Hereby I would like to share (learn) you guys some basic principles or technologies which
are or were used to be implemented on Fiber Optic Networks.
These are the most common, and are based in Layer 1 + 2 of the OSI-Model.


There are two TDM transmission systems with their hierarchy in use: "plesiochronous (nearly synchronous) digital hierarchy (PDH)" and "synchronous digital hierarchy (SDH)", the most recent one providing higher speed channels like DWDM.


This hierarchy was developed nearly 40 years ago to carry digital voice channels. It structures the transmission infrastructure into several layers. Different hierarchical levels are used in North America, in Europe and in Japan

See Attach for Table...

PDH is an asynchronous multiplexing scheme in the sense that the different tributary channels don't have to be clock synchronized between them and with the aggregate channel. A centralized and very stable network clock is unnecessary avoiding the problems of clock stability, recovery and distribution.
But the consequence is the implementation complexity of cross connecting the aggregated channels, with demultiplexing and remultiplexing at each cross connect node.


There are two standards for the synchronous digital hierarchy: SONET (Synchronous Optical NETwork) for North America and SDH (Synchronous Digital Hierarchy): the ITU international standard.
The two Key benefits of this new hierarchy versus PDH are:
Higher transmission and aggregate rates
Direct multiplexing and cross connecting without intermediate multiplexing stages, due to its synchronous nature and pointers in multiplex streams that delineate the aggregated sub streams.
The SONET or SDU transmission system is structured in several levels, each of them characterized by a transport channel called the Synchronous Transport Signal (STS) in SONET, the Synchronous Transport Module (STM) in SDH.
This channel is transmitted over an Optical Carrier (OC).
The different possible SONET /SDH levels are presented in the following table:

See Attach for Table

Note that the Bit rate of STS-N (Level N) = N* STS-1 = N* 51.84 Mbps and STM-N = 3*STS-N.
The predominant used channels are the STM-1 (or STS-3) and the STM-4 (or STS-12).
It is a superhighway using fiber optics that rings most major cities and provides terabits worth of bandwidth. It is the basic foundation, the underlying transmission network of very high-speed networks such as ATM or SMDS, but also of terrestrial Video networks.
The STS or STM transport channel aggregates lower speed channels (e.g. 4 STM-1 into 1 STM 4) and also multiplexes T1 or E1, T3 or E3. The aggregated streams are called Virtual Tributaries (in SONET), Virtual Containers (in SDH).
There are also different levels of tributary channels as listed in the next table.

See attach for table...

DWDM ( Dense Wavelength Division Multiplexing )

The most recent is DWDM : Dense Wavelength Division Multiplexing, however I briefly explained this one in my first Tutorial on Fiber Optic Networks. You can find this one here :

Hope you enjoyed it,


I just saw that the tables are f**ked up by posting. These are the Bandwith overviews.
I will make mew tables and post them later. Sorry for the incovenience.


Now I've put the tables in an attach, as a referral...
Sorry for the possible confusion...