Difference Between SONET and SDH
Last Updated : 07 Feb, 2025
SONET (Synchronous Optical Network) and SDH (Synchronous
Digital Hierarchy) are two complex systems often used interchangeably;
they describe the transmission of digital signals over fiber optics. Both are
universally implemented in telecommunications for offering high-speed,
high-capacity data transmission, although, they possess some regional
and technical discrepancies. SONET is used in the North American region
while the international similar technology is known as SDH and is mainly
used in Europe and other parts of the globe. By identifying differences
between SONET and SDH it is easier to decide which technology is best
suited for the organization’s network technology.
Synchronous Optical Network (SONET)
SONET stands for Synchronous Optical Network. It is a communication
protocol, developed by Bellcore which is used to transmit a large amount
of data over relatively larger distances by using optical fiber. By SONET,
multiple digital data streams are transferred over optical fibers at the
same time.
Advantages of SONET
High Data Capacity: SONET is suitable for the large-scale
telecommunications networks owing to its ability to transmit large
volumes of data.
Efficient Synchronization: It enables an excellent synchronization
of several parallel digital data streams utilizing the common clock,
thus minimizing the timing problems.
Fault Management: SONET also supports high end options of error
detection and recovery built-in so that network down time can easily
be avoided.
Interoperability: As such SONET systems are compatible with the
earlier laid down networks and this is advantageous as newer
technology can be implemented without having to redo the whole
network.
Disadvantages of SONET
Region-specific: SONET is mainly present in North America only
which is a disadvantage when it comes to global integration.
Complex Equipment: In general, implementation of SONET
infrastructure involves appropriate and very costly equipment.
Costly Upgrades: With advent of newer technologies depending
upon higher speeds, the upgrading of SONET networks can be
burdensome in terms of both of time and money.
Synchronous Digital Hierarchy (SDH)
SDH stands for Synchronous Digital Hierarchy and is defined as a
multiplex technology used in telecommunications. Synchronous Optical
Network (SONET) is primarily used in North America, while SDH is
internationally adopted. Although they are similar, SDH is not directly
compatible with SONET but shares common features, especially in terms
of high-order multiplexing. These technologies offer faster and more cost-
effective network interconnection compared to Plesiochronous Digital
Hierarchy (PDH).
Advantages of SDH
Global Standard: SDH is implemented in most of Europe’s as well
as some parts of Asia and other parts of the world where fiber optic
communication is standard.
Flexible Data Rates: SDH has the ability of providing various
options for the rates transmission enables it to be implemented in
different networks from small networks to the large ones.
Improved Network Management: SDH also has some advanced
features such as efficient network management tools for easier
monitoring of networks and solving of related problems.
Supports Various Data Types: Telecommunication networks can
support multiple kinds of traffic including voice, video and IP across
the same network.
Disadvantages of SDH
Higher Complexity: SDH systems are complex and this may lead
to more time to install the systems yet, they require professional
staff to manage them.
Interoperability Issues with SONET: SDH and SONET are
conceptually similar but they are not interoperable, and hence when
two different SDH or SONET networks are planned across different
regions they need conversion interfaces.
Initial Setup Costs: This remains true despite the fact that there
are likely to be high costs in the initial investment of SDH
infrastructure because of specialized equipment and stiff network
planning.
Difference Between SONET and SDH
SONET SDH
SONET stands for Synchronous SDH stands for Synchronous
Optical Network. Digital Hierarchy.
It is a network node interface,
It is a digital hierarchy interface user-network interface and U
for the optical transmission. reference-point interface to assist
BISDN.
It is developed by ITU-T
It is developed by ANSI (American (International Telecommunication
National Standards Institute). Union – Telecommunication
Standardization Sector).
It has total number of transport It has total number of transport
SONET SDH
overhead of 9×3 = 27 bytes. overhead of 9×9 = 81 bytes.
It can transmit in both
It can transmit data in only
synchronous mode and
synchronous mode.
asynchronous mode.
It does not provides better
It provides better transmission
transmission rates as compared
rates as compared to SONET.
to SDH.
Optical Carrier level-1(OC-1) is the
fundamental unit of SONET. This
unit serves as the basis for other
rates which are as follows-
OC-3
