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Configuring SAToP Emulation on Channelized T1 and E1 Interfaces


This configuration is the base configuration of SAToP on an ACX Series router as described in RFC 4553, Structure-Agnostic Time Division Multiplexing (TDM) over Packet (SAToP). When you configure SAToP on built-in channelized T1 and E1 interfaces, the configuration results in a pseudowire that acts as a transport mechanism for the T1 and E1 circuit signals across a packet-switched network.

The network between the customer edge (CE) routers appears transparent to the CE routers, making it seem that the CE routers are directly connected. With the SAToP configuration on the provider edge (PE) router’s T1 and E1 interfaces, the interworking function (IWF) forms a payload (frame) that contains the CE router’s T1 and E1 Layer 1 data and control word. This data is transported to the remote PE over the pseudowire. The remote PE removes all the Layer 2 and MPLS headers added in the network cloud and forwards the control word and the Layer 1 data to the remote IWF, which in turn forwards the data to the remote CE.

Figure 1: Pseudowire Encapsulation with SAToP
Pseudowire Encapsulation
with SAToP

In Figure 1 the Provider Edge (PE) router represents the ACX Series router that is being configured in these steps. The result of these steps is the pseudowire from PE1 to PE2. Topics include:

Setting the T1/E1 Emulation Mode

Emulation is a mechanism that duplicates the essential attributes of a service (such as T1 or E1) over a packet-switched network. You set the emulation mode so that the built-in channelized T1 and E1 interfaces on the ACX Series router can be configured to work in either T1 or E1 mode. This configuration is at the PIC level, so all ports operate as either T1 interfaces or E1 interfaces. A mix of T1 and E1 interfaces is not supported. By default all the ports operate as T1 interfaces.

  • Configure the emulation mode:

    [edit chassis fpc fpc-slot pic pic-slot]

    user@host# set framing (t1 | e1)

    For example:

    [edit chassis fpc 0 pic 0]

    user@host# set framing t1

    After a PIC is brought online and depending on the framing option used (t1 or e1), on the ACX2000 router, 16 CT1 or 16 CE1 interfaces are created, and on the ACX1000 router, 8 CT1 or 8 CE1 interfaces are created.

    The following output shows this configuration:

    The following output from the show interfaces terse command shows the 16 CT1 interfaces created with the framing configuration.


If you set the framing option incorrectly for the PIC type, the commit operation fails.

If you change the mode, the router will reboot the built-in T1 and E1 interfaces.

Bit error rate test (BERT) patterns with all ones received by T1 and E1 interfaces configured for SAToP do not result in an alarm indication signal (AIS) defect. As a result, the T1 and E1 interfaces remain up.

Configuring One Full T1 or E1 Interface on Channelized T1 and E1 Interfaces

You must configure a child T1 or E1 interface on the built-in channelized T1 or E1 interface created because the channelized interface is not a configurable interface and SAToP encapsulation must be configured (in the next step) for the pseudowire to function. The following configuration creates one full T1 interface on the channelized ct1 interface. You can follow the same process to create one E1 interface on the channelized ce1 interface.

  • Configure one full T1/E1 interface:

    [edit interfaces ct1-fpc/pic /port]

    user@host# set no-partition interface-type (t1 | e1)

    For example:

    [edit interfaces ct1-0/0/0

    user@host# set no-partition interface-type t1

    The following output shows this configuration:

The preceding command creates the t1-0/0/0 interface on the channelized ct1-0/0/0 interface. Check the configuration with the show interfaces interface-name extensive command. Run the command to display output for the channelized interface and the newly created T1 or E1interface. The following output provides an example of the output for a CT1 interface and the T1 interface created from the preceding example configuration. Notice that ct1-0/0/0 is running at T1 speed and that the media is T1.

In the following output for the T1 interface, the parent interface is shown as ct1-0/0/0 and the link level type and encapsulation are TDM-CCC-SATOP.

Setting the SAToP Encapsulation Mode

The built-in T1 and E1 interfaces must be configured with SAToP encapsulation at the PE router so that the interworking function (IWF) can segment and encapsulate TDM signals into SAToP packets, and in the reverse direction, to decapsulate the SAToP packets and reconstitute them into TDM signals.

  1. On the PE router, configure SAToP encapsulation on the physical interface:

    [edit interfaces (t1 | e1)–fpc/pic /port]

    user@host# set encapsulation satop

    For example:

    [edit interfaces t1-0/0/0

    user@host# set encapsulation satop

  2. On the PE router, configure the logical interface:

    [edit interfaces ]

    user@host# set (t1 | e1)–fpc/pic/port unit logical-unit-number

    For example:

    [edit interfaces]

    user@host# set t1-0/0/0 unit 0

    It is not necessary to configure the circuit cross-connect (CCC) family because it is automatically created for the preceding encapsulation. The following output shows this configuration.

Configure the Layer 2 Circuit

When you configure the Layer 2 circuit, you designate the neighbor for the provider edge (PE) router. Each Layer 2 circuit is represented by the logical interface connecting the local PE router to the local customer edge (CE) router. All the Layer 2 circuits that use a particular remote PE router, designated for remote CE routers, are listed under the neighbor statement. Each neighbor is identified by its IP address and is usually the end-point destination for the label-switched path (LSP) tunnel that transports the Layer 2 circuit. Configure the Layer 2 circuit:

  • [edit protocols l2circuit neighbor address]

    user@host# set interface interface-name virtual-circuit-id identifier

    For example, for a T1 interface:

    [edit protocols l2circuit neighbor

    user@host# set interface t1-0/0/0.0 virtual-circuit-id 1

    The preceding configuration is for a T1 interface. To configure an E1 interface, use the E1 interface parameters. The following output shows this configuration.