Media Access Control and Resource Allocation

Over the past decade of unprecedented advances in information and communications technology (ICT), a variety of bandwidth-demanding applications, including Internet access, e-mail, e-commerce, voice over internet protocol (VoIP), video conferencing, Internet Protocol Television (IPTV), and online gaming, have emerged and been rapidly deployed in the network. As the Internet traffic grows, it is becoming urgent to efficiently manage, move, and store increasing amount of mission-critical information, thus accelerating the demand for data storage systems. Consequently, the traffic in both public and private communication networks has experienced dramatic growth. As reported by Cisco’s visual networking index, the Internet traffic in 2011 has reached around 28 k petabytes per month while it was less than 200 petabytes per month in 2001 [1]. According to the sixth annual Cisco(R) Visual Networking Index (VNI) Forecast (2011–2016) [2], global IP traffic has increased eightfold over the past 5 years, and will increase 4-fold over the next 5 years. In 2016, global IP traffic will reach 1.3 zettabytes per year or 109.5 exabytes per month. Overall, IP traffic will grow at a compound annual growth rate (CAGR) of 29% from 2011 to 2016. Therefore, to meet the challenge caused by the increased network traffic, telecommunication service providers and enterprises are driven to enhance their networks in providing enough bandwidth for new arising services.

Passive Optical Network (PON) [112] is a set of technologies standardized by ITU-T and IEEE, although it is originally created by the Full Service Access Network (FSAN) working group. PON is a converged infrastructure that can carry multiple services such as plain old telephony service (POTS), voice over IP (VoIP), data, video, and/or telemetry, in that all of these services are converted and encapsulated in a single packet type for transmission over the PON fiber. PON consists of three main parts [63].

The protocol stack of GPON systems, as depicted in Fig. 3.1, is specified in ITU-T G.984 series [20, 29, 46].

IEEE802.3ah standardized the MultiPoint Control Protocol (MPCP) as the MAC layer control protocol for EPON [138], and IEEE802.3av specified MAC layer protocols for 10G EPON. For the MAC layer and layers above, in order to achieve backward compatibility such that network operators are encouraged to upgrade their services, 10G-EPON keeps the EPON frame format, MAC layer, MAC control layer, and all the layers above almost unchanged from 1G-EPON [104, 131]. This further implies that similar network management system (NMS), PON-layer operations, administrations, and maintenance (OAM) system, and dynamic bandwidth allocation (DBA) used in EPON can be applied to 10G-EPON as well.

By taking advantage of the huge bandwidth provision of wavelength channels, wavelength division multiplexing (WDM) passive optical network (PON) has become a promising future-proof access network technology to meet the rapidly increasing traffic demands resulted from the popularization of Internet and sprouting of bandwidth-demanding applications [7, 126]. In WDM PON, a number of wavelengths are used to provision bandwidth to ONUs in both upstream and downstream, rather than sharing a single wavelength in each stream in TDM PON. Since ONUs may share the usage of a number of wavelengths, a MAC layer control protocol is needed to coordinate the traffic transmission such that the collision between traffic from different ONUs can be avoided.

Orthogonal frequency division multiple access PON (OFDMA PON) employs orthogonal frequency division multiplexing (OFDM) as the data modulation scheme to increase the provisioning data rate. Qian et al. [89] demonstrated the transmission of 108 Gb/s downstream data rate over a type B fiber with a split ratio of 32. Figure 6.1 describes one typical OFDMA PON architecture. OFDMA PON uses OFDMA as an access scheme [90, 111], which divides the upstream/downstream bandwidth in baseband into multiple subcarriers with orthogonal frequencies. These subcarriers are dynamically allocated to different ONUs based on their real-time incoming traffic information. As compared to TDM PON and WDM PON, OFDMA PON enjoys numerous advantages such as high speed transmission, fine granularity of bandwidth allocation, and color-free ONUs [137].

Optical access networking provisions high bandwidth in order to meet increasing traffic demands of end users. However, the optical solution lacks mobility, and thus limits the last mile penetration. By provisioning mobility, a rather desirable feature, to optical access, hybrid optical and wireless networks are becoming an attractive solution for wireline access network operators to expand their subscriber base [74, 99–101, 128].

The future sees a clear trend of data rate increase in both wireless and wireline broadband access. These access networks may experience a dramatic increase of energy consumption in provisioning higher bandwidth as well as for other reasons [8, 28, 61]. For example, to guarantee a sufficient signal-to-noise ratio (SNR) at the receiver side for accurate recovery of high data rate signals, advanced transmitters with high transmitting signal power and advanced modulation schemes are required, thus consequently resulting in high energy consumption of the devices. Also, to provision a higher data rate, more power will be consumed by electronic circuits in network devices to facilitate fast data processing. Besides, high-speed data processing incurs fast heat buildup and high heat dissipation that further incurs high energy consumption for cooling. It is estimated that the access network energy consumption increases linearly with the provisioned data rate. It has also been reported that the LTE base station (BS) consumes more energy in data processing than the 3G UMTS systems [108, 119], and the 10 Gb/s Ethernet PON (EPON) system consumes much more energy than the 1 Gb/s EPON system. This chapter focuses on green passive optical networks, the wireline aspect discoursed in great details on how to green broadband access networks [30].

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.