Point-to-Multipoint DWDM raises optical reach

Point-to-Point dense wave division multiplexing is a technology that lets service providers transmit more than one lambda, or wavelength, between two locations.

Given the enormous capacity multiple wavelengths provide, in most applications the two locations connected by Point-to-Point DWDM are typically central offices or large, multitenant office buildings that generate and consume large amounts of bandwidth.

Taking the concept of Point-to-Point DWDM to a new level is Point-to-Multipoint DWDM, which differs in the number of endpoints that receive the traffic.

In metropolitan areas, DWDM initially provided carriers with the ability to significantly increase the capacity of fiber strands, thereby providing favorable economics.

However, the downside to the technology is that a positive return on investment is achieved only when it serves the largest enterprise customers that generate significant recurring monthly revenue streams.

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That ignores 90% of enterprise customers, however. The emergence of Passive Optical Networking (PON) makes it possible for carriers to deploy wavelength, multiwavelength and fractional wavelength services to enterprise customers over the same fiber infrastructure.

Now carriers can use one infrastructure to serve all their customers - large and small - while easily scaling to provide higher service levels as more customers embrace value-added services such as storage-area networks (SAN) and virtual LANs.

The components of Lamda-PON

Point-to-Multipoint DWDM based on PON consists of these elements:

A DWDM switch collocated with an Optical Access Switch (OAS) in the central office.

An Optical Transponder or Intelligent Optical Terminals (depending on the rate of service) on the customer premises.

A PON between the central office and the customer premises.

Among the key elements of a PON are the passive couplers and splitters deployed in the outside plant that combine or split the laser signal at each junction point. Because these splitters and couplers are fiber, once the carrier installs the outside plant network, all changes and upgrades occur only at the endpoints. This eliminates the need and expense of making changes to the outside plant.

The collocation of the DWDM switch and the optical access switch in the central office allows the transmission of fractional and dedicated wavelength services over the same PON. For customers requiring a dedicated wavelength, the DWDM switch transmits wavelengths through the OAS and onto the PON at a frequency predetermined for each end customer. While this traffic travels through every splitter and coupler, and reaches all endpoints, each optical transponder is outfitted with a filter that only receives the signal that is intended for it, ensuring that data is secure and that each customer is receiving the correct service level.

For customers receiving fractional wavelength offerings, service is originated and aggregated at the optical access switch in the central office, without involving the DWDM switch.

The traffic then travels at a maximum speed of 622M bit/sec downstream along the PON and is terminated at each customer location by optical terminals equipped with T-1 and Ethernet interfaces.

Enterprise customers receiving fractional wavelength services have the option of choosing between 10M and 100M bit/sec of service.

When demand surpasses 100M bit/sec, companies can upgrade to a dedicated wavelength offering (2.5G bit/sec) without changes to the outside plant or service disruptions.

The ability to operate a single, future-proof fiber infrastructure capable of serving all types of enterprise users brings with it a tremendous opportunity for carriers and corporations. As a result of the precision of today's optics, a single PON can support multiple traffic types and data rates to serve businesses of all sizes, minimizing carriers' operational and capital expenditures.

For companies, the economical Point-to-Multipoint DWDM services that PON enables bring with them a new breed of applications such as SANs and VLANs.

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Point-to-Multipoint DWDM raises optical reach

The components of Lamda-PON

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