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# Platform Considerations

You can configure channelized T3 interfaces on the following E-series routers:

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

  | Note: The E120 router and the E320 router do not support configuration of channelized T3 interfaces.

For detailed information about the modules that support channelized T3 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 channelized T3 modules support.

## CT3/T3-F0 Line Modules and CT3/T3 12 I/O Modules

ERX-7xx models, ERX-14xx models, and the ERX-310 router support the CT3/T3-F0 line module and CT3/T3 12 I/O module. The CT3/T3-F0 line module and CT3/T3 12 I/O module support both channelized and unchannelized T3 operation. You can configure a mixture of channelized and unchannelized ports on these modules. For information about configuring unchannelized T3 ports, see Configuring Channelized T3 Interfaces.

ERX-14xx models support up to 12 CT3/T3-F0 line modules and 12 CT3/T3 12 I/O modules, ERX-7xx models support up to 5 CT3/T3-F0 line modules and 5 CT3/T3 12 I/O modules, and the ERX-310 router supports up to two CT3/T3-F0 line modules and two CT3/T3 12 I/O modules. Each CT3/T3 12 I/O module has 12 physical T3 (DS3) ports. Each port uses two SMB connectors: one for the transmit (TX) connection and one for the receive (RX) connection.

CT3/T3-F0 line modules and CT3/T3 12 I/O modules support the following in channelized mode:

- 28 asynchronous T1 (DS1) channels per T3 port
- 24 DS0 channels (64-Kbps) per T1 interface
- 166 DS0 channels per T3 port

## Exchanging Modules

If you replace a CT3/T3 line module and a CT3/T3 I/O module with a CT3/T3-F0 line module and a CT3/T3 12 I/O module or vice versa, you must erase the configuration of the existing modules. See the slot accept command in Managing Modules in the JUNOSe System Basics Configuration Guide.

## Interface Stack

Figure 1 shows the stack for a channelized T3 interface. To configure a channelized T3 interface, configure a T3 controller, followed by a T1 channel, and then a fractional T1 channel. Finally, you must configure a High-Speed Data Link Control (HDLC) data channel on the interface.

Figure 1: Stack for Channelized T3 Interface

For more information about the layers in a channelized T3 interface, see Numbering Scheme.

| 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.

## Numbering Scheme

This section describes how to identify each layer in a channelized T3 interface stack.

### T3 Controllers

A T3 controller on a channelized T3 interface is identified using 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 0–2; slot 0 is reserved for the SRP module.

- port—Number of the port on the I/O module. On a CT3/T3 12 I/O module, ports are numbered 0–11.

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

### T1 Channels

A T3 line consists of 28 T1 channels (or data streams). A T1 channel is identified by its number in the range 1–28.

Each T1 channel is an aggregate of 24 DS0 timeslots, as shown in Figure 2. To configure an entire T1 line, assign 24 timeslots to each channel.

Figure 2: T1 Channels and DS0 Timeslots on a T3 Line

### Fractional T1

Fractional T1 is a portion of a T1 line. To configure fractional T1 on a channelized T3 interface, you assign a range of DS0 timeslots to a T1 channel and subchannel. A subchannel is group of timeslots. Subchannel numbers range from 1–24 and do not necessarily correspond to DS0 timeslots. The subchannel number identifies a fractional T1 channel.

For example, you might make the assignments for subchannels 1–6 as listed in Table 4.

Table 4: Sample T1 Subchannel/Timeslot Assignments

Subchannel | DS0 Timeslot
--- | ---
1 | 1–4, 10, 22–24
2 | 5–6
3 | 7–9
4 | 11
5 | 12–15, 20–21
6 | 16–19

To configure the subchannels listed in Table 4, use the following command to specify the T3 controller in chassis slot 0, port 1.

`

host1(config)#controller t3 0/1

`

Then assign the timeslots to channel 1, subchannel 1.

`

host1(config-controll)#t1 1/1 timeslots 1-4,10,22-24
host1(config-controll)#t1 1/2 timeslots 5-6
host1(config-controll)#t1 1/3 timeslots 7-9
host1(config-controll)#t1 1/4 timeslots 11
host1(config-controll)#t1 1/5 timeslots 12-15,20-21
host1(config-controll)#t1 1/6 timeslots 16-19

`

### HDLC Channels

To identify an HDLC channel or the complete channelized T3 interface, use the format slot/port:T1 channel/subchannel. Refer to the preceding sections for definitions of the variables.

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