Looking forward

By now, the readers should have walked through the journey with us via the past chapters observing how PON has evolved from various flavors of TDM PON (from the initial concoction of APON to currently deployed BPON, EPON, and GPON) to WDM PON with potential huge bandwidth provisioning; to OFDM PON with the benefits of high speed transmission, finer granularity of bandwidth provisioning, and color-free ONUs; to hybrid optical and wireless integration in provisioning mobility; and to green PON in the effort to reduce information and communication technology (ICT) carbon footprints. Currently deployed single-channel TDM PON systems will not likely be able to meet the ever growing traffic demands, both in quantity and variety, in the future. We will quickly recap what have transpired from the previous chapters in looking forward to what will likely actualize in the future. The PON evolution has continued, initially, in two stages: mid-term and long-term. The basic requirement of the evolution is achieving higher bandwidth, defined as NG-PON1 and NG-PON2, respectively, by the GPON interest group of the Full Service Access Network (FSAN). Specifically, FSAN has decided that the mid-term NG-PON1 should coexist with the currently deployed GPON systems and reuse the outside plant based on the current optical components and cost control. That is, the main requirement of NG-PON1 is compatibility. Besides, NG-PON1 was specified to provide even larger power budget so as to achieve increased split ratio and reach distance. In order to achieve these goals, NG-PON1 adapts advanced optical devices. The standardization of the asymmetric bandwidth edition of NG-PON1 was defined in XG-PON1, which was published in 2010 by FSAN and ITU-T in the ITU-T G.987 series [47]. It provides 10G downstream/2.5G upstream data rate. XG-PON2, another enhanced version for GPON mid-term evolution, was recommended to provide 10G/10G symmetric bandwidth and is not yet standardized (at the time of this writing). For the long-term development, NG-PON2 is still under discussion. Unlike NG-PON1, NG-PON2 can be an entirely new PON technology without considering the legacy PON compatibility constraints but with the overmatching of the legacy PON in terms of bandwidth, distance, security, and some other aspects. In evolving from NG-PON1 to NG-PON2, more technologies can be adopted into this long-term evolution.