leaving the interface bundle. The priority command must be configured in this traffic policy for dLFI to operate properly. In this example, the policy-name option should match the policy-name option given in Step 4 of the Configuring Distributed Low Latency Queueing and Other QoS Features in a Traffic Policy procedure. Note For dLFI, the QoS traffic policy that is attached using the service-policy command is entered in the multilink group. The QoS traffic policy does not have to be attached to the serial interface that is part of the group.
Step 8	Router(config-if)# service-policy input policy-name	(Required for traffic entering the multilink group) Attaches a previously configured QoS traffic policy, which contains QoS classification and configuration parameters, that evaluates and applies QoS features, including dLLQ, for traffic entering the interface bundle. The priority command must be configured in this traffic policy for dLFI to operate properly. In this example, the policy-name option should match the policy-name option given in Step 4 of the Configuring Distributed Low Latency Queueing and Other QoS Features in a Traffic Policy procedure. Note For dLFI, the QoS traffic policy that is attached using the service-policy command is entered in the multilink group. The QoS traffic policy does not have to be attached to the serial interface that is part of the group.

Assigning an Interface to a Multilink Group

To configure an interface and attach the interface to a multilink group, use the following commands beginning in interface configuration mode:

	Command	Purpose
Step 1	Router(config)# interface serial interface-number	Specifies the serial interface to configure. Only serial interfaces can be bundled using multilink groups.
Step 2	Router(config-if)# no ip address	Removes any specified IP address.
Step 3	Router(config-if)# keepalive [seconds]	Sets the keepalive interval for the interface. The keepalive interval, which is the frequency at which the Cisco IOS software sends messages to itself or to the other end, is used to ensure a network interface is up. The seconds variable determines how often these messages are sent; for instance, if keepalive 5 is entered, a keepalive message is sent every 5 seconds.
Step 4	Router(config-if)# ppp chap hostname hostname	Specifies the hostname for the interface when Challenge Handshake Authentication Protocol (CHAP) is used for authentication. The CHAP hostname must be configured in order to avoid potential errors when more than one multilink group exists between the same two routers. A different hostname should be specified for each multilink group on a router.
Step 5	Router(config-if)# ppp multilink	Enables multilink PPP for the interface.
Step 6	Router(config-if)# multilink-group group-number	Assigns the interface to a multilink group. To assign the interface to a previously configured multilink group, the group-number variable in this step must match the group-number variable specified in the multilink group (in the "Creating a Multilink Group" section of this document, the group-number for the multilink group is specified in Step 1).

Verifying LFI for Frame Relay, ATM, or Leased Lines

To display information about LFI for Frame Relay, ATM, or leased lines using MLP, use the following privileged EXEC commands:

Command	Purpose
Router# show frame-relay pvc dlci	Displays statistics about PVCs for Frame Relay interfaces.
Router# show interfaces	Displays interleaving statistics. Interleaving data is displayed only if interleaving occurs.
Router# show ppp multilink	Displays bundle information for the MLP bundles and their PPP links in the router.
Router# show policy-map interface	Displays configurations and statistics of all input and output traffic policies attached to an interface.

Monitoring and Maintaining LFI for Frame Relay, ATM, or Leased Lines

To monitor LFI for Frame Relay, ATM, or leased lines using MLP, use the following privileged EXEC commands:

Command	Purpose
Router# show ppp multilink	Displays bundle information for the MLP bundles and their PPP links in the router. Displays dLFI statistics, including the number of fragmented, unfragmented, and reassembled packets, reassembly and fragmentation drops, and fragments that arrived out of sequence.
Router# debug ppp multilink fragments	Displays information about individual multilink fragments and important multilink events.
Router# debug voice RTP	Displays information about the interleaving of voice and data packets.

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Note The debug ppp multilink fragments and debug voice RTP commands have memory overhead and should not be used when memory is scarce or when traffic is very high.

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Configuration Examples

This section provides the following configuration examples:

•LFI over Frame Relay Configuration Example

•LFI over ATM Configuration Example

•LFI over Leased Line Configuration Example

•Monitoring LFI Example

LFI over Frame Relay Configuration Example

The following example shows the configuration of LFI using MLP over Frame Relay using a virtual template interface:

class-map voip

  match ip precedence 5

class-map business

  match ip precedence 3

policy-map llq-policy

  class voip

    priority 32

  class business

    bandwidth 32

policy-map shape-llq-policy

  class class-default

    shape average 80000 320 320

    service-policy llq-policy

policy-map input-policy

  class voip

    police 32000 1500 1500 conform-action transmit exceed-action drop

controller T1 5/1/0

  framing esf

  linecode b8zs

  channel-group 0 timeslots 1-2

interface Serial5/1/0:0

  no ip address

  encapsulation frame-relay

interface Serial5/1/0:0.1 point-to-point

  frame-relay interface-dlci 20 ppp Virtual-Template2

interface Virtual-Template2

  bandwidth 78

  ip address 98.0.0.2 255.0.0.0

  no keepalive

  service-policy output llq-policy

  service-policy input input-policy

  ppp multilink

  ppp multilink fragment-delay 8

  ppp multilink interleave

LFI over ATM Configuration Example

The following example shows the configuration of LFI using MLP on an ATM interface. This configuration uses a virtual template interface.

class-map voip

  match ip precedence 5

class-map business

  match ip precedence 3

policy-map llq-policy

  class voip

    priority 32

  class business

    bandwidth 32

policy-map input-policy

  class voip

    police 32000 1500 1500 conform-action transmit exceed-action drop

interface ATM4/0/0

  no ip address

  no atm ilmi-keepalive

interface ATM4/0/0.1 point-to-point

  pvc 0/34 

  abr 100 80

  protocol ppp Virtual-Template4

interface Virtual-Template4

  bandwidth 78

  ip address 88.0.0.2 255.0.0.0

  service-policy output llq-policy

  service-policy input input-policy

  ppp multilink

  ppp multilink fragment-delay 8

  ppp multilink interleave

LFI over Leased Line Configuration Example

The following example shows the configuration of LFI over a leased line. LFI must use an MLP bundle to be used over a leased line.

class-map voip

 match ip precedence 5

class-map business

 match ip precedence 3

policy-map llq-policy

 class voip

  priority 32

 class business

  bandwidth 32

policy-map input-policy

 class voip

  police 32000 1500 1500 conform-action transmit exceed-action drop

controller T1 5/1/0

 channel group 0 timeslots 1-2

interface multilink 2

 ip address 172.16.0.0 255.0.0.0

 keepalive 5

 bandwidth 128

 ppp multilink

 ppp multilink fragment-delay 8

 ppp multilink interleave

 service-policy output llq-policy

 service-policy input input-policy

 multilink-group 2

interface serial5/0/0:0

 no ip address

 encapsulation ppp

 keepalive 5

 ppp chap hostname G2

 ppp multilink

 multilink-group 2

Monitoring LFI Example

In the following example, the show ppp multilink command is used to monitor dLFI traffic. Note that this command output provides the numbers of fragmented, unfragmented, and reassembled packets entering and leaving the bundle.

Router# show ppp multilink 

Multilink11, bundle name is G11 

  Bundle is Distributed 

  0 lost fragments, 0 reordered, 0 unassigned 

  0 discarded, 0 lost received, 1/255 load 

  0x0 received sequence, 0x14 sent sequence 

  Member links:2 active, 0 inactive (max not set, min not set) 

    Serial4/1/1:2, no frags rcvd  64 weight, 2 max fragments 

    Serial4/1/1:3, no frags rcvd  64 weight, 2 max fragments 

dLFI statistics:

            DLFI Packets    Pkts In   Chars In   Pkts Out  Chars Out 

              Fragmented      20        1372        20       1372 

            UnFragmented       0         0          0          0   

             Reassembled       2         1228       2        1228 

        Reassembly Drops       0 

     Fragmentation Drops       0 

        Out of Seq Frags       0 

Additional References

The following sections provide references related to the Distributed Link Fragmentation and Interleaving over Leased Lines feature.

Related Documents

Related Topic	Document Title
Distributed Low Latency Queueing feature module.	Distributed Low Latency Queueing, Cisco IOS Release 12.1(5)T
Modular Quality of Service Command-Line Interface.	"Modular Quality of Service Command-Line Interface" section of the Cisco IOS Quality of Service Solutions Configuration Guide, Release 12.2
Quality of Service commands.	Cisco IOS Quality of Service Solutions Command Reference, Release 12.2
WAN configuration procedures.	Cisco IOS Wide-Area Networking Configuration Guide, Release 12.2
WAN commands: complete command syntax, command mode, defaults, usage guidelines, and examples.	Cisco IOS Wide-Area Networking Command Reference, Release 12.2
Distributed Multilink Point-to-Point Protocol for Cisco 7500 Series Router feature module.	Distributed Multilink Point-to-Point Protocol for Cisco 7500 Series Routers, Cisco IOS Release 12.0(3)T
Distributed Traffic Shaping feature module.	Distributed Traffic Shaping, Cisco IOS Release 12.1(5)T
Distributed Compressed Real-Time Transport Protocol feature module.	Distributed Compressed Real-Time Transport Protocol, Cisco IOS Release 12.1(5)T
Distributed Class-Based Weighted Fair Queueing feature module.	Distributed Class-Based Weighted Fair Queueing, Cisco IOS Release 12.1(5)T

Standards

Standard	Title
No new or modified standards are supported by this feature.	—

MIBs

MIBs	MIBs Link
No new or modified MIBs are supported by this feature, and support for existing MIBs has not been modified by this feature.	To locate and download MIBs for selected platforms, Cisco IOS releases, and feature sets, use Cisco MIB Locator found at the following URL: http://www.cisco.com/go/mibs

RFCs

RFCs	Title
RFC 1990	The PPP Multilink Protocol (MP)

Technical Assistance

Description	Link
Technical Assistance Center (TAC) home page, containing 30,000 pages of searchable technical content, including links to products, technologies, solutions, technical tips, and tools. Registered Cisco.com users can log in from this page to access more content.	http://www.cisco.com/public/support/tac/home.shtml

Command Reference

This section documents the modified ppp multilink interleave command. All other commands used with this feature are not new or modified and are documented in the Cisco IOS Release 12.2 command reference publications.

ppp multilink interleave

To enable interleaving of packets among the fragments of larger packets on a Multilink PPP (MLP) bundle, use the ppp multilink interleave interface configuration command. To disable interleaving, use the no form of this command.

ppp multilink interleave

no ppp multilink interleave

Syntax Description

This command has no arguments or keywords.

Defaults

Interleaving is disabled by default.

Command Modes

Interface configuration

Command History

Release	Modification
11.3	This command was introduced.
12.2(4)T3	This command was introduced on the VIP-enabled Cisco 7500 series routers as part of the Distributed Link Fragmentation and Interleaving feature. The Distributed Link Fragmentation and Interleaving feature introduced this command for ATM and Frame Relay only.
12.2(8)T	This command was introduced for leased lines for VIP-enabled Cisco 7500 series routers.
12.0(24)S	This command was introduced for leased lines for VIP-enabled Cisco 7500 series routers running Cisco IOS Release 12.0 S. This command cannot be used for ATM and Frame Relay using Cisco IOS Release 12.0 S.
12.2(14)SX	This command was introduced for leased lines for Cisco 7600 series routers and Catalyst 6500 series switches with a FlexWAN.
12.2(27)SBA	This command was integrated into Cisco IOS Release 12.2(27)SBA for leased lines for VIP-enabled Cisco 7500 series routers. This command cannot be used for ATM and Frame Relay in Cisco IOS Release 12.2(27)SBA.

Usage Guidelines

On the VIP-enabled Cisco 7500 series routers, distributed Cisco Express Forwarding (dCEF) must be enabled in order to use the ppp multilink interleave command. On the Cisco 7600series routers and Catalyst 6500 series routers, dCEF is enabled by default.

If interleaving is enabled when fragment-delay is not configured, then the default fragment size is 78 bytes of payload.

This command can only be configured using virtual template interfaces on VIP-enabled Cisco 7500 series routers for ATM and Frame Relay.

Examples

The following example shows the configuration of LFI using MLP over Frame Relay using a virtual template interface:

class-map voip

  match ip precedence 5

class-map business

  match ip precedence 3

policy-map llq-policy

  class voip

    priority 32

  class business

    bandwidth 32

policy-map shape-llq-policy

  class class-default

    shape average 80000 320 320

    service-policy llq-policy

policy-map input-policy

  class voip

    police 32000 1500 1500 conform-action transmit exceed-action drop

controller T1 5/1/0

  framing esf

  linecode b8zs

  channel-group 0 timeslots 1-2

interface Serial5/1/0:0

  no ip address

  encapsulation frame-relay

interface Serial5/1/0:0.1 point-to-point

  frame-relay interface-dlci 20 ppp Virtual-Template2

interface Virtual-Template2

  bandwidth 78

  ip address 98.0.0.2 255.0.0.0

  no keepalive

  service-policy output llq-policy

  service-policy input input-policy

  ppp multilink

  ppp multilink fragment-delay 8

  ppp multilink interleave

The following example shows the configuration of LFI using MLP on an ATM interface. This configuration uses a virtual template interface.

class-map voip

  match ip precedence 5

class-map business

  match ip precedence 3

policy-map llq-policy

  class voip

    priority 32

  class business

    bandwidth 32

policy-map input-policy

  class voip

    police 32000 1500 1500 conform-action transmit exceed-action drop

interface ATM4/0/0

  no ip address

  no atm ilmi-keepalive

interface ATM4/0/0.1 point-to-point

  pvc 0/34 

  abr 100 80

  protocol ppp Virtual-Template4

interface Virtual-Template4

  bandwidth 78

  ip address 88.0.0.2 255.0.0.0

  service-policy output llq-policy

  service-policy input input-policy

  ppp multilink

  ppp multilink fragment-delay 8

  ppp multilink interleave

The following example shows the configuration of LFI over a leased line. LFI must use an MLP bundle to be used over a leased line.

class-map voip

 match ip precedence 5

class-map business

 match ip precedence 3

policy-map llq-policy

 class voip

  priority 32

 class business

  bandwidth 32

policy-map input-policy

 class voip

  police 32000 1500 1500 conform-action transmit exceed-action drop

controller T1 5/1/0

 channel group 0 timeslots 1-2

interface multilink 2

 ip address 172.16.0.0 255.0.0.0

 keepalive 5

 bandwidth 128

 ppp multilink

 ppp multilink fragment-delay 8

 ppp multilink interleave

 service-policy output llq-policy

 service-policy input input-policy

 multilink-group 2

interface serial5/0/0:0

 no ip address

 encapsulation ppp

 keepalive 5

 ppp chap hostname G2

 ppp multilink

 multilink-group 2

Related Commands

Command	Description
show ppp multilink	Displays bundle information for the MLP bundles and their PPP links in the router.
ppp multilink fragment delay	Specifies a maximum size, in units of time, for packet fragments on an MLP bundle.

Glossary

CBWFQ—class-based weighted fair queueing. Extends the standard WFQ functionality to provide support for user-defined traffic classes.

class-based weighted fair queueing—See CBWFQ.

FIFO queueing—first-in, first-out queueing. FIFO involves buffering and forwarding of packets in the order of arrival. FIFO embodies no concept of priority or classes of traffic. There is only one queue, and all packets are treated equally. Packets are sent out an interface in the order in which they arrive.

FRF.8—The Frame Relay/ATM Interworking Implementation Agreement.

LFI—link fragmentation and interleaving. Method of fragmenting large packets and then queueing the fragments between small packets.

MLP—multilink PPP. Method of splitting, recombining, and sequencing datagrams across multiple logical links.

multilink PPP—See MLP.

QoS—quality of service. Measure of performance for a transmission system that reflects its transmission quality and service availability.

VC—virtual circuit. Logical circuit created to ensure reliable communication between two network devices. A VC is defined by a VPI/VCI pair and can be either permanent (PVC) or switched (SVC).

Voice over IP—method of transporting voice traffic over an IP network. In Voice over IP, the voice signal is segmented into frames, which are then coupled in groups of two and stored in voice packets. These voice packets are transported using a method that is in compliance with ITU-T specification H.323.

weighted fair queueing—See WFQ.

WFQ—weighted fair queueing. Congestion management algorithm that identifies conversations (in the form of traffic streams), separates packets that belong to each conversation, and ensures that capacity is shared fairly among these individual conversations. WFQ is an automatic way of stabilizing network behavior during congestion and results in increased performance and reduced retransmission.

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