What is WDM-PON?

01 January 2009 |


Wavelength Division Multiplexing-Passive Optical Network (WDM-PON) is an access network technology that has the potential to significantly alter carrier infrastructures.

It creates a wavelength-based logical point-to-point architecture upon a physical point-to-multipoint fibre topology. WDM-PON is a simple concept that has the potential to become the unified access and backhaul technology of the future, carrying data from residential, business and carrier wholesale services on a single platform. Its long-reach capability and bandwidth scalability enables carriers to serve more customers from fewer active sites without compromising security and availability.

WDM-PON uses WDM multiplexing/demultiplexing technology to ensure that data signals can be divided into individual outgoing signals that are connected to buildings or homes. This hardware-based traffic separation provides customers with the benefits of a secure and scalable point-to-point wavelength link but enables the carrier to retain very low fibre counts, yielding significantly lower operating costs.

WDM-PON has the native ability to span distances of 100km. This reach exceeds the capabilities of TDMA-based PON technologies such as Ethernet PON (EPON) and Gigabit PON (GPON) and enables carriers to bypass existing local offices (LOs), consolidating traffic into one central office. Deutsche Telekom for example recently announced that it will introduce WDM technology into its access network and reduce its number of LOs from 9,000 to fewer than 900.

Why is WDM-PON necessary?

Business services have always been developed in a symmetrical fashion, ie bandwidth demands to and from customer sites were largely identical. Conversely, bandwidth requirements of residential users have traditionally increased in mainly one direction – towards the customer. However, carriers are starting to see an increase in bandwidth being used to transport data upstream, driven by peer-to-peer applications. If this growth continues, it is estimated that bandwidth demands could soon increase to 100Mbit/s for residential customers and over 10Gbit/s for business users. Carriers will need to upgrade their access network infrastructures with technologies that can scale to meet their customer demands.

Don’t other PON solutions already exist?

While other PON solutions have existed for some time, largely in the form of EPON and GPON, their application focus has been the best-effort residential services market. These PON technologies are not suitable for business or carrier wholesale services and cannot therefore support a converged access and backhaul strategy. Indeed, E/GPON are currently only able to support and aggregate capacities of 1Gbit/s and 2.5Gbit/s respectively, which needs to be shared among all users. Standardisation for 10Gbit/s aggregate capacity is on its way, but sharing a limited bitrate among multiple users is an insufficient approach for future-proof access networks.

What’s the impact on carrier networks?

Today’s access networks have become an increasingly complex infrastructure. The wealth of competing technologies and protocols is rapidly inflating operating costs and creating ever-greater energy demands. WDM-PON enables carriers to develop a simpler, more efficient and ultimately greener network. By using technology that can support high bandwidth, high splitting ratios and long reach in the access network, carriers are able to eliminate unnecessary switching and routing equipment in LOs and converge business, residential and mobile backhaul services onto one unified infrastructure.

Is this a change in ideology?

Migration to a WDM-PON access network requires a carrier to reassess how it views its network topology. Indeed, this migration represents a significant change in ideology. It is not only a move away from operating parallel purpose-built platforms for different user groups to one converged access and backhaul infrastructure. It is also a change from today’s energy-demanding and labour-intensive switch and router systems to a simplified, energy-efficient and transport-centric environment.

Aside from the associated opex savings of such a migration, a WDM-PON based network is capable of moving fibre much closer to the customer, and this is imperative for carriers as they seek to answer their customers’ growing bandwidth demands. Is WDM-PON all about the bottom line?WDM-PON not only reduces the amount of equipment needed, it also heavily impacts on a carrier’s energy demands. WDM-PON enables carriers to concentrate energy-hungry and complex data-processing technology in a few centralised locations and serve a wider end user community with a lean, largely passive transport technology that requires little power and maintenance.

Can WDM-PON answer bandwidth demand?

The launch of applications such as the BBC iPlayer is already placing considerable strain on today’s networks. The BBC iPlayer alone is expected to account for 10% of the UK’s internet traffic by the end of 2008. What will happen when these services become high definition? To retain a profitable business model while still answering customers’ demands, carriers need to adopt new simpler networking topologies that will ensure their sustainability and growth in years to come.

Stephan Rettenberger

Director of Product Marketing, Adva Optical