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Configuring Inverse Multiplexing for ATM (IMA) on ACX Series

 

Inverse multiplexing for ATM (IMA) is a standardized technology used to transport ATM traffic over a bundle of T1 or E1 interfaces, also known as an IMA Group, allowing for an increase in the bandwidth capacity. When you configure IMA on ACX Series routers, you must configure the following:

  • The aggregated device count—The device count is the number of IMA group interfaces created on the CT1 or CE1 interfaces. The logical ATM interface that is part of the IMA group has the following naming format: at-fpc/pic/port with the port number taken from the last port on the MIC plus 1. For example, on the ACX2000 router with a 16-port built-in T1/E1 TDM MIC, the IMA group interface numbering starts with at-0/0/16 and increments by 1 to at-0/0/17, and so on. On the ACX1000 router with an 8-port built-in T1/E1 TDM MIC, the IMA group interface numbering starts with at-0/0/8 and increments by 1 to at-0/0/9, and so on

  • The framing mode—Emulation is a mechanism that duplicates the essential attributes of a service, such as T1 or E1, over a packet-switched network. The built-in channelized T1 and E1 interfaces (CT1 and CE1) on the ACX Series routers can be configured to work in either T1 or E1 mode, and these child T1 and E1 interfaces can be configured to carry ATM services over the packet-switched network.

  • One full T1 or E1 interface on the channelized CT1 or CE1 interface—The built-in channelized interface is a non-configurable interface that requires a child T1 or E1 or ATM interface on which you configure the parameters.

  • The T1 or E1 interface as a member of the IMA group of the respective IMA link—Each child T1 or E1 interface of a channelized CT1 or CE1 interface is the physical interface over which the ATM signals are carried. This T1 or E1 interface must be specified as a member of an IMA group so that the IMA link will work.

  • IMA group interface configuration—Each IMA group interface (at-fpc/pic/port) must be configured with all ATM properties for it to work properly: logical link-layer encapsulation type, the circuit cross-connect protocol suite, and the entire ATM device must be dedicated to the ATM cell relay circuit.

The following sections explain how to create an ATM IMA group and to configure it according to your requirements:

The following sections explain how to create an ATM IMA group and to configure it according to your requirements:

Creating an IMA Group (ATM Interfaces)

To create an IMA group, perform the following steps:

  1. In configuration mode, go to the [edit chassis] hierarchy level:
  2. Configure the Flexible Port Concentrator (FPC) slot and the Physical Interface Card (PIC) slot as needed.
  3. Configure the device count. The device count can be set starting from 1 through 42 in the aggregated device options for inverse multiplexing for ATM at the [edit chassis fpc fpc-slot pic pic-slot] hierarchy level.

This results in the creation of interfaces from at-x/y/g through at-x/y/g+count–1, where the variable count is the number of interfaces and the variable g is picked from 16 onwards.

The PIC is automatically rebooted when a configuration that changes the IMA group count is committed.

Configuring Group ID for an IMA Link on a T1 Interface or an E1 Interface

A group ID is assigned to all links in an IMA group.

To assign a group ID to a T1 or an E1 interface:

  1. In configuration mode, go to the [edit interfaces interface-name] hierarchy level, where the interface name is t1-fpc/pic/port:m:n, e1-fpc/pic/port:n, or t1|e1-fpc/pic/port.
  2. Configure the encapsulation as ima.
  3. Configure the IMA group ID from 16 through 57. Note that this group ID is the same for all T1/E1 interfaces for a particular ATM IMA interface.

Implement the aforementioned procedure to apply a group ID for all applicable T1 or E1 interfaces.

Configuring ATM Encapsulation Options

To configure the logical link-layer encapsulation for an ATM interface to support IMA:

  1. In configuration mode, go to the [edit interfaces interface-name] hierarchy level, where the interface name is at-fpc/pic/port.
  2. Configure the logical interface (unit) as 0 and set the encapsulation for this logical interface as either ATM cell relay for CCC or ATM VC for CCC.

Configuring IMA Group Options

To configure the various options for an IMA group on an ATM interface:

  1. In configuration mode, go to the [edit interfaces interface-name ima-group-options] hierarchy level, where the interface name is at-fpc/pic/port.
  2. Configure the maximum differential delay between the links in the IMA group. You can configure the maximum differential delay from 1 millisecond through 56 milliseconds. By default, 25 milliseconds is set.
  3. Configure the frame length of the ICP cell as 32, 64, 128, or 256. By default, 128 is set.
  4. Configure the IMA group frame synchronization state parameters alpha, beta, and gamma.

    For the default values and parameter range for alpha, beta, and gamma, see Understanding ATM IMA Configuration on ACX Series Router.

  5. Configure IMA group minimum active links. You can configure between 1 to 16 links. 1 is set by default.
  6. Configure the symmetry of the IMA group as either symmetrical configuration and operation or symmetrical configuration and asymmetrical operation.

    For information about symmetry, see Understanding ATM IMA Configuration on ACX Series Router.

  7. Configure a test procedure to start and end the test pattern procedure.

    For information about test procedure, see Understanding ATM IMA Configuration on ACX Series Router.

  8. Configure a transmit clock to reflect the primary reference source (PRS) of the clock for each link in a group either in common timing mode or independent timing mode. By default, common timing mode is selected.
  9. Configure the IMA specification version as either version 1.0 or version 1.1. By default, IMA version 1.1 is selected.