Pdh vs sdh describes difference between pdh and sdh

SONET/SDH vs DWDM: Which Is Better?

The main differences between sdh and dwdm are listed below:

Item	SONET/SDH	DWDM
Number of topological structures to carry the same traffic	more	less
Cost	relatively lower	relatively higher
Application scenario	Perfect choice when the design requires under 4-10 OC-192 rings, usually for the past network structure	Perfect choice when the design requires over 10 OC-192 rings, better for the future network building
Number of optical fibers required	more	less

The need of SONET granularity is due to the presence of low-speed service demands for example DS1/DS3 and the insufficient sub-wavelength grooming within the DWDM platforms. DWDM has a goal to carry the same traffic in as few topological structures (e.g, rings) as possible. DWDM does this at the expense of allowing some visitors to traverse longer distances than it does in SONET. For any simple example, the very best SONET design may generate a bunch of topologically different OC-48 and OC-192 rings, while the most economic DWDM transport network may consist of just a single DWDM ring.

Traditionally Internet traffic runs on IP which rides on ATM and SONET/SDH or IP over SDH then to an optical layer (as shown in the figure below). The misconception that IP rides on ATM/SDH is the fact that IP traffic is small and needs to be combined with other services for cost-effective delivery. Unlike this delusion, the concept of IP over DWDM supports voice, video and data traffic and dedicates the remainder to high-speed data traffic. Elimination of layers (SONET/ATM) will ease the task of network management and will be cost effective.

Figure 1: Internet Traffic on SONET/SDH and DWDM