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Omar Ahmad Abdel Aziz Mashaal Paper for Opt Comm Course

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  Optical Communication, Assignment . FKE, UTM.OCT, 2009 Prepared for: PROF.ABU BAKAR  Abstract   —    Gigabit-capable Passive Optical Network (PON) systems have been standardized and are now being deployed widely around the world such as GPON (standardized in ITU-T Rec. G.984 series) and 1G-EPON (IEEE 802.3ah, now part of IEEE 802.3-2008). While, GPON and 1G-EPON capacity are not enough by the next few years, because of the continuous increase in bandwidth demand. Therefore the need for a new higher capacity access network is more desirable. This paper presents the expected next generation PON by looking for the latest activities of the two Standard Development Organizations (SDOs), i.e. 10G-EPON in IEEE, as part of P802.3av, and NG-PON in FSAN/ITU-T. Keywords: 10G-EPON,NG-PON1,XGPON1,XGPON2,NG-PON2,WDM-PON,CDM-PON,TDMA-PON,IEEE,FSAN /ITU-T. I.   INTRODUCTION The next generation applications and services such as high-definition Television (HDTV), video on demand (VoD), videoconferencing, e-learning, interactive games, voice over IP, and others, are bandwidth  –  hungry applications and services. Therefore, a new generation of high capacity access network is needed. Providing higher bandwidth than the existing ones and a low deployment cost, since customers are not willing to pay for an increased bandwidth of the network ,are the key requirements of the new access networks.  Nowadays, there are several technologies providing broad  band access services as follows: Digital Subscriber Loop (DSL), Coaxial cable, wireless, and FTTX (FTTX stands for fiber to the X, where X stands for home, curb, neighborhood, office, business, premise, user, etc.)[1]. Table 1 lists the  bandwidth (per user) and the reach of these competing technologies [1].We can see from Table 1 ,in general, the XPON has the highest reach distance with highest  bandwidth/user, while bandwidth/user and reach are limited for the copper-wire and wireless access technologies, due to the physical media restrictions. Therefore to satisfy the increasing bandwidth demands without a huge increase in deployment cost, service provider will need to deploy Passive optical network (PON) as an access network. A number of passive optical networks (PONs) have been standardized to provide broadband access services including ATM PON and broadband PON (APON and BPON, respectively; ITU G983), Gigabit PON (GPON; ITU G984), and Ethernet PON (EPON; IEEE 802.3ah) [1] .These networks employ time-division multiplexing (TDM) to achieve cost effectiveness and have been widely accepted as the current-generation optical access solutions [1]. On the other hand TDM-PONs are suffering from many disadvantages such as, the capacity is limited and the  possibility to upgrade them is difficult. Therefore TDM-PON now is mature technology and the need for the next generation PON is more desirable. The NG-PON should satisfy the following features, connecting a large number of end-users at lower cost per user and delivering elastic bandwidth on-demand. Furthermore, it should be up-gradable without modification to the Outside Plant (OSP). In the meantime NG-PON systems are currently under standardization in two Standard Development Organizations (SDOs), i.e.10G-EPON in IEEE, as part of P802.3av, and NG-PON in FSAN/ITU-T [2]. This paper is organized as follows. Section II, reviews the current generation TDM-PON technologies. Section III, investigates the activities of several SDOs in developing the  NG-PON. Section IV and V discuss the expected IEEE and FSAN/ITU NG-PON systems which are under standardization respectively.  Next Generation Passive Optical Network ―PON‖   Omar Ahmad Abdelaziz Mashaal TABLE 1 BANDWIDTH/USER AND MAX REACH OFVARIOUS ACCESS TECHNOLOGIES [1] Service Bandwidth/user Max Reach ADSL 20 Mb/s (typical) 5.5 km VDSL 20 Mb/s(typical) 1 km Coax 2 Mb/s* 0.5 km Wi-Fi 54 Mb/s (max) 0.1 km WiMax 28 Mb/s (max) 15 km BPON 20 Mb/s* 20 km EPON 60 Mb/s* 20 km GPON 40 Mb/s* 20 km  Optical Communication, Assignment . FKE, UTM.OCT, 2009 Prepared for: PROF.ABU BAKAR II.   PON  OVERVIEW  PON enjoys a dominant position in the access technologies used in the access markets. High signal rate, format transparency, long distances, low cost and high reliability these features are the main reason behind the large scale deployment of PON around the world. The current generation PONs are TDM networks. A typical TDM-PON architecture is shown in Fig.1 which is a passive fiber tree topology. Separate light waves at λ1   and λ2 are used to carry the traffic from the central office ( CO) to an end user (downstream) and from an end user to the CO (upstream), respectively. The optical line terminal (OLT) and the optical network unit (ONU) are deployed as the two ends of the passive optical distribution network (ODN) [1]. The tree topology allows flexibility and minimizes the number of network splits, thus reducing the optical power loss and increasing the physical reach [1]. Moreover in TDM-PONs the hardware and the bandwidth at the user end are shared among users which decrease the cost. On the other hand, TDM-PONs have only one wavelength for downstream data and one for upstream data, thus limiting the average bandwidth per user to a few tens of megabits per second [4], also, the tree topology of current-generation TDM-PONs prevents features such as protection and restoration[3]. PON is a point-to-multipoint network, which requires multiplexing techniques to provide multiple-access capability. In TDM-PONs, TDM is used for users to access and share the  bandwidth in time domain [1]. To be more precise, we can say that, TDM PON do not have the best capacity and upgrade  possibility but due to its low cost and the use of passive components make them the current architecture of choice. The TDM PONs standards are summarized in the next paragraph. . The current generation standardized PON family includes three members as follows: Broadband PON (B-PON), Ethernet PON (E-PON) and Gigabit PON (G-PON). B-PON is the oldest member of the PON family and ATM based technique. The initial deployment of PONs was focused on B-PON technology but due to its low bit rate (622Mbps) nowadays this technology become mature. The second member of the PON family is E-PON which is an IEEE standard which uses Ethernet for packet data and it supports (1250 Mbps) bit rate, moreo ver it’s widely deployed. However E-PON still may not be scalable enough for HDTV and other high BW applications. The youngest member of the PON family is G-PON which can be seen as the next generation of B-PON. G-PON supports ATM and Ethernet protocols. To make the issue of PON family standards easier a comparison  between the three members is summarized in Table 2which compares three standardized TDM-PONs. G-PON (ITU-T G.984) has the maximum bit rate (2.488Gbps) with the longest reach (20km) and highest split ratio (1:64) but it has the highest deployment cost. E-PON is the direct competitor of G-PON it has the highest bit rate per user but the lowest split-ration and span. However, G-PON and E-PON has been deployed in large scale which make them the base for the next generation optical networks. The next section is going to discuss NG-PON activities in various Standard Development Organizations (SDOs).   TABLE 2 TDM-PON COMPARASION Characteristics BPON EPON GPON Standard ITU-T G.983 IEEE 802.3ah ITU-T G.984 Protocol ATM Ethernet Ethernet/ATM Rates (Mbps) down 622 1250 2488 Rates (Mbps) up 155 1250 1244 Split-ratio 1:32 1:16 1:64 Avg.Bitrate/user(Mbps) 20 60 40 Span (km) 20 10 20 Video RF RF/IP RF/IP Estimated cost Low Lowest Medium *Bit rates depends on the number of users, and the number listed here is a typical values Fig .1.TDM-PON Architecture.  Optical Communication, Assignment . FKE, UTM.OCT, 2009 Prepared for: PROF.ABU BAKAR III.    NG-PON   ACTIVITIES   IN   VARIOUS   SDO S  The NG-PON complete system is under development and standardization by two SDOs. IEEE is currently working on the development of 10 Gbit/s extensions for EPON system, under the P802.3av 10G-EPON Task Force [2]. The task was formed in September 2006 and it’ s expected to be finished, P802.3av 10G-EPON standard, in September 2009. At the same time, development activity for NG-PON system is under way at FSAN, which is working on consensus draft recommendations to be submitted to ITU-T SG15 Q2 for approval in September 2009 (G.987.1 and G.987.2specifications) and mid 2010 (G.987.3 and G.987.4 specifications)[2]. As expected, on 24 of September2009, FSAN announced the NG-PON1 White Paper, which is the framework for the XG-PON (10 Gigabit-capable PON) specification, has been reviewed and accepted for publication  by the IEEE communications magazine in November 2009 issue. The scope of the XG-PON specification, expected to be finalized in September 2009, includes the terminology framework, system requirements, and physical layer aspects, and will bring the FSAN standard to an equivalent level of completion vs. the 'to-be-announced' 10G EPON standard by IEEE. In addition, the XG-PON specifications also take operators' requirements of management and maintenance into consideration. The transmission convergence and management  parts of XG-PON specifications are expected to be finished in mid-2010 [6]. Fig.2, shows the past and ongoing IEEE and ITU-T standardization activities for various PON system generations. For instance, it is not clear how much convergence between the two next standards; however a discussion between both standardizing groups to make  potential convergence at both physical (PHY) and medium access control (MAC) levels. There are also other SDOs focusing only on selected aspects of ngPON systems, e.g. BBF working on the XPON architecture aspects [2].   IV.   IEEE   10G-EPON   (P802.3 AV ) 1G-EPON is widely deployed, for example, in Japan only there is more than 13 million subscribers are served through 1G-EPON FTTH system [7]. Second, in many developing countries, the major part of broadband users are living in multiple dwelling units (MDUs), therefore FTTB is the appropriate way to provide broadband services for them[8].For example, if each MDU ONU provides services to 24 subscribers and 32 ONUs are connected to one OLT, one EPON can serve 768 subscribers[8]. Third, wireless networks need EPON as a backhaul. On the other hand, the capacity of 1G-EPON is not enough for the newly high bit rate applications and for the fourth generation of mobile communication needs. Therefore the bandwidth of 1G-EPON should be increased. 10G-EPON is the natural upgrade for 1G-EPON. In the mean time, 10G- EPON being defined by IEEE 802.3av Task Force (TF) is expected to be standardized late 2009. There is a list of requirements and challenges are waiting the developers of the 10G-EPON that should be satisfied in the new EPON system. The requirements and challenges are:-    The co-existence and backward compatibility with the currently deployed 1G EPON to assure smooth transition path from 1G-EPON to 10G-EPON equipment and to avoid a significant loss in the capital expenditure investment of the 1G-EPON.    Wavelength allocation plan for 10 Gbit/s EPON systems must take into account existence of 1G-EPON equipment on the same PON plant for  both downstream and upstream channels [10]. Fig .2.Optical access technology evolution [5].  Optical Communication, Assignment . FKE, UTM.OCT, 2009 Prepared for: PROF.ABU BAKAR    Also 10G-EPON is faced with. PHY layer challenges include dispersion penalties and decreased receiver sensitivity, due to the 10-fold increase of the data-rate, non-linear effects in the Optical Distribution Network (ODN) due to high launch  powers for newly introduced 29 dB power budgets, together with inherent jitter and clock recovery  problems due to dual rate operation [2]. These challenges are expected to be resolved by 2009Q3  –   2010Q2. Some research papers have discussed several designs that satisfy the requirements and challenges mentioned above. The latest paper, which addressing 10G-EPON the major technical specifications, was issued in IEEE website on September 2009, reference number [9]. The most important specifications from that paper and others are summarized as follows:-    10G downstream will adopt (1577-1590 nm) to co-existent with 1G downstream in (1480-1500nm), relying on high-power cooled laser sources, potentially in the form of amplified Externally Modulated Lasers (EMLs); while reserving 1540-1560nm for video overlay. For upstream all ONUs will use (1260-1360nm) to keep the cost of ONUs low, which allows  both asymmetric operation (downstream 10G and upstream 1G) and symmetric operation (both downstream and upstream 10G).Moreover, 1G and 10G downstream channels are wavelength multiplexed, creating two separate logical channels on the same optical plant, as illustrated in Fig.3[9].    Stream-based Forward error correction (FEC) in all 10 Gbit/s links, is mandatory based on the RS (255,223) code, which has better error correction  properties than FEC used in 1G-EPON. moreover FEC is based on the bit stream coding instead of the frame coding.[2],[9]    The new OLT device needs to provide the transparent operation to the current 1G/1G ONU by supporting dual media access control (MAC) stacks that to support the co-existence compatibility. To support backward compatibility, the new ONU device needs to operate at either 10G rate or 1G rate at a time. Fig.4 illustrates a typical design and implementation of 10G-EPON where the 1G/1G ONU currently deployed in the network will remain operational when other new types of ONU continue to be added onto the existing network over time. Other specifications were addressed such as types of OLT and ONU, dual rate burst mode receiver, dual rate dynamic  bandwidth allocation (DBA) Engine and downstream multicast was addressed in reference [9]. Table 3 provides the differences between 1G-EPON and 10G/EPON specifications. To save the capital expenditure investments, moving from 1G-EPON toward 10G-EPON will occur in a gradual manner (see Fig.4). The 10G/1G ONU is a first logical step to upgrade the network to support 10G downstream operation, and it is followed by the ultimate addition of symmetric 10G/10G ONU. The newly developed dual rate OLT needs to be  provided at the central office, which can support both legacy and emerging types of ONU [9].   Fig .3.EPON Wavelength allocation [9].
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