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ATM IMA Configuration Overview

 

Inverse multiplexing for ATM (IMA) involves inverse multiplexing and demultiplexing of ATM cells in a round-robin sequence among links grouped to form a higher-bandwidth logical link whose rate is the sum of all the link rates. This group of links is called an IMA group. An IMA group can also be defined as a group of links at the transmitting end that is used to establish an IMA virtual link to the receiving end. The IMA virtual link is a virtual link that is established between two IMA units or routers over a number of physical links (in an IMA group). IMA groups terminate at each end of the IMA virtual link.

You can configure 42 IMA groups. Each group can contain from 1 through 32 links.

You can configure a maximum of 16 IMA groups on the 16-port Channelized E1/T1 Circuit Emulation MIC (MIC-3D-16CHE1-T1-CE) and each group can have from 1 through 8 IMA links. Port numbers starting from 0 through 15 are used for T1/E1 ports; therefore, IMA port numbers start from 16 onward. For information about MIC-3D-16CHE1-T1-CE, see Channelized E1/T1 Circuit Emulation MIC.

You can configure a maximum of 42 IMA groups on the 4-port Channelized OC3/STM1 (Multi-Rate) Circuit Emulation MIC with SFP (MIC-3D-4COC3-1COC12-CE). The IMA port numbers start from 16 onward. For information about MIC-3D-4COC3-1COC12-CE, see Channelized OC3/STM1 (Multi-Rate) Circuit Emulation MIC with SFP.

To configure an IMA group, execute the set chassis fpc fpc-slot pic pic-slot aggregated devices ima device-count count configuration command, where count results in the creation of interfaces from at-x/y/g through at-x/y/g+count-1. The variable g is chosen such that there is no conflict with non-IMA ATM interfaces on the same PIC. For example, if the count variable is set to 4, then the new ATM interfaces are created from at-x/y/16 through at-x/y/19.

You can implement inverse multiplexing for ATM (IMA) on Juniper Networks routers by configuring an IMA group and its options. The following sections explain the various options that can be set for an IMA group:

IMA Version

Either IMA 1.0 (af-phy-0086.000-IMA) or IMA 1.1 (af-phy-0086.001-IMA) can be selected through the CLI. To choose the IMA specification version, execute the set interfaces interface-name ima-group-options (1.0|1.1) configuration command. Note that, if you do not specify the version, IMA 1.1 is selected by default.

IMA 1.0 and IMA 1.1 do not interoperate.

The IMA v1.1 specification increments the operations and maintenance (OAM) label value used in the IMA OAM cells in order to differentiate v1.1 from v1.0 IMA units.

IMA Frame Length

An IMA frame consists of ATM cells, an ICP cell, and filler cells (if required). When you configure an IMA group, you can choose a frame length of 32, 64, 128, or 256. The frame length can be selected independently in each direction and in each group. To set the frame length, execute the set interface interface-name frame-length (32 |64 |128 |256) configuration command. Note that if the frame length is not specified, the frame length value of 128 is selected by default.

Transmit Clock

When you create an IMA group, you can configure a common transmit clock timing mode or an independent transmit clock timing mode to reflect the primary reference source (PRS) of the clock for each link in a group. By default, the common mode is selected. To select the transmit clock timing mode, execute the set interface interface-name ima-group-options transmit-clock (common | independent) configuration command.

IMA Group Symmetry

You can configure an IMA group to allow symmetric or asymmetric cell rate transfer over an IMA virtual link. You can configure the IMA group with one of the following modes:

  • Symmetrical configuration and operation—In this mode, on the ATM IMA device, an IMA link must be configured in each direction for all physical links that the ATM IMA device is configured to use. In this mode, the ATM IMA device can transmit and receive ATM layer cells over the physical links on which the IMA links running in both directions are Active.

  • Symmetrical configuration and asymmetrical operation—In this mode, on the ATM IMA device, an IMA link must be configured in each direction for all physical links that the ATM IMA device is configured to use. In this mode, the ATM IMA device can transmit ATM layer cells over the physical links on which the IMA links in the transmit direction are Active, while the IMA links in the receive direction are not Active or contrariwise.

Asymmetrical configuration and operation are not supported.

The mode can be configured through the CLI when an IMA group is created. To select the symmetry option, execute the set interface interface-name ima-group-options symmetry (symmetrical-config-and-operation | symmetrical-config-asymmetrical-operation) configuration command. By default, symmetrical configuration and operation is selected.

Minimum Active Links

You can set the minimum active links for an IMA group from 1 through 32.

  • PTx is the minimum number of links required to be active in the transmit direction for the IMA group to move into the operational state.

  • PRx is the minimum number of links required to be active in the receive direction for the IMA group to move into the operational state.

You configure PTx and PRx through the CLI when an IMA group is created. By default, 1 is selected.

For a symmetrical configuration, PTx is equal to PRx.

To set minimum links, execute the set interface interface-name ima-group-options minimum-links links configuration command. By default, symmetrical configuration and operation is selected.

State Transition Variables: Alpha, Beta, and Gamma

Frame synchronization is a process of recovery of the aggregated frames. The frame synchronization states form a basis for the different error and maintenance states. You can configure the IMA frame synchronization link state transition variables as alpha, beta, and gamma. The valid ranges and default values are shown in Table 1.

Setting

Range

Default

Description

alpha

1–2

2

Consecutive invalid ICP cells

beta

1–5

2

Consecutive errored ICP cells

gamma

1–5

1

Consecutive valid ICP cells

To set the frame synchronization option, execute the set interface interface-name ima-group-options frame-synchronization alpha number beta number gamma number configuration command.

IMA Link Addition and Deletion

When an IMA group is up, you can add links to or delete links from the group without dropping cells.

To create an IMA link, you must:

  • Configure the encapsulation as ima at the [edit interfaces interface-name encapsulation] hierarchy level.

  • Configure an ATM interface with one T1 link or one E1 link with the set interfaces interface-name ima-link-options group-id g configuration command.

The interface-name variable refers to the T1 or E1 interface to be set as an IMA interface link and the variable g refers to the port in the at-x/y/g interface.

To delete the configured IMA link, you must execute the following configuration commands:

  • delete interfaces interface-name encapsulation ima

  • delete interfaces interface-name ima-link-options group g

IMA Test Pattern Procedure

A test pattern procedure is supported for IMA to test the ATM, T1, and E1 interfaces for irregularities. You can use the CLI to start and end the test pattern procedure.

The following options can be set according to the requirement at the [edit interface interface-name ima-group-options test-procedure] hierarchy level:

  • interface interface-name—Interface name of the IMA link to test.

  • pattern number—IMA test pattern that can be set from 1 through 254

  • period number—Length of the IMA test pattern that can be set from 1 second through 4,294,967,294 seconds.

To perform the test pattern procedure, execute the test interface interface-name ima-test-start and test interface interface-name ima-test-stop operational mode commands to start and to stop the IMA test, respectively.

Per-PIC Limit on the Number of Links

The per-PIC limit on the number of links with the 12-port E1/T1 Circuit Emulation PIC (PB-12T1E1-CE-TELCO) is up to 12 T1 or E1 links.

The per-PIC limits on the number of links with the 4-port Channelized OC3/STM1 Circuit Emulation PIC with SFP (PB-4CHOC3-CE-SFP) are:

  • T1—0 through 168

  • E1—0 through 126

  • Mixed: total bandwidth limited to 2xOC3; 258,048,000 bps

The per-PIC limits on the number of links with the 4-port Channelized OC3/STM1 (Multi-Rate) Circuit Emulation MIC with SFP (MIC-3D-4COC3-1COC12-CE) are:

  • T1—0 through 336

  • E1—0 through 252

IMA Group Alarms and Group Defects

Table 2 shows the supported IMA group alarms and their associated IMA standard requirement numbers. This is displayed in the group status and control field of an ICP cell.

Table 2: IMA Group Alarms with IMA Standard Requirement Numbers

Alarm

IMA Standard Requirement Number

Start-up-FE

R-145

Config-Aborted

R-146

Config-Aborted-FE

R-147

Insufficient-Links

R-148

Insufficient-Links-FE

R-149

Blocked-FE

R-150

GR-Timing-Mismatch

R-151

Table 3 shows the supported IMA group defects and their associated IMA standard requirement numbers. This is displayed in the group status and control field of an ICP cell.

Table 3: IMA Group Defects with IMA Standard Requirement Numbers

Defects

IMA Standard Requirement Number

Start-up-FE

R-145

Config-Aborted

R-146

Config-Aborted-FE

R-147

Insufficient-Links

R-148

Insufficient-Links-FE

R-149

Blocked-FE

R-150

GR-Timing-Mismatch

R-151

IMA Link Alarms and Link Defects

Table 4 shows the supported IMA link alarms that are reported to the IMA unit management with their associated IMA standard requirement numbers.

Alarm

IMA Standard Requirement Number

Description

LIF

R-138

Loss of IMA frame

LODS

R-139

Link out of delay synchronization

RFI-IMA

R-140

Remote defect/failure

Tx-Mis-Connected

R-141

Transmit misconnected

Rx-Mis-Connected

R-142

Receive misconnected

Tx-Unusable-FE

R-143

Transmit unusable far end

Rx-Unusable-FE

R-144

Receive unusable far end

Link Fault

Link fault

An IMA unit management is defined by SNMP MIBs.

Table 5 shows the supported IMA link defects that are reported to the unit management with their associated IMA standard requirement numbers.

Defect

IMA Standard Requirement Number

Description

LIF

R-138

Loss of IMA frame

LODS

R-139

Link out of delay synchronization

RFI-IMA

R-140

Remote defect/failure

Tx-Mis-Connected

R-141

Transmit misconnected

Rx-Mis-Connected

R-142

Receive misconnected

Tx-Unusable-FE

R-143

Transmit unusable far end

Rx-Unusable-FE

R-144

Receive unusable far end

Link Fault

Link fault

IMA Group Statistics

You can use the show interfaces command to display the following IMA group statistics:

  • Near-end failure count

  • Far-end failure count

  • Receive end (Rx) faulty cells due to address mismatch

  • Running seconds

  • Unavailable seconds

For more information about IMA group statistics, see the show interfaces command description in the CLI Explorer.

IMA Link Statistics

Table 6 shows the IMA link statistics.

Performance Parameter

IMA Standard Requirement Number

Rx LIF

Rx ICP cells

Rx errored ICP cells

R-106

Rx LODS

R-106

Rx ICP violation

R-107

Rx stuff

O-17

Near-end Rx SES

R-108

Near-end Rx UAS

R-110

Near-end Rx UUS

R-113

Near-end Rx failure

R-117

Near-end Tx failure

Far-end Rx SES

R-109

Far-end Rx UAS

R-111

Far-end Rx UUS

R-115

Far-end defects

Far-end Rx failure

Tx ICP cells

Tx stuff

O-16

Near-end Tx UUS

R-112

Far-end Tx UUS

R-114

Far-end Tx failure

IMA Clocking

Interface clock source is applicable only to IMA links.

You can set the interface clock source as external or internal with the set interfaces at-x/y/z clocking (external | internal) configuration command. Note that the clocking statement is not applicable to the at-x/y/g interface because the IMA group it represents is a virtual interface.

Differential Delay

You can set the maximum differential delay from 1 millisecond through 56 milliseconds among links in an IMA group. By default, a differential delay of 25 milliseconds is set. Execute the set interfaces interface-name ima-group-options differential-delay delay configuration command to set the differential delay.