PDH offers a fixed hierarchy of bit rates, which range from 1. 544 Mbps for T1 lines to 45 Mbps for T3 lines. For example, an OC-48 SONET circuit operates at approximately 2. This section of the SDH/SONET tutorial explains PDH concepts and the various PDH rates, including 2Mbps, 8Mbps, 34Mbps, and 140 Mbps. This encapsulation allows. Synchronous Optical Networking (SONET) and Synchronous Digital Hierarchy (SDH) are standardized protocols that transfer multiple digital bit streams synchronously over optical fiber using lasers or highly coherent light from light-emitting diodes (LEDs). The maximum capacity is about 566 Mbps. However, bit−rate is not exact multiple of lower speed: 2048 −> 8448 −> 34368 −> 139264.