Tag Archive: SDH

Continued… DWDM Part XI

It’s nice to be back online again after a long Eid ul-Fitr break and quite busy at the office.

Frost & Sullivan published its Market Insight on “WDM PON: How Long Is It Going To Take?” on 16 Nov 2009 and the extract of the report was posted in the previous post (DWDM Part X), among others stated that “…. The idea is right with WDM-PON but the technology still needs 4-5 years to become practical. ….”. Thus, Adeel Najam (the author) anticipated that WDM-PON will become practical in 2013-2014.

In Malaysia, deployment of DWDM has taken place. Thanks to the bold Telcos/Carriers such as Fiberail and TIME dotCom.

TIME dotCom has a fiber optic network that covers a large portion of Malaysia and features 5 redundant routes totaling 6,000 kilometers. Upgrading from SDH to DWDM in 2009 gives TIME dotCom a new competitive edge and increased market share.

The new DWDM network has been operational  since December 2009 and TIME dotCom decided to make the move to DWDM because their concentration is in the wholesale market where the customers now want more bandwidth, and they needed to have a very effective network that could provide 99.999% reliability. SDH networks on the other hand are subject to congestion and did not provide the efficiencies the company wanted for its customers.

The maximum connection speed that the SDH network could support was 10 Gbps. TIME’s new DWDM network can support as many as 88 wavelengths per fiber, with each wavelength providing 10 Gbps connectivity. And in the future, the DWDM system can be easily upgraded to support 40 Gbps or even higher data rates per wavelength.

TIME’s DWDM network with 88 wavelengths per fiber where the capacity is virtually unlimited plus the GMPLS-based mesh protection at the wavelength level that offers automatic reroute protection even in the event of multiple fiber cuts. This scheme enables the TIME to offer 99.999% reliability that it can provide using its 5 fiber routes and therefore, gives TIME an important differentiator.

The DWDM network provides substantially higher bandwidth with fewer network elements and should be less expensive to operate, particularly when costs are calculated on a per-bit basis and the carrier can expect a significant OPEX reduction.

With new DWDM+GMPLS-based mesh protection, TIME’s Cross Peninsular Cable System (CPCS) network is claimed to be the most robust transborder terrestrial system ever built. Designed as a fully meshed network over 5 diverse fiber routes running along both
coasts, alongside major highways and via utility corridors, CPCS traverses more than 6,000 km with dedicated fiber optics connecting Thailand and Singapore.

Below is TIME’s DWDM network diagram:

TIME dotCom's DWDM Network

TIME dotCom's DWDM Network

Source:  Tellabs Insight Magazine, 3rd Quarter 2010. Click  here to download.

Tellabs Insight Magazine, 3rd Quarter 2010

Tellabs Insight Magazine, 3rd Quarter 2010


GMPLS:  Generalized Multi Protocol Label Switching

OPEX:  Operating Expenses/Expenditures

PON:  Passive Optical Network

SDH:  Synchronous Digital Hierarchy

WDM:  Wavelength Division Multiplexing

To be continued… DWDM Part XII


Continued… DWDM Part VI

For today’s post (Part VI) and next post (Part VII), I”ll share on the options to resolve fiberoptic capacity challenges that include graphical illustration on TDM-DWDM analogy for a better understanding as promised in DWDM Part IV post.

At present, I believe many carriers are nearing 100% capacity utilization across significant portions of of their networks. Another problem for carriers is the challenge of deploying and integrating diverse technologies in one physical infrastructure. Customer demands and competitive pressures mandate that carriers offer diverse services economically and deploy them over the embedded network. DWDM provides service providers an answer to that demand. As mentioned previously, use of DWDM allows service providers to offer services such as e-mail, video, and multimedia carried as Internet protocol (IP) data over asynchronous transfer mode (ATM) and voice carried over SONET/SDH. Despite the fact that these formats—IP, ATM, and SONET/SDH—provide unique bandwidth management capabilities, all three can be transported over the optical layer using DWDM. This unifying capability allows the service provider the flexibility to respond to customer demands over one network.

A platform that is able to unify and interface with these technologies and position the carrier with the ability to integrate current and next-generation technologies is critical for a carrier’s success.

Resolving the Capacity Crisis

Faced with the multifaceted challenges of increased service needs, fiber exhaust, and layered bandwidth management, service providers need options to provide an economical solution as follows:

Option #1

One way to alleviate fiber exhaust is to lay more fiber,  and, for those networks where the cost of laying new fiber is minimal, this will prove the most economical solution. However, laying new fiber will not necessarily enable the service provider to provide new services or utilize the bandwidth management capability of a unifying optical layer.

Option #2

A second option is to increase the bit rate using time division multiplexing (TDM), where TDM increases the capacity of a fiber by slicing time into smaller intervals so that more bits (data) can be transmitted per second as shown in the following diagram.

TDM Increased Network Capacity

TDM Increased Network Capacity

The figure above is a highway analogy, where one fiber can be considered as a multi-lane highway, can be used to explain the difference between the two (TDM and DWDM). TDM relates to traffic flow on single lane of the highway. To increase the throughput of autos, one can increase their speed that is equivalent to time multiplexing.

Traditionally, this has been the industry method of choice (DS-1, DS-2, DS-3, etc.). However, when service providers use this approach exclusively, they must make the leap to the higher bit rate in one jump, having purchased more capacity than they initially need. Based on the SONET hierarchy, the next incremental step from 10 Gbps TDM is 40 Gbps—a quantum leap that many believe will be a big challenge (if not be possible) for TDM technology in the near future. This method has also been used with transport networks that are based on either the synchronous* optical network (SONET) standard for North America or the synchronous* digital network (SDH) standard for international networks.

The telecommunications industry adopted the SONET or SDH standard to provide a standard synchronous* optical hierarchy with sufficient flexibility to accommodate current and future digital signals. SONET or SDH accomplishes this by defining standard rates and formats and optical interfaces. For example, multiple electrical and optical signals are brought into a SONET terminal where they are terminated and multiplexed electrically before becoming part of the payload of an STS–1, the building block frame structure of the SONET hierarchy.  The STS–1 payloads are then multiplexed to be sent out on the single fiber at a single rate: OC–3 to OC–12 to OC–48 and eventually to OC–192. SDH has a similar structure with STM-n building block resulting in signal rates of STS–1 through STM–64.

SONET and SDH, two closely related standards, provided the foundation to transform the transport networks as we know them today. They govern interface parameters; rates, formats, and multiplexing methods; and operations, administration, maintenance, and provisioning (OAM&P) for high-speed transmission of bits of information in flashing laser-light streams.

*Note: A synchronous mode of transmission means that the laser signals flowing through a fiber-optic system have been synchronized to an external clock. The resulting benefit is that data streams transmitting voice, data, and images through the fiber system flow in a steady, regulated manner so that each stream of light can readily be identified and easily extracted for delivery or routing.

Source: Dense Wavelength Division Multiplexing (DWDM)  by The International Engineering Consortium (IEC)

To be continued… DWDM Part VII


My apology for being “off mode” for 2 weeks since my last post on July 22. Last week Fri-Sun, my colleagues and I attended our company’s corporate team building event at Jeram Besu, Pahang (Malaysia). It was an enjoyable event with the main activities of white water rafting and 4WD off-road to Jerembun waterfall (not forget to mention that we indulged ourselves with eating durian, king of fruits).

I was also quite busy lately as I was on DWDM assignment. I take this opportunity to explore DWDM and would like to share the info on this blog. This new topic and other future topics on interesting technology or solution will be posted under the new category of “Next Generation Network (NGN)“.

What on earth is DWDM?

DWDM is a short or an acronym for Dense Wavelength Division Multiplexing. DWDM is a fiber-optic transmission technique. It involves the process of multiplexing many different wavelength signals onto a single fiber. So each fiber have a set of parallel optical channels each using slightly different light wavelengths. It employs light wavelengths to transmit data parallel-by-bit or serial-by-character.

In short, DWDM is a technology that uses fiber-optics transmission techniques that employ light wavelengths to transmit data as shown below.
How DWDM works

How DWDM works

Figure above shows a diagram that depicts how DWDM works.  As shown, four incoming sources are:
1. Multiplexed onto one single fiber
2. Transmitted
3. Demultiplexed onto four outgoing fibers (incoming signals are retrieved)

What so special about DWDM?

DWDM is a very crucial component of optical networks that will allow the transmission of data: voice, video-IP, ATM and SONET/SDH respectively, over the optical layer.

This allows service providers to offer the following Triple Play services as IP data over ATM or voice over SONET (or SDH):

  • Video
  • Multimedia
  • E-mail
Development of DWDM Technology
Let’s backtrack a little bit to explore the history of Wavelength Division Multiplexing (WDM) development. Early WDM began in the late 1980s using the two widely spaced wavelengths in the 1310 nm and 1550 nm (or 850 nm and 1310 nm) regions, sometimes called wideband WDM. Figure below shows an example of this simple form of WDM. Notice that one of the fiber pair is used to transmit and one is used to receive. This is the most efficient arrangement and the one most found in DWDM systems.
Example of simple form of WDM with 2 channels

Example of simple form of WDM with 2 channels


  • DWDM: Dense Wavelength Division Multiplexing
  • WDM: Wavelength Division Multiplexing
  • NGN: Next Generation Network
  • ATM: Asynchronous transfer mode
  • SONET: Synchronous data transmission on optical media (American National Standards)
  • SDH: Synchronous Digital Hierarchy (international equivalent of SONET)
  • IP: Internet Protocol

Dense Wavelength Division Multiplexing (DWDM) by Luc Pelletier & Miguel Pinard
Introduction to DWDM for Metropolitan Networks

To be continued… DWDM Part II

1 visitors online now
0 guests, 1 bots, 0 members
Max visitors today: 4 at 12:43 am +08
This month: 16 at 10-04-2017 12:59 am +08
This year: 20 at 02-01-2017 05:29 am +08
All time: 177 at 01-10-2011 08:28 pm +08