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# Platform Considerations

You can configure cOCx/STMx interfaces on the following E-series routers:

- ERX-1440 router
- ERX-1410 router
- ERX-710 router
- ERX-705 router
- ERX-310 router

  | Note: The E320 router does not support configuration of channelized OCx/STMx interfaces.

For detailed information about the modules that support cOCx/STMx interfaces on ERX-7xx models, ERX-14xx models, and the ERX-310 router:

- See ERX Module Guide, Table 1, Module Combinations for detailed module specifications.
- See ERX Module Guide, Appendix A, Module Protocol Support for information about the protocols and applications that cOCx/STMx modules support.

## 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:

- 3 unchannelized/channelized DS3s per OC3
- 84 framed T1s per OC3/STM1
- 63 framed/unframed E1s per OC3/STM1
- 500 fractional T1/E1s per OC3/STM1

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

| 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 siutable 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:

- A fractional T1 or E1 line

  You assign channel groups of timeslots to configure fractional T1 or E1 over SONET/SDH VT on cOCx/STMx interfaces. A channel group is the fraction of the T1 or E1 line and comprises up to 24 T1 timeslots or up to 31 E1 timeslots. The default channel group speed for both T1 and E1 is 64 Kbps; 56 Kbps is also available.

- An unframed E1 line

  Unframed E1 lines have no timeslots reserved for framing. The router creates one channel for an unframed E1 line and assigns the number one to that channel.

  | Note: To configure a whole T1 or E1 line, assign 24 T1 or 31 E1 timeslots to a channel group or configure an unframed E1 line.

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

VT Type (SONET) | TU Name (SDH) | Number of Tributaries in a Group | Signal Standard
--- | --- | --- | ---
VT1.5 | TU-11 | 4 | T1
Not supported | TU-12 | 3 | E1

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

Figure 9: SONET Multiplexing

Figure 10: 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

Configuration | Identifier | Example
--- | --- | ---
Unframed E1 | pathChannel/pathPayload/tributaryGroup/ tributaryNumber/channelNumber | 10/1/2/2/1
NOTE: The router automatically assigns the channel number one to an unframed E1 line.
Fractional T1 or E1 | pathChannel/pathPayload/tributaryGroup/ tributaryNumber/channelGroup | 10/1/2/2/1

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

Identifier | Definition | Value
--- | --- | ---
pathChannel | An STS-1 or STM-1 line | A number in the range 1–2147483648
pathPayload | 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.
tributaryGroup | 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.
tributaryNumber | 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.
channelGroup | 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:

- An unchannelized T3 controller
- A T3 controller channelized to DS0 (fractional T1). To configure fractional T1 over T3 on cOCx/STMx interfaces, you assign timeslots (also known as subchannels) to the T1 channel. Each T1 channel supports 24 T1 timeslots.

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

Configuration | identifier | Example
--- | --- | ---
Unchannelized T3 | pathChannel/ds3- channel-number | 1/1
T3 channelized to DS0 | pathChannel/ds3Channel-number/ds1- channel-number/subchannelNumber | 1/1/10/15

### HDLC

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:

- slot—Number of the slot in which the line module resides in the chassis. In ERX-7xx models, line module slots are numbered 2-6 (slots 0 and 1 are reserved for SRP modules). In ERX-14xx models, line module slots are numbered 0–5 and 8–13 (slots 6 and 7 are reserved for SRP modules). In an ERX-310 router, line module slots are numbered 1–2 (slot 0 is reserved for the SRP module).
- port—Number of the port on the I/O module

  A cOC3/STM1 I/O module has four ports. Each port accepts one pair of SC-style fiber connectors.

  The cOC12/STM4 I/O module has one or two ports. On an I/O module that supports two ports, one port is active (primary) and the other is redundant. Cabling both ports provides a redundant path to the interface. If the active port fails, the redundant port automatically becomes active. You can configure only port 0 on a cOC12/STM4 I/O module. Port 0 accepts one pair of SC-style fiber connectors.

  On I/O modules that support APS/MSP, the port numbers for the working (primary) interfaces are assigned the lower half of the numbered interfaces, whereas the port numbers for the protect (redundant) interfaces are assigned the upper half of the numbered interfaces. For example, on an I/O module that provides one primary port and one redundant port, the working interface is port 0 and the protect interface is port 1.

- APS/MSP channel number—Identifier of the working or protect interface for configuration purposes

  The protect interface is always assigned channel number 0. The working interface is always assigned channel number 1.

For information about installing line modules and I/O modules in ERX routers, see ERX Hardware Guide, Chapter 4, Installing Modules.

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