# Configuring the QoS Shaping Mode for ATM Interfaces

In frame mode, SAR shaping is controlled by the ATM application. Shaping is based on the number of bytes in the frame, without regard to cell encapsulation or padding overhead; this is the default mode.

In cell mode, SAR shaping is controlled by the QoS application. Shaping is based on the number of bytes in cells, and accounts for the ATM cell encapsulation and padding overhead.

To configure the operational shaping mode for ATM interfaces:

1. Configure the ATM interface.
   host1(config)#interface atm 5/1

   | Note: For ATM interfaces on ERX7xx models, ERX14xx models, and the ERX310 router, you must use port 0.

2. Configure the shaping mode and specify either frame or cell.
   host1(config-if)#qos-shaping-mode cell

   | Best Practice: We recommend that you clear the statistics counters whenever you change the QoS shaping mode. Otherwise, the statistics contain a mixture of frame-based and cell-based values.

#### Related Documentation

- Per-Packet Queuing on the SAR Scheduler Overview
- interface atm
- qos-mode-port
- qos-shaping-mode