Tag Archive: TDM


Continued… DWDM Part VIII

As mentioned in last post,  today I’ll share again on the “highway analogy” but using different diagram, which I believe is more appealing for clearer understanding on TDM-DWDM relationship.

Consider a highway analogy where one fiber can be thought of as a multilane highway. Traditional TDM systems use a single lane of this highway and increase capacity by moving faster on this single lane. In optical networking, utilizing DWDM is analogous to accessing the unused lanes on the highway (increasing the number of wavelengths on the embedded fiber base) to gain access to an incredible amount of untapped capacity in the fiber. An additional benefit of optical networking is that the highway is blind to the type of traffic that travels on it. Consequently, the vehicles on the highway can carry ATM packets, SONET, and IP.

By beginning with DWDM, service providers can establish a grow-as-you-go infrastructure, which allows them to add current and next-generation TDM systems for virtually endless capacity expansion as shown in the following diagram that illustrates the capacity expansion potential of DWDM.

Capacity Expansion Evolution

Capacity Expansion Evolution

DWDM also gives service providers the flexibility to expand capacity in any portion of their networks – an advantage no other technology can offer. Carriers can address specific problem areas that are congested because of high capacity demands. This is especially helpful where multiple rings intersect between two nodes, resulting in fiber exhaust.

Service providers searching for new and creative ways to generate revenue while fully meeting the varying needs of their customers can benefit from a DWDM infrastructure as well. By partitioning and maintaining different dedicated wavelengths for different customers, for example, service providers can lease individual wavelengths-as opposed to an entire fiber-to their high-use business customers.

Compared with repeater-based applications, a DWDM infrastructure also increases the distances between network elements-a huge benefit for long-distance service providers looking to reduce their initial network investments significantly. The fiber-optic amplifier component of the DWDM system enables a service provider to save costs by taking in and amplifying optical signals without converting them to electrical signals. Moreover, DWDM allows service providers to do it on a broad range of wavelengths in the 1.55-µm region. For example, with a DWDM system multiplexing up to 16 wavelengths on a single fiber, carriers can decrease the number of amplifiers by a factor of 16 at each regenerator site. Using fewer regenerators in long-distance networks results in fewer interruptions and improved efficiency.

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

To be continued… DWDM Part IX

Share

Continued… DWDM Part VII

Yesterday, I shared on 2 options for the service providers to provide an economical solution in resolving fiberoptic capacity crisis.  Today, I’ll further share on the 3rd option, DWDM.

Option #3

The third choice for service providers is dense wavelength division multiplexing (DWDM), which increases the capacity of embedded fiber by first assigning incoming optical signals to specific frequencies (wavelength, lambda) within a designated frequency band and then multiplexing the resulting signals out onto one fiber. Because incoming signals are never terminated in the optical layer, the interface can be bit-rate and format independent, allowing the service provider to integrate the DWDM technology easily with existing equipment in the network while gaining access to the untapped capacity in the embedded fiber.

DWDM combines multiple optical signals so that they can be amplified as a group and transported over a single fiber to increase capacity as shown in the following diagram.

Increased Network Capacity - WDM

Increased Network Capacity - WDM

As shown above and still referring to the highway analogy, DWDM, on the other hand, relates to the accessing the unused lanes on the highway. Another way to increase auto throughput is to add more lanes that is equivalent to wavelength multiplexing. Eeach signal carried can be at a different rate (OC-3, OC-12, OC-24, etc.) and in a different format (SONET, ATM, data, etc.) For example, a DWDM network with a mix of SONET signals operating at OC–48 (2.5 Gbps) and OC–192 (10 Gbps) over a DWDM infrastructure can achieve capacities of over 40 Gbps. A system with DWDM can achieve all this gracefully while maintaining the same degree of system performance, reliability, and robustness as current transport systems – or even surpassing it.  Future DWDM terminals will carry up to 80 wavelengths of OC–48, a total of 200 Gbps, or up to 40 wavelengths of OC–192, a total of 400 Gbps—which is enough capacity to transmit 90,000 volumes of an encyclopedia in one second. Wow!

How is this possible?

The technology that allows this high-speed, high-volume transmission is in the optical amplifier. Optical amplifiers operate in a specific band of the frequency spectrum and are optimized for operation with existing fiber, making it possible to boost lightwave signals and thereby extend their reach without converting them back to electrical form. Demonstrations have been made of ultrawideband optical-fiber amplifiers that can boost lightwave signals carrying over 100 channels (or wavelengths) of light. A network using such an amplifier could easily handle a terabit of information. At that rate, it would be possible to transmit all the world’s TV channels at once or about half a million movies at the same time.  Wow! Wow!

In next post, I’ll share again on the “highway analogy” but using different diagram that I believe is more appealing for clearer understanding on TDM-DWDM relationship.

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

To be continued… DWDM Part VIII

Share

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

Share

Continued… DWDM Part IV

To recap, DWDM technology has been developed to increase the capacity of a single fiber SONET/SDH technology, which transmits information via a single channel or wavelength of light via each fiber optic strand. The term “dense” refers to high-wavelength or high-channel count per fiber. In essence, each wavelength represents a different transmission channel and can transmit data at 10 Gbps.

DWDM can offer potentially unlimited bandwidth at multi-gigabit and multi-terra-bit rates by carrying multiple light waves of different frequencies on a single fiber. A single fiber can carry up to 128 wavelengths and researchers/technologists are working on DWDM technologies that could carry more than 1,000 channels within a single fiber.

Operationally, optical network deployments represent a significant CAPEX (Capital Expenditures) investment. However, the rapidly falling cost of raw fiber will accelerate the adoption of this technology.

For today post, I’ll discuss on the capabilities and merits of DWDM as practical considerations for the service providers to deploy DWDM networks.

  • Extendibles:

DWDM is a more cost-effective alternative to SONET/SDH, which employs Time Division Multiplexing (TDM). 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 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.

DWDM, on the other hand, relates to the accessing the unused lanes on the highway. Another way to increase auto throughput is to add more lanes that is equivalent to wavelength multiplexing.  DWDM combines multiple optical signals so that they can be amplified as a group and transported over a single fiber to increase capacity. Each signal transmitted can be at a different rate (OC–3/12/24, etc.) and in a different format (SONET/SDH, ATM, IP, WDM, and Gigabit Ethernet, etc.).

[I’ll discuss further on TDM-DWDM analogy with graphical illustrations in future post for a better understanding]

The operations associated with TDM electronic-to-optical and optical-to-electronic somehow rather slow the performance of SONET/SDH networks. These operations convert data signals from the electronic network to optical format, route the signals to their proper destinations within the optical part of the infrastructure, and then convert them back again for their continued journey over the electronic portion of the network.

DWDM technology, on the other hand, employs an Erbium Doped Fiber Optic Amplifier (EDFA) with advanced filtering techniques to amplify optical signals without converting them to electrical signals.DWDM uses Optical Bi-directional Line Switched Ring (OBLSR) topologies to optimize bandwidth capacity of the in-place fiber optic plant and the traffic volumes transported via the Optical Layer. A DWDM infrastructure also increases the distances between network elements – a big benefit for long-distance (long-haul) service providers looking to reduce their initial network investments significantly.

DWDM uses advanced wavelength routing protocols and gigabit routers for provisioning of wavelength or channel capacity. DWDM employs tunable lasers for enabling development of multiple, independent, narrowly spaced transmission channels or wavelengths on a single fiber optic strand.

Source:  DWDM: Technologies and Initiatives by Khoa Duc Tran

To be continued… DWDM Part V – Capabilities and Merits

Share
1 visitors online now
0 guests, 1 bots, 0 members
Max visitors today: 2 at 01:10 am +08
This month: 17 at 12-09-2017 09:54 am +08
This year: 20 at 02-01-2017 05:29 am +08
All time: 177 at 01-10-2011 08:28 pm +08