Omar Ahmad Abdel Aziz Mashaal Paper for Opt Comm Course

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 bandwidthhungry 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



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 1 and 2 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, moreover its 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.



III. NG-PON ACTIVITIES IN VARIOUS SDOS

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 its 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 (P802.3AV)

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].



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].



V. FSAN/ITU-T NG-PON

The gigabit- capable passive optical network (GPON)

was developed by FSAN and was standardized by the

International Telecommunication Union-Telecommunication

Standardization Sector (ITU-T) a typical GPON system

provides 2.488 Gbps of downstream bandwidth and 1.244

Gbps of upstream bandwidth[11]. Having turned over the

work of GPON standard maintenance to ITU, FSAN is now

studying the next-generation access (NGA). The objective of

NGA is to facilitate high bandwidth provision, large split ratio,

and extended network reach. FSAN has planned two stages of

NGA evolution: NGA1 and NGA2 [12]. The categorizing of

FSAN/ITU NG-PON system into two categories, NG-PON1

and NG-PON2 generations, is based on their characteristics of

coexistence with legacy GPON systems.

A. FSAN/ITU-T NG-PON1 (G.987)

NGA1 focuses on PON technologies that are compatible

with GPON standards (ITU-T G.984 series) and compatible

with the current optical distribution network (ODN) without

the need to introduce any changes in the ODN or disrupt the

existing services for customers served over GPON [2],[11].

According to the upstream bit rate, NG-GPON1 is divided into

two systems XG-PON1and XG-PON2; both of them are

supporting 10Gbps downstream for the upstream data rate

2.5Gbps is supported by XGPON1 while a fully symmetric bit

rate, 10Gbps upstream, is supported by XNG-PON2. FSAN

operators elaborated a detailed list of system level

requirements for NG-PON1 systems, which is a direct

extension of former GPON system requirements, with the

main focus on system scalability into a larger number of

connected customers, better QoS measures and security

mechanisms [2]. According to FSAN there is five typical

candidate network architectures have been proposed for

NGA1 [12]. In this paper we will present two of them because

the first three candidates dont satisfy the 10Gbps rate.

1. XG-PON1 WITH 10-G DOWNSTREAM,

NX2.5-G UPSTREAM [11].

This architecture upgrades the downstream link capacity to

10 Gb/s. The difficulty with the architecture of 10 Gb/s is

enabling the burst mode time-division multiple access

(TDMA) operated at 10 Gb/s. Because of the limitation of

available components and design practices, many simple circuit techniques become impractical when the rate goes

beyond 5 Gb/s.

Fig .4.10G-EPON architecture design [9]

TABLE 3

1G-EPON AND10G-EPON COMPARASION [9]

1G-EPON 10G-EPON

Downstream wavelength 1490nm 1590nm or

1577nm

Upstream wavelength 1310nm 1270nm

Mode of operation Symmetric

only

Asymmetric or

symmetric

Forward error

correction

Optional and

frame based

Mandatory or

symmetric

PMD type

(point-to-multipoint)

PX10, and

PX20

PRX10,

PRX20, PRX30 PR10, PR20,

PR30

PCS line coding 8b/10b

64b/66b

Single channel broadcast

(SCB) LLID

0x7FFF

0x7FFE



Overcoming this limit requires specialized hardware and is

thus costly. To minimize additional investment, architecture

was proposed to upgrade only the downstream to 10 Gb/s, but

to use one or more 2.5-Gb/s wavelengths in the upstream as

shown in Fig.5. This architecture still can be considered as a

TDM system both in the downstream and upstream. The

downstream transmission is modeled as 32 ONUs sharing a

10-Gb/s link. Depending on the number of available upstream

wavelengths, the ONUs in the upstream scenario are divided

into a different number of groups operating at 2.5 Gb/s. If two

wavelengths are adopted in the upstream, the ONUs in the

upstream scenario are divided into two virtual groups, each of

which has 16 ONUs sharing a 2.5-Gb/s upstream link. If one

wavelength is adopted, it is abstracted as 32 ONUs sharing a

2.5-Gb/s upstream link.

2. XG-PON2 WITH10-G BIDIRECTIONAL [11]

When devices capable of a 10-Gb/s burst mode become

commercially available, the architecture with both the

downstream and upstream trans-mission being upgraded to 10

Gb/s can be realized (see Fig.6). In this case, the transmission

in both upstream and downstream can be abstracted as 32

ONUs sharing a 10-Gb/s link.

Among [11] the five candidate architectures, XG-PON1

architecture is a promising and economical architecture to

meet the future bandwidth requirement in NGA1. First, the

upstream and downstream bandwidths are increased to 2.5

Gb/s and 10 Gb/s, respectively. The increased bandwidths are

potentially able to accommodate the future bandwidth-

consuming applications in NGA1. Second, the 2.5-Gb/s burst

mode receiver requires lower cost compared to the 10-Gb/s

burst mode receiver in XG-PON2 architecture, making XG-

PON1 architecture a more economical solution for a GPON

upgrade. Essentially, the upgraded systems are still TDM

systems. By abstraction, the typical 32 ONUs in GPON are

divided into multiple virtual groups, where the ONUs in each

group share a link in TDM fashion. Hence, the five candidate

architectures can be regarded as TDM systems with different

link rates and different numbers of shared ONUs.

B. NG-PON2 AND WDM-PON ACTIVITIES

NG-PON2 is a long-term solution with an entirely new

optical network type [11]. The objective of NGA2 is to

provision an independent PON scheme, without being

constrained by the GPON standards and the currently

deployed outside plant. NG-PON2 at this time does not have

any preferred technology, and therefore a plethora of possible

access system implementations were submitted for FSAN

consideration, ranging from higher capacity multi-channel

TDMA PON, through WDM-PON, and ending with such

exotic systems as CDMA PON with dynamic code allocation

[2]. Each of these architectures features a number of technical

challenges which need yet to be addressed by industry and

academia, in order to provide a cost-effective solution suitable

for access network development. Higher capacity TDMA

PON systems will have to combat dispersion effects and

reduction in receiver sensitivity, which beyond 10 Gbit/s begin

to challenge support for higher power budgets targeted by

carriers to guarantee higher port densities at the CO sites.

WDM-PON will always be troubled by the use of wavelength

selective devices at the ONU side. Despite rapid progress in

the colorless ONU transceivers (via the use of RSOA devices

or tunable lasers), such solutions remain at this time

substantially more expensive when compared with existing

TDMA PON transceivers, thus failing to meet the test of cost-

efficiency that so many technologies have already failed in the

access domain.

Fig .5.XG-PON1 proposed architecture [11].

Fig .6.XG-PON2 proposed architecture [11].



More exotic approaches, mainly in the form of CDMA PON

systems, have the form of research projects at this time, with

numerous technical and system-level challenges, struggling

with basic research and material limitations, imposing

constraints typical PON architectures have never faced before.

[2]

From the existing NG-PON2 technologies, WDM-PON

seems to have the nearest commercial future, provided that

emerging customer applications support delivery of dedicated

high capacity bandwidth pipes to each customer. A number of

commercial WDM-PON systems are already available for

deployment, though their market share is very limited, mainly

due to limited carrier interest and high deployment and

maintenance costs, as well as lack of customer interest, except

for business customers, who are typically served with P2P

solutions at this time [2].

Table 4 summarizes the activities of many research and

development organizations, including the project name

objective, key technology, and the sponsor.

VI. CONCLUSION

After reading more than fifteen papers I have concluded

the following points. The plan to migrate from the current

PON to the NG-PON will occur in two phases, short term and

long term. Phase one, is the short term one which is under

standardization which includes 10G-EPON and 10GPON

by two SDOs, IEEE and FSAN/ITUT respectively which is

expected to be ready for implementation in the next two years.

The closer cooperation between IEEE and ITU-T may

eventually result in increased convergence between ngPON

systems, at least in the PHY layer, The main feature of phase

one is to extend the already access network architecture into

higher capacity, capable of supporting future customer

applications. IEEE ,10G-EPON standard is the most

promising one because it will provide the highest transmission

capacity, the lowest cost per user and the easiest way to

upgrade from 1Gbps to 10 Gbps. On the other hand, because

of the large scale deployment of 10GPON, it will be the NG-

PON for many countries despite of the 10G-EPON features.

Therefore, the financial factor is affecting the NG-PON

technology.

Phase 2, is the long term plan which will be independent

from the current TDM-PON. For the meant time, is not clear

how the architecture will be arranged and which technology is

going to be used for the phase2. Many papers are proposing

the WDM-PON for the long term phase, because its capable

to provide virtual point to point communication which can

provide a huge bit rate to the users, but still the financial factor

and the available technology restrict the migration to WDM-

PON.

TABLE 4

NG-PON projects

Standard Project Name Objective Key Technology Sponsor

NG-PON 1

Burst Mode Transmission Toward 10Gbps BM-CDR

Dual loop (DLL + PLL) and

synchronization

Stanford

SUCCESS-LCO (Line

Code Overlay)

Co-existence of 2.5G and

10G on the same

Spectral line coding KDDI Labs

SUCCESS-DWA

(Dynamic Allocation)

Smooth upgrade from 1 to

N s

Tuneable lasers and AWG

KDDI Labs

NG-PON2

success- H PON (Hybrid

TDM/WDM

Co-existence of TDM

and WDM PONs

RSOA and ring

architecture

Motorola

Multi-Wavelength Multi-

Rate NG-PON

Co-existence of 2.5-

10G over multiple s

SOA and burst mode

transmission

Huawei

SureON (Secure Optical

Network)

Enhance physical layer

security

PON attack detection

and countermeasure

ANDevices

LEON (Latchable)

Reconfigurable and

passive remote node

Latchable optics

NSF



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Omar Ahmad Abdel Aziz Mashaal Paper for Opt Comm Course

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