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Enabling SONET Payload Scrambling


This section includes the following information to assist you when troubleshooting SONET interfaces:

Checklist for Enabling SONET Payload Scrambling

Table 1 provides links and commands for SONET payload scrambling and how to check and configure it.

Table 1: Checklist for Enabling SONET Payload Scrambling


Command or Action

Understanding SONET Payload Scrambling
  1. Checking SONET HDLC Payload Scrambling

show configuration interfaces | interface-name

show interfaces interface-name

  1. Configuring SONET HDLC Payload Scrambling


edit interfaces so-fpc/pic/port sonet-options

set payload-scrambler



Understanding SONET Payload Scrambling

SONET payload scrambling preserves data integrity. Scrambling is designed to randomize the digital bits (pattern of 1s and 0s) carried in the Asynchronous Transfer Mode (ATM) cells (physical layer frame). Randomizing the digital bits can prevent continuous, long strings of all 1s or all 0s. Transitions between 1s and 0s are used by some physical layer protocols to maintain clocking. SONET interfaces support two levels of scrambling, as follows:

  • SONET frame scrambling mode required by the International Telecommunications Union Telecommunication Standardization (ITU-T) GR-253 standard. This mode uses a 1 + x6 + x7 algorithm to scramble the section overhead of the SONET frame. It does not scramble the first row of the section overhead.

  • Cell payload scrambling is optional and is defined in ITU-T I.432, section 4.5.3. This mode randomizes the bits in the payload portion of an ATM cell to make sure that the beginning of each new cell is recognized. It leaves the 5-byte header unscrambled.

Synchronous Transport System (STS) stream scrambling must be enabled on every SONET device and is the default for SONET interfaces.

Cell payload scrambling or SONET High-level Data Link Control (HDLC) scrambling can be enabled or disabled, and on Juniper routers is enabled by default to provide better link stability. Both sides of a connection must either use scrambling or not use it.


HDLC payload scrambling conflicts with traffic shaping configured using leaky bucket properties. If you configure leaky bucket properties, you must disable payload scrambling because the software rejects configurations that have both features enabled. For more information, see Junos OS Network Interfaces Library for Routing Devices.

On a Channelized OC12 interface, the SONET payload-scrambler statement is ignored. To configure scrambling on the DS3 channels on the interface, include the t3-options payload-scrambler statement in the configuration for each DS3 channel.

  1. Checking SONET HDLC Payload Scrambling

  2. Configuring SONET HDLC Payload Scrambling

Checking SONET HDLC Payload Scrambling


If you find that payload scrambling is not enabled, you might want to enable or configure it because it provides better link stability when it is working.


In the Junos OS command-line interface (CLI) operational mode, you can use one of the following two commands to check for SONET HDLC control payload scrambling:


Sample Output 1

user@host> show configuration interfaces so-0/0/0

Sample Output 2

user@host> show configuration interfaces so-0/0/0

Sample Output 3

user@host> show interfaces so-0/0/1


Sample output 1 shows that the SONET interface payload scrambling has been enabled.

Sample output 2 shows that HDLC payload scrambling has been disabled. If you use the show configuration or show configuration interfaces command, you must scroll to the particular interface for payload scrambling status.

Sample output 3 shows that payload scrambling has been disabled. To explicitly configure payload scrambling, see Configuring SONET HDLC Payload Scrambling.

Configuring SONET HDLC Payload Scrambling


You might want to configure SONET HDLC payload scrambling (which is the configurable cell payload scrambling mentioned earlier) if it has been disabled. Configuring payload scrambling provides better link stability.


Payload scrambling is the default for Juniper Networks routers. To return to the default, that is, to re-enable payload scrambling, delete the no-payload-scrambler statement from the configuration.


To explicitly configure HDLC payload scrambling, follow these steps:

  1. In configuration mode, go to the following hierarchy level.

  2. Configure payload scrambling.

  3. Verify the configuration.

  4. Commit the configuration.