Self-protected ring-star-architecture TDM passive optical network with triple-play management

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Self-protected ring-star-architecture TDM passive optical network with

triple-play management

C.H. Yeh

a,

⁎

, C.W. Chow

b

, Y.L. Liu

a a

Information and Communications Research Laboratories, Industrial Technology Research Institute (ITRI), Chutung, Hsinchu 31040, Taiwan

b_{Department of Photonics and Institute of Electro-Optical Engineering, National Chiao Tung University, Hsinchu 30010, Taiwan}

a b s t r a c t

a r t i c l e i n f o

Article history:

Received 12 January 2010

Received in revised form 14 March 2011 Accepted 14 March 2011

Available online 2 April 2011 Keywords:

Fiber-fault Self-protection TDM-PON CATV

A new self-protected apparatus in ring-star-architecture for time division multiplexed passive optical network (TDM-PON) against fiber-fault; together with triple-play management in optical layer is proposed and investigated. Different scenarios offiber-fault locations are also discussed and analyzed. Besides, the performance of data traffics in both uplink and downlink directions are also measured and studied. Standard CATV video signal distribution to each ONUs is also performed, showing the proposed access network cannot only have self-restored function, but also can manage triple-play services in the optical layer.

1. Introduction

Recently, due to the development of high speed and high capacity Internet, IP telephony, Video on demand (VoD), IP television (IP-TV), interactive gaming, and video conference etc., the requirement of broadband services is accelerated. Thus, passive optical network (PON) is regarded as the most promising candidate forﬁber to the home (FTTH) access network because of its beneﬁts of low cost, long transmission length, high capacity and bandwidth, and multi-service convergence[1]. Hence, the Ethernet PON (EPON) and Gigabit PON (GPON) have already been standardized and they are currently operating at nominal line rates of 1.25 and 2.5 Gb/s, respectively[2,3]. The existing TDM-PON systems can provide triple-play services: data, voice and video, for users with guarantee quality of service (QoS). In the standard triple-play access systems, the downstream signal (1490 nm) and video signal (1550 nm) from the optical line terminal (OLT) are broadcasting to each optical network units (ONUs), and the upstream signal (1310 nm) of each ONU is transmitted to the OLT by TDM framing

[2–5]. However, if aﬁber-fault occurs between the OLT and ONU, data trafﬁc will be disconnected. Therefore, several protection technologies have been performed and analyzed in PON systems[6–8]. In triple-play system, the downlink (1490 nm) and uplink (1310 nm) are required, however, the video service (1550 nm) is optional. In present systems, if an ONU does not want the video service, the OLT cannot control and manage whether the video service (such as CATV and IP-TV etc.) allows into each ONU according to the Standard[2].

In this study, we propose and demonstrate a self-restored ring-star architecture for TDM-PON system against ﬁber failure. The new proposed OLT and ONU modules are used in the proposed PON system to achieve self-healing function. Here, we also design a simple control module in each ONU for controlling the video distribution directly in the optical layer. In addition, the performance of the proposed PON architecture has also been discussed.

2. Experiments and results

Fig. 1 shows the proposed ring-star-architecture for TDM-PON system with theﬁber-fault protection and video service management function simultaneously. InFig. 1, the red, blue and green arrow lines represent the downlink, uplink and video signals, respectively. The downlink and video signals couple together by WDM coupler (WC) and are shared to each ONU by a 1 × N splitter (S). In remote node (RN), we use a 2 × N splitter (S) to connect the OLT and ONUs. In the inset ofFig. 1

(ONU structure), we add two 1 × 1 optical switches (OS1and OS2) and a

2 × 2 optical coupler (CP) on each ONU to achieve self-restoration and video service management. Each ONU in the proposed PON system is interconnection in the ring architecture and the OS1is used to connect to

the protectingﬁber (dash line). In the inset ofFig. 1(OLT structure), we add a 1 × 2 optical switch (OS3) in the OLT for selecting the transmission

path between the workingfiber (solid line) and the protecting fiber (dash line). Initially, the OS3is switched to connect the workingfiber for

transmitting downlink and video signals to each ONU under normal status and the OS1in the ONU is at“off state” to block the uplink signal

transmitting into the protectingﬁber, as illustrated inFig. 1.

Generally, there could be twofiber-faults: in the feeder fiber and the distributedfibers in the PON. For the proposed PON architecture, if a Optics Communications 284 (2011) 3248–3250

⁎ Corresponding author at: Bldg. 14, 195, Sec. 4, Chung-Hsing Rd., Chutung, Hsinchu 31040, Taiwan.

E-mail addresses:[email protected],[email protected](C.H. Yeh).

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Optics Communications

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ﬁber failure occurs in feeder ﬁber (between OLT and RN), as seen in

Fig. 2, the entire data trafﬁc is blocked. This means the OLT cannot broadcast downlink and video signals to each ONU and cannot receive uplink signals from all ONUs. Then, in our proposed network architecture, the MAC of OLT will switch the OS3 immediately to

connect to the protecting feederfiber for reconnecting for the entire data traffic. At this time, the protecting fiber can be regarded as a workingfiber. While the fault is restored, it would become to the protectingfiber.

Next, while an occurrence of fault in the distributedﬁber (between RN and ONU1), as shown inFig. 3, the ONU1could not connect to the

OLT. At this moment, the OS1of ONU1would be turned on to connect

to the protectingﬁber. The uplink data will pass through the CP of ONU2 to reconnect to the OLT. This means that each ONU can

reconnect to the OLT by transmitting data through the neighbor ONU to achieve self-restoration againstﬁber-fault, as illustrated inFig. 3. Besides, while twoﬁber-faults occur between RN and ONU1and RN

and ONU2simultaneously, the ONU1and ONU2cannot connect the

OLT. Thus, according to the proposed protected mechanism, the OS1of

ONU1and ONU2would be turned on to connect to the protectingﬁber

with the adjacent ONU simultaneously, as illustrated inFig. 4. It means that the ONU1and ONU2could reconnect the data trafﬁc transmitting

through the ONU3. Based on the same principle, if several distributed

ﬁbers are cut, the affected ONUs can shared the same distributed ﬁber with the surviving ONU.

Moreover, while the fault faults occur both at the feeder and distributedﬁbers, each ONU cannot receive the downlink and video

signals from OLT. At this moment, OS3could switch to connect with

protectingﬁber, and the OS1of ONU could be turned on to connect to

the protectingﬁber. It is worth to mention that the operating of each ONUs will not be affected, since the downlink and video signals are still in broadcast mode and the uplink signal is still in TDM mode[2]. To realize the performance of the proposed self-protection TDM-PON system, an experiment is executed. The experimental setup is shown in

Fig. 1with four ONUs. The transmission length between OLT and each ONUs is 20 km, and the separation between two adjacent ONUs is 2 km. The 1490 and 1310 nm wavelengths are the downlink and uplink signals, using 2.5 and 1.25 Gb/s direct modulated signals respectively. They are modulated by non-return-to-zero (NRZ) data, with a pseudo random binary sequence (PRBS) pattern length of 231_{−1. In this measurement,}

the output powers of the downlink (Distributed Feedback laser) and the uplink (Fabry–Perot laser) signals are 2.2 and 2.4 dBm. For the case of 16 ONUs, in regard to the maximum power budget of the proposed PON scheme, the downlink and uplink signals would transmit through two WCs (~1.8 dB), two OSs (~2 dB), a 1×16 splitter (~12 dB), a 1×2 CP (~3 dB), and 22 kmfiber (~4.4 dB), respectively. Here, about b23 dB loss budget can be produced in the system.Fig. 5shows the bit error rate (BER) curves versus different received power under back-to-back (B2B), without and with protecting operation in Fig. 5. Negligible power penalties are observed at BER of 10−9 without and with the fiber protection. Besides, we can use the DFB-LD of ~5.5 dBm output power to solve the insufficient power budget in the proposed PON system, when the 1×16 splitter is replaced by 1×32 splitter. The inset ofFig. 5shows the restorable time of the proposed protection PON system is within 10 ms due to the switching limitation of optical switch. In the proposed PON Fig. 1. Proposed self-protection ring-star-architecture TDM-PON system without

fiber-fault occurring. S: 1 × N splitter; OS: optical switch; WC: WDM coupler; Tx: transmitter; Rx: receiver; MAC: medium access control; EDFA: erbium-dopedfiber amplifier.

Fig. 2. Proposed self-protected access network with an occurrence ofﬁber-fault between OLT and RN.

Fig. 3. Proposed self-protected access network with an occurrence ofﬁber-fault between RN and ONU1.

Fig. 4. Proposed self-protected access network with the occurrences of twoﬁber-faults between RN and ONU1and RN and ONU2.

3249 C.H. Yeh et al. / Optics Communications 284 (2011) 3248–3250

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system, the switching time depends on the optical switch (OS), which are used in the OLT and ONU. If one wants to reduce the switching time, we can employ the faster commercial optical switch for signal routing.

We use the standard CATV video signal broadcasting to each ONUs in the experiment. Actually, there are no any standards to determine whether the video signal can be allowed into each ONU. Thus, in order to manage the video service distribution to a large number of individual user, OS2is added in each ONU to control the video signal distribution in

optical layer, as shown inFig. 1. Initially, the OS2of all ONUs are in the

“on state” allowing to receive the video signal. If an ONUn does not want the video service, the OLT only give a message to MAC of ONUn for turning off the OS2to stop the service. The proposed management of

video service only requires the control of the OS2. It can reduce the

loading of MAC layer management.

To conﬁrm the proposed technology, the CATV signal having the operating bandwidth from 50 to 750 MHz with 6 MHz channel spacing is used in the proposed access network.Fig. 6(a) and (b) shows the output RF spectra of the CATV signal from 50 to 750 MHz after passing through 20 kmﬁber transmission when the OS2is turned on and off,

respectively. As also illustrated in Fig. 6(a), between 103.25 and 163.25 MHz, there is a gap-band that are reserved for other applications

according to the CATV standard. When the OS2is in“off state”, the CATV

channels could be isolated, as shown inFig. 6(b).

When multiple CATV channels are transmitted through a nonlinear device, such as an optical ampliﬁer, the composite second order (CSO) and composite triple beat (CTB) would be generated to effect and distort the video signal[9–11]. In addition, in this experiment we also measure the values of CNR, CSO and CTB under different NTSC channels from 83.25 MHz to 733.25 MHz in our proposed access network, as illustrated inFig. 7, when the CATV wavelength is 1550 nm at 7.6 dBm input power.

Fig. 7presents the maximum distorted values of CNR, CSO and CTB are 1.2, 1.8 and 4.3 dB at 181.24 MHz frequency band, respectively, after transmitting through our proposed PON system.

3. Conclusion

We proposed and demonstrated a novel new self-restored ring-star-architecture for TDM-PON with triple-play management in optical layer. Different scenarios of fiber-fault locations, e.g. in feeder and/or distributedfibers were analyzed. BER performance of data traffics in both uplink and downlink directions in the working and protecting modes were measured and studied. Standard CATV video signal distribution to each ONUs was also performed, showing the proposed network cannot only have self-restored function, but also can manage triple-play services in the optical layer.

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[11] C.C. Lee, S. Chi, IEEE Photon. Technol. Lett. 12 (2000) 341. Fig. 5. BER curves versus different received optical power for the 2.5 Gb/s downlink and

1.25 Gb/s uplink trafﬁc under the B2B, without and with protection status, respectively. Insert is the switching time of optical switch.

Fig. 7. Measured values of CNR, CSO and CTB under different NTSC channels from 83.25 MHz to 733.25 MHz.

Fig. 6. Output RF spectra of CATV signal from 50 to 750 MHz with 6 MHz channel spacing after through 20 kmﬁber transmission when the OS2 is turned (a) on and (b) off, respectively.