SDH vs PDH | Difference between PDH and SDH

What is SDH and PDH? What’s the difference between SDH and PDH? SDH vs PDH are two different synchronous transmission methods. By reading this article, you can learn as below :

What is SDH?

What is PDH?

SDH and PDH difference;

SDH vs PDH -How to Choose?

SDH and PDH ’s Alternative

More types of SDH and PDH product click here.

Part I.What is SDH and PDH?

What is SDH ?

SDH called Synchronous Digital Hierarchy, is a synchronous transmission technology based on optical fiber communication system. SDH is a synchronous TDM technology that multiplexes low-order signals into high-order signals. Because the entire network is synchronized, users can easily embed and extract individual bit streams within the data stream. SDH is also a multiplexing technology. It provides fast network interconnection, combining low bit data streams with high bit data streams. The multiplexing feature of SDH is reflected in its ability to multiplex 63 channels of 2.048Mbps E1 signals into the 155.52Mbps signal STM-1.

SDH work diagram SDH vs PDH

Signals from other systems serve as payloads and are packaged into appropriate STM-N signals for transmission in the SDH network. Go to the other end to unpack, take out the payload, and restore the original signal.

SDH Multiplexing SDH vs PDH

SDH Multiplexing Demonstration

What is PDH?

PDH called Parallel Data Highway, is a quasi-synchronous transmission technology based on digital transmission. PDH is a synchronous TDM technology that multiplexes different data streams into a single signal. PDH defines multiple multiplexing levels, such as 2Mbps (E1), 8Mbps (E1) and 34Mbps (E4). The multiplexing feature of PDH is reflected in that it can multiplex 30 64Kbps channels into the 2.048Mbps signal E1.

SDH vs PDH PDH application

PDH application

Part II.SDH vs PDH : What difference and How to Choose

SDH vs PDH – Key difference

Max Capacity64G34M
Max rate40Gbps566Mbps
Min rate155.52Mbps1.544Mbps
InterfaceStandard optical interfaceRegional electrical interface
NetworkChain and RingPoint to Point

1.Capacity and Speed

The maximum capacity of SDH is 64G.

The maximum capacity of PDH is 34M.

The biggest difference between SDH and PDH is the different transmission rates.

The maximum rate of PDH is 566Mbps, and the minimum rate is 1.544Mbps.

The maximum rate of SDH is 40Gbps and the minimum rate is 155.52Mbps.


The implementation cost and transmission cost of SDH are relatively high.

The implementation cost and transmission cost of PDH are relatively low.


Interface is also the SDH vs PDH difference.

SDH uses standard optical interfaces to enable different brand devices to communicate with each other. This ensures uniformity of digital signal and frame structure standards. Baudcom SDH terminal and ADM devices can work smoothly with other brands SDH device, like Huawei, ZTE, Nokia etc.

PDH uses regional electrical interface specifications and lacks a unified global standard. This causes problems in the interconnection of PDH equipment in different regions. The PDH devices belong to different brands can not work together. For example, Baudcom PDH fiber multiplexer can not work other brands’ PDH device.

4.Transfer method

SDH adopts synchronous transmission mode and has high transmission rate and stability.

PDH adopts quasi-synchronous transmission mode, and the transmission rate is relatively low.

5.Network method

Network is also the SDH vs PDH difference.
SDH supports chain and ring network and point to point application, and has high flexibility and protection functions. This can quickly restore services in the event of a failure.

63E1 STM-1 multiplexer point to point application

E1 STM-1 multiplexer point to point application

63E1 STM-1 ADD-DROP SDH Multiplexer application

STM-1 ADD-DROP SDH Multiplexer application

SDH optical terminal Chain Network Application

SDH optical terminal Chain Network Application

PDH only supports point-to-point networking, has poor flexibility, and lacks similar protection mechanisms.

16E1 PDH Fiber multiplexer p2p application

16E1 PDH Fiber multiplexer p2p application

6.Maintenance method

SDH uses network management functions to monitor and configure network resources in real time. It enables efficient and stable operation of the network.

There are fewer overhead bytes for operation and maintenance in the PDH frame structure, which limits the efficiency and flexibility of its operation and maintenance to a certain extent.

SDH vs PDH – How to Choose?

SDH has higher transmission rate and reliability and is suitable for high-speed and long-distance transmission scenarios. If the cost is acceptable, the SDH is best choice.
PDH has low transmission cost and good compatibility, and is suitable for short-to-medium distance and low-speed transmission scenarios.

Part III.SDH vs PDH:Alternative

SDH vs PDH – Alternative

There are many alternatives to SDH and PDH, such as wavelength division multiplexing (WDM), EoS and PoS, etc.Among them, Eos and Pos can improve the compatibility and scalability of the network.Eos and Pos are methods of transmitting Ethernet and IP packets over pdh sdh network. They can support different service levels and quality of service.


Although the transmission rate of SDH is faster than that of PDH, and the capacity of transmitting data is larger than that of PDH. But the implementation cost and transmission cost of SDH are higher than that of PDH. So it’s not that SDH is necessarily better than PDH, it depends on your needs.

Post time:2024-04-21


Lomoveishiy – Finland

I needed those to connect my PC on the third floor to have internet access in that room, and ISP installed their modem on the first floor only. After dropping fiber patch cables, plugged in all cables into these media converters at both sides, and link came up instantly. Was much easier than I thought!

Raymond – USA

Great experience – units worked straight out of the box – just needed plug in cables and we were done. I also like the possibility to enable jumbo frames, while we do not have a need for this feature at the current moment it’s great to have this option.

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