Continued… DWDM Part IX

For the past eights parts, I’ve shared more on introduction of DWDM (DWDM 101) and in previous DWDM Part VII, I’ve also shared on DWDM as 3rd option for service providers to provide an economical solution in resolving fiberoptic capacity crisis. Having so much said on DWDM 101, DWDM Part IX onward will focus more on its industrial application and today I’ll start on sharing the info on WDM-PON technology for broadband access that utilizes CWDM or DWDM.

PON

The passive optical network (PON) is an optical fiber based network architecture, which can provide much higher bandwidth in the access network compared to traditional copper-based networks. Incorporating wavelength-division multiplexing (WDM) in a PON allows one to support much higher bandwidth compared to the standard PON, which operates in the “single-wavelength mode” where one wavelength is used for upstream transmission and a separate one is used for downstream transmission. The WDM-PON is becoming a revolutionary and scalable broadband access technology  that  will  provide  high  bandwidth  to  end  users.

The access network, also known as the “first-mile network,” connects the service provider central offices (COs) to businesses and residential subscribers. This network is also commonly referred as the subscriber access network, or the local loop. As we all know that the bandwidth demand in the access network has been increasing rapidly over the past several years. Residential subscribers demand first-mile access solutions that have high bandwidth and offer
media-rich services. Similarly, corporate users demand broadband infrastructure through which they can connect their local-area networks to the Internet backbone.

The predominant broadband access solutions deployed today are the digital subscriber line (DSL) and community antenna television (CATV) (cable TV) based networks. However, both of these technologies have limitations because they are based on infrastructure that was originally built for carrying voice and analog TV signals, respectively; but their retrofitted versions to carry data are not optimal. Currently deployed blends of asymmetric DSL (ADSL) technologies provide 1.5 Mbits/s of downstream bandwidth and 128 Kbits/s of upstream bandwidth at best.

Note: In Malaysia, the biggest ADSL service is known as “streamyx” provided by the incumbent service provider TM (Telekom Malaysia).

Moreover, the distance of any DSL subscriber to a CO must be less than 5,486 meters (18000 ft) because of signal distortions. Although variations of DSL such as very-high-bit-rate DSL (VDSL), which can support up to 50 Mbits/s of downstream bandwidth, are gradually emerging, these technologies have much more severe distance limitations. For example, the maximum distance over which VDSL can be supported is limited to 457 m (1500 ft). CATV networks provide Internet services by dedicating some radio frequency (RF) channels in a coaxial cable for data. However, CATV networks are mainly built for delivering broadcast services, so they don’t fit well for the bidirectional communication model of a data network. At high load, the network’s performance is usually frustrating to end users.

Source:  Wavelength-division-multiplexed passive optical network (WDM-PON) technologies for broadband access by Amitabha Banerjee and others, Optical Society of America.

To be continued… DWDM Part IX

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