Platform Considerations

You can configure cOCx/STMx interfaces on the following E Series Broadband Services Routers:

For detailed information about the modules that support cOCx/STMx interfaces on ERX7xx models, ERX14xx models, and the ERX310 router:

cOCx/STMx FO Line Module

The cOCx/STMx F0 line module pairs with either a cOC3/STM1 I/O module or a cOC12/STM4 I/O module to support channelized T3 (DS3), T1, E1, FT1, and FE1 signaling. Each connection is made through standard SC connectors.

The cOCx/STMx line module supports the following:

You can combine the cOCx/STMx line module with four-port cOC3/STM1 I/O modules or one-port cOC12/STM4 I/O modules. cOC3/STM1 I/O modules support one OC3/STM1 per port. cOC12/STM4 I/O modules support all four OC3/STM1s on one port.

The cOCx/STMx line module and its corresponding I/O modules can support either E1 or T1 operation. These modules cannot support E1 and T1 operation simultaneously.

Interface Stack

Figure 8 shows the stack for cOCx/STMx interfaces.

Figure 8: Stack for cOCx/STMx Interfaces

Stack for cOCx/STMx Interfaces

Note: For a detailed description of interface types and specifiers, see Interface Types and Specifiers in JunosE Command Reference Guide. For information about interfaces, see Planning Your Network in JunosE System Basics Configuration Guide.

The section layer manages the transport of STS/STM frames across the physical path. This layer is responsible for frame alignment, scrambling, error detection, error monitoring, signal reception, and signal regeneration.

The line layer manages the transport of SONET/SDH payloads, which are embedded in a sequence of STS/STM frames in the physical medium. This layer is responsible for multiplexing and synchronization.

The path layer maps the user payload into a SONET/SDH format suitable for the line layer. This layer transports the actual network services (such as T1s and T3s) between SONET/SDH multiplexing devices and provides end-to-end transmission.

When you configure a cOCx/STMx interface, be sure you understand its position in the SONET or SDH hierarchy. This implementation of SONET and SDH uses the term path to identify an STS-1 or STM-1 line. You must know how to identify the path for the configuration and the higher-level controllers, such as T3 or unframed E1 over SONET VT.

SONET/SDH VT Controllers

SONET/SDH VT on cOCx/STMx interfaces support these options:

To identify a controller over SONET/SDH VT, you must consider the multiplexing for SONET and SDH virtual tributaries. In SONET, an STS-1 frame can be divided into seven virtual tributary (VT)groups. Similarly, for SDH, an STM-0 frame can be divided into seven tributary units (TUs). Each group or unit contains a number of virtual tributaries; that number depends on the VT type or TU name. Table 10 lists the VT types and TU names that the router supports.

Table 10: Tributary Standards That cOCx/STMx Interfaces Support


TU Name (SDH)

Number of Tributaries in a Group

Signal Standard





Not supported




Figure 9 shows the structure for SONET, and Figure 10 shows the structure for SDH.

Figure 9: SONET Multiplexing

SONET Multiplexing

Figure 10: SDH Multiplexing

SDH Multiplexing

For both SONET/SDH VT configurations, you must identify the path and controllers above the path layer. Table 11 shows the identifiers for these configurations, and Table 12 provides definitions for the identifiers.

Table 11: Identifiers for SONET/SDH VT Controllers




Unframed E1



NOTE: The router automatically assigns the channel number one to an unframed E1 line.

Fractional T1 or E1



Table 12: Definitions for Identifiers for SONET/SDH VT Controllers





An STS-1 or STM-1 line

A number in the range 1–2147483648


Number of the payload within the path

In SONET mode, pathPayload is always 1. In SDH mode, pathPayload is the number of the TUG-3 group.


Number of the tributary group within the path

In SONET mode, tributary group is the number of the VT group. In SDH mode, tributaryGroup is the number of the TUG-2 group.


Number of the tributary within the group

In SONET mode, tributaryNumber is the number of the VT. In SDH mode, tributaryNumber is the number of the TUG-1 group or tributary unit.


A fraction of a T1 or an E1 line

A number in the range 1-24 for T1 or 1-31 for E1

T3 Controllers

You can configure the STS-1 frame to carry a single T3 signal through asynchronous mapping. As Figure 9 shows, T3 on cOCx/STMx interfaces supports the following options:

For any configuration, you must identify the path and each controller in the layers above the path layer. For example, for a T3 controller channelized to T1, you must identify the path channel, the T3 channel, and the T1 channel. Table 13 presents the identifiers for the T3 configurations.

Table 13: Identifiers for T3 Controllers




Unchannelized T3



T3 channelized to DS0




You must configure HDLC over the T3, unframed E1, or fractional T1/E1 line that you configure on an interface. As Figure 8 shows, HDLC is at the top layer of the interface stack.

Numbering Scheme

A cOCx/STMx interface is identified by the slot/port format, where:

For information about installing line modules and I/O modules in ERX routers, see the Installing Modules chapter in the ERX Hardware Guide.