Drawbacks Of Gigabit Passive Optical Network Engineering Essay

As user demand additions, so update the current GPON bandwidth will be a challenge, since the MAC reference Media Access Control protocol is really complicated. Since TDM-PON ( Time Division Multiplex Passive Optical Networks ) holding a wavelength merely upriver and downstream wavelength that limit the mean bandwidth per user is a few 10s of Mbps [ 44 ] This consequences in a waste of available bandwidth of the fibre. Furthermore, the bing TDM-PON tree topologies losing characteristics, such as the protection and Restoration. [ 45 ]

4.1.2 Scalability

The current TDM-PON architecture limits the versatility of the web and the users require the installing of a wholly new PON capacity to function up to 32 users. A figure of new pages added revenue enhancement included in the OLT in the cardinal office ( CO ) is merely to function more users. It may non be an economical solution, since it involves complex wiring and supply. [ 44 ] [ 46 ]


In order to contract the predating TDM-PON, such as alternate architecture TDM / WDM PON-based loanblend used. WDM constituents are less expensive than the demand for bandwidth-intensive applications continues to turn, so HPON migration is inevitable in the close hereafter. WDM engineering allows efficient sharing of resources, a reconfiguration and scalability. Therefore, WDM-PON non merely eliminates the demand for multiple protocols and clip but besides provides a practical point to indicate, transparently allows the informations and safety. [ 44 ] [ 46 ]

The HPON architecture uses following mechanisms to minimise the entire system cost:

Uncooled constituents are employed at Optical Network Units ( ONUs ) .

Use of array waveguide grates ( AWGs ) doubles the figure of ONUs supported by fibre splitter based web.

Tunable optical masers and receiving systems used at Optical Line Terminal ( OLT ) to minimise entire figure of transceivers, therefore ONUs can modulate their upstream traffic onto the optical bearers generated by OLT. [ 46 ]


The overview of the architecture HPON including TDM-PON and WDM-PON subsystem as shown in Fig. [ 46 ] The basic topology is a star faux pas ring is inactive ( PON ) is credited. The faux pas ring is connected to the distant node ( RN ) , which are the centres of the stars. The burden is connected to the RN on the west side of the ring to speak and listen to the wireless sender and receiving system on the west side of the OLT. Similarly, the UN RN is connected to the east side of the ring to speak and listen to the eastern portion of the revenue enhancement OLT. There is a point-to-point connexion between the OLT and the RN each logical degree. The aggregator pealing wavelength non once more. In the event of a fibre cut, the entire RNA as the signal loss is detected, the transceiver at the other side of OLT for uninterrupted operation. [ 47 ]

Figure 4.1: Architecture of Hybrid ( WDM/TDM PON ) [ 44 ]

4.4 Components

The basic constituents organizing the functional units of HPON architecture are Remote Node ( RN ) , Optical Network Unit ( ONU ) and Optical Line Terminal ( OLT ) which are discussed as under:

4.4.1 Distant Node ( RN )

RN basic construction shown in Fig. All but two of an NxN AWG end product ports are connected to the distribution fibres linking the burden associated with the RN. The set ‘s three-port device RN dividing thin-film filter performs add / bead functionality. [ 48 ] The first set spliting the left side ( LHS ) of the allocated Waveguide Grating ( AWG ) by interpolation / extraction of the UN on the right side ( RHS ) , and the 2nd centrifuge saloon on the right manus side ( RHS ) of the grid panoplied wave guide ( AWG ) by attention deficit disorder / bead, the UN left. The wavelength of a group / set by two delimiters must be different. [ 46 ] , so that each ONU ain dedicated wavelengths for transmittal of upstream and downstream in the DWDM grid communicate ol [ 45 ] . Since the interpolation of a AWG is about 6 dubnium, irrespective of the figure of ports, one of the more than eight ports can be used to bask a better power budget than a inactive splitter. Each RN is by and large used ONU 16-64 [ 48 ] [ 49 ] .

Figure 4.2: Distant Node with AWG [ 46 ]

4.4.2 Optical Network Unit ( ONU )

The comparatively high stableness of the specifications required upriver as AWG wavelength optical filters and out of the light way. The easiest manner to implement the UN tax-stabilized optical maser beginning is used. However, this consequences in the visible radiation and negatron bulky power hungry and therefore the impact of the cost of the web. The other attack is to utilize a tunable optical maser UN, but this would necessitate a control map in the OLT and the wavelength tunable optical masers are rather expensive. A 2nd attack is that of another semiconducting material optical amplifier ( SOA ) as a UN modulator shown in FIG. Responsibility for ambient visible radiation created by the OLT [ 46 ] . It is non necessary to stabilise the wavelength of the United Nations, and the signal can be amplified to increase the quality and the transmittal distance [ 45 ] [ 46 ] . Therefore, the United Nations has no local optical beginning and an optical modulator alternatively of modular optical uninterrupted moving ridge ( CW ) breaks received OLT for upstream transmittal. It should be noted that the tunable receiving system for the UN. The AWG the distant node removes unwanted wavelength and allows merely a specific wavelength to make each ONU. The UN receiving system merely needs adequate bandwidth for dense wavelength division multiplexing optical any sort ( DWDM ) channels used in the web. The MAC block in the United Nations non merely to look into the connexion between the upstream and downstream transmittals, but besides to organize the programming of the ballot by the OLT and describing mechanisms. [ 50 ] [ 51 ]

Figure 4.3: Block diagram of the HPON ONU, with optical bearer provided

Externally by OLT [ 45 ]

4.4.3 Optical Line Terminal ( OLT )

Figure shows the block diagram of OLT. Tunable constituents such as fast tunable optical masers and tunable filters are employed.

Figure 4.4: Block diagram of OLT for HPON [ 45 ]

Since the mean burden of the entree webs by and large low [ 46 ] , [ 52 ] , and therefore assumed statistical multiplexing addition tunable OLT shared constituents, which minimizes the transceiver count a given figure of ONU [ 45 ] , and therefore reduces the overall system cost. This agreement is besides good in footings of scalability: the figure of users additions or extra web traffic, tunable optical masers and receiving systems are added to the OLT. Circulators separate the optical signals upstream of the downstream signals. The coder controls the operation of tunable senders and tunable receiving systems. [ 50 ] The WDM coupling separates channel CWDM DWDM channels are presented. The CWDM demultiplexer by thin-layer demultiplexing filter is used for upstream traffic. [ 46 ] The end products of the optical encoder ( downstream ) of the controlled channel DWDM optical amplifiers, and enters port 1 of the circulator. The information, after a base on balls through port 2 of the pump and the WDM coupling in the optical entree web. DWDM upstream traffic channels through the WDM coupling of the circulator port 2 and port 3 of the circulator. The optical pre-amplifier may be used to increase the receiver sensitiveness. [ 50 ] [ 53 ] It should be noted that the downstream traffic, tunable senders used in OLT and continuous-wave ( CW ) optical transition of the current eruption, the United Nations model. With this constellation, merely half-duplex

the physical bed communicating is possible between the OLT and each ONU. [ 45 ] In contrast, a similar architecture [ 54 ] is a two-fiber ring, two visible radiation beginnings and two mux / demux execute full-duplex communicating, the success HPON architecture reduces the cost dramatically. In compensation, the MAC protocol requires carefully planned and scheduling algorithms to supply effectual communicating. [ 50 ]



The success of OLT WDMPON look into the sum of upstream traffic and the UN to direct financess saved, but the signifier of CW optical explosion than what the United Nations to convey upstream traffic. Since there is no separate control channel or a control message scheme embedded flight sequences [ 55 ] , the MAC protocol must trust on the in-band signaling, utilizing frame format shown in Fig. 3, in this study, and the Fieldss are set to give the vote procedure. Here, the “ ID ” of the 1-bits [ 46 ] was extended past frames 8-bit extension flags: the “ Frame Type ” flag is used to bespeak that the frame of the normal traffic or not.The Fieldss use is in the 8-bit flags is shown in Table. [ 46 ]

Table 4.1: Bit flags in downstream success WDM PON frame





Frame Type

-Normal Datas


2-15 -Unused


Force Report

-No action required

-ONU should describe in the corresponding upstream frame







Each ONU computes the sum of traffic waiting in its upstream traffic waiting line in eights through the study field in an upstream frame when the ‘Force Report ‘ field of a standard downstream frame is set, and the OLT uses the grant field to bespeak the existent size of each grant ( besides in eights ) . As shown in Fig. 4.5, the length of the whole CW explosion corresponds to that of all upstream Ethernet frames ( i.e. , the size of grant ) plus the study field and the operating expense. We use two control parametric quantities to regulate the polling procedure dwelling of coverage and allowing operations as follows:

ONU TIMEOUT: The OLT maintains a timer for the United Nations and back every clip you enter subsequently sent to the United Nations model. This resets the timer, if the right model is zero upper field were reported. If the clip bound expires after the clip of the UN, which means no upstream traffic, which was supported by the United Nations or describe message is lost during transmittal to the OLT, the OLT sends a new UN study support the timer once more and once more. This keeps the polling procedure parametric quantity passing, if the question message loss and limits the maximal polling rhythm. It besides affects the mean hold of packages upstream traffic when the system is under low burden.

MAX GRANT: This parametric quantity limits the maximal size of a grant ( i.e. , the payload portion of the CW explosion ) for ONU upstream traffic.

Figure 4.5: Frame formats for success WDM-PON MAC protocol [ 46 ]


An RN is either a inactive web arranger ( interface ) , or within one AWG. If an RN is a inactive splitter to divide wavelength DWDM web will be used to further widen the informations connected ONU RN. Equivalent duty senders of Fabry-Perot ( FP ) optical maser Wavelength Division direct informations upriver coarse grid ( CWDM ) grids. In add-on, each has its ain wavelength DWDM web dedicated to pass on ONU OLT if RN AWG is shown in Fig. Whereas about 6 dB interpolation loss AWG, irrespective of the figure of ports to guarantee that a port can be used with more than eight AWG better balance of power splitter is a inactive experiment. Each capable RN WDM-PON ONU 16-64 [ 56 ] . The downstream traffic and upstream traffic from the ONUs can utilize the same wavelength, but in different waies on the same fibre. The advantage of being based on CWDM and DWDM stars TDM, WDM star-based traffic equilibrium. The stars tend to function concerns WDM, TDM and the stars tend to function residential countries. Tunable constituents help cut down OLT revenue enhancement affairs. OLT tunable optical masers generate intermediate frames, and both uninterrupted moving ridge ( CW ) to split modulated by the United Nations. There is no local visible radiation beginnings are needed by the UN. This agreement consequences in the half duplex communicating with the OLT and each ONU. Compared with the traditional architecture, with two fiber rings, two visible radiation beginnings and two Mux / Demux devices perform full-duplex operation, this architecture dramatically reduces the execution costs [ 45 ] .

Figure 4.6: Functional architecture of HPON with AWG [ 45 ]


The figure shows the gradual constitution of bandwidth in optical entree webs HPON based architecture. Figure 4.6 ( a ) shows the bing TDM-PON tree topology connected to a cardinal office ( CO ) . All TDM-PON OLT own overseas telegram inside the CO Figure 4.6 ( B ) shows the first measure in the migration of the bing web substructure. Passive interfaces are replaced by the nurses Extrusion treating machines with a thin passive movie and add / bead filters, the debut of CWDM. The fibres in a PON web connexion is replaced with a individual fibre ring ironss served by the RN CO. Note that the distribution fibres affected by this migration. The United Nations in footings of suitableness of optical entree web is precisely the same, merely a short clip of inaction required for the ascent. Therefore, there is virtually TDM-PON ONU can run as earlier without major ascents. Figure 4.6 ( degree Celsius ) describes the 2nd stage of the migration. As the figure of users necessitating big bandwidth for future broadband applications, RNA, consisting a grid array wave guide ( AWG ) as a DWDM multiplexer / demultiplexer can be inserted into the web. In this instance, there is a dedicated DWDM channel between the OLT and each ONU. If the protection and recovery maps are implemented in the bing RNA utilizing semi-passive switch, infixing a new RN in the web does non interfere with the operation of the web in general. Figure 4.6 ( vitamin D ) shows the possible extension of the web. Given that a dedicated wavelength to the end product of the AWG, it can be used as a ring-PON backhaul web topology tree. Connecting the two PON fibre web can be connected to assorted RNA forms a protection way. To further better the capacity of the SOA ( semiconducting material optical amplifier ) aˆ‹aˆ‹based modulator can be replaced with a stabilized optical maser source-duplex operation. Therefore, the architecture is somewhat HPON pure TDM-PON web updates WDM-PON is an economical manner [ 50 ] .

Figure 4.7: Optical entree Network bandwidth up step scenario from bing TDMPON to HPON ( WDM/TDM based Hybrid PON ) [ 45 ]


In order to analyse the HPON web scalability in the figure of users and scope of links, two major restrictions of the budget and the web connexion is available wavelengths. The larger figure of users limit features of constituents, such as the maximal transmittal power, receiver sensitiveness loss and Paste. Let ‘s expression at the typical values aˆ‹aˆ‹for common criterions in table 4.1 [ 45 ]

Table 4.2: Typical specification of optical constituents [ 45 ]




Unit of measurement


Transmission power




Output power of FP optical maser




Receiver sensitiveness




Insertion loss: Thin movie add/drop




Propagation loss: fibre




Insertion loss of AWG




Loss: splice and aging on the nexus




Addition of SOA

10 – 25



Passive splitter dividing ratio

4 – 32



Noise figure of SOA



First, assume that web supports merely DWDM users, which means every RN has an AWG. We can presume that each RN can back up up to 32 ONUs. Let ‘Wt ‘ be the entire figure of ONUs. Then, the figure of RNs on the ring to back up Wt ONUs, X, is given by

aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦ . ( 1 )

Let ‘L ‘ be the maximum fibre length between OLT and any ONU. The power dividing ratio between receiving system subdivision and transition subdivision inside the ONU is 6 to 1.3dB.

The downstream traffic power budget must fulfill the undermentioned status in order for signal to be successfully received:

aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦ ( 2 )

Similarly the power budget for the upstream traffic can be estimated as:

aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦ ( 3 )

Note that for DWDM users, the upstream traffic has a tighter bond of power budget than that of the downstream traffic. In the same manner, we can deduce the edge for the figure of users and associate range presuming the web merely serves TDM-PON, in this scenario. The ONUs are holding low power FP Laser, here we derive link range sing to the upstream power budget: [ 44 ]

aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦aˆ¦ ( 4 )