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Configuring the E3 CSU Compatibility Mode


Subrating an E3 interface reduces the maximum allowable peak rate by limiting the High-level Data Link Control (HDLC)-encapsulated payload. Subrate modes configure the PIC to connect with channel service units (CSUs) that use proprietary methods of multiplexing.

On M Series and T Series routers, you can configure E3 interfaces to be compatible with a Digital Link, Kentrox, or Larscom CSU.


To subrate an E3 interface to be compatible with a Kentrox CSU, you must have an IQ-based PIC. Non-IQ PICs allow a commit of the configuration, but the interfaces remain at the full E3 rate for the Kentrox compatibility mode.

For E3 interfaces on IQE PICs, subrate is not supported and the E3-options compatibility-mode and payload-scrambler are invalid. Although Junos OS CLI allows a commit of this configuration, the interfaces remain at the full E3 rate and implicitly default to only Kentrox compatibility mode.

To configure an E3 interface so that it is compatible with the CSU at the remote end of the line, include the compatibility-mode statement at the [edit interfaces interface-name e3-options] hierarchy level:

The subrate of an E3 interface must exactly match that of the remote CSU. To specify the subrate, include the subrate statement in the configuration:

  • For Kentrox CSUs, specify the subrate as a number from 1 through 48 that exactly matches the value configured on the CSU. Each increment of the subrate value corresponds to a rate increment of about 0.5 Mbps.

  • For Digital Link CSUs, you can specify the subrate value to match the data rate configured on the CSU in the format xkb or x.xMb. You can configure the subrate values shown in Table 1.

  • Larscom CSUs do not support the E3 subrate.

Table 1: Subrate Values for E3 Digital Link Compatibility Mode

358 Kbps

7.2 Mbps

14.0 Mbps

20.8 Mbps

27.6 Mbps

716 Kbps

7.5 Mbps

14.3 Mbps

21.1 Mbps

27.9 Mbps

1.1 Mbps

7.9 Mbps

14.7 Mbps

21.5 Mbps

28.3 Mbps

1.4 Mbps

8.2 Mbps

15.0 Mbps

21.8 Mbps

28.6 Mbps

1.8 Mbps

8.6 Mbps

15.4 Mbps

22.2 Mbps

29.0 Mbps

2.1 Mbps

9.0 Mbps

15.8 Mbps

22.6 Mbps

29.4 Mbps

2.5 Mbps

9.3 Mbps

16.1 Mbps

22.9 Mbps

29.7 Mbps

2.9 Mbps

9.7 Mbps

16.5 Mbps

23.3 Mbps

30.1 Mbps

3.2 Mbps

10.0 Mbps

16.8 Mbps

23.6 Mbps

30.4 Mbps

3.6 Mbps

10.4 Mbps

17.2 Mbps

24.0 Mbps

30.8 Mbps

3.9 Mbps

10.7 Mbps

17.5 Mbps

24.3 Mbps

31.1 Mbps

4.3 Mbps

11.1 Mbps

17.9 Mbps

24.7 Mbps

31.5 Mbps

4.7 Mbps

11.5 Mbps

18.3 Mbps

25.1 Mbps

31.9 Mbps

5.0 Mbps

11.8 Mbps

18.6 Mbps

25.4 Mbps

32.2 Mbps

5.4 Mbps

12.2 Mbps

19.0 Mbps

25.8 Mbps

32.6 Mbps

5.7 Mbps

12.5 Mbps

19.3 Mbps

26.1 Mbps

32.9 Mbps

6.1 Mbps

12.9 Mbps

19.7 Mbps

26.5 Mbps

33.3 Mbps

6.4 Mbps

13.2 Mbps

20.0 Mbps

26.9 Mbps

33.7 Mbps

6.8 Mbps

13.6 Mbps

20.4 Mbps

27.2 Mbps


For information about subrating a T3 interface, see Configuring the T3 CSU Compatibility Mode.