This presentation is based on a paper on the issues in a Long Reach Passive Optical Network.

1. Presentation on
Challenges in next-generation optical
access networks: addressing reach
extension and security weaknesses
L.G. Kazovsky, S.-W. Wong, V. Gudla, P.T. Afshar, S.-H. Yen, S. Yamashita, Y. Yan
Presented by
Sourav Mondal

2. Abstract
• Recent trend in broadband optical access networks To deliver large
bandwidth to end users
• Operators mainly deploying TDM-PON in their networks
• TDM-PONs suffers from limited reach & split-ratio
• Also, to reduce CAPEX & OPEX COs must be consolidated
• Possible promising solution: LR-PON !!!
• LR-PON employ optical amplifiers to increase optical budget to support
longer reach and higher split-ratio
• More end users better security becomes an issue

3. Introduction
Challenges for LR-PON architecture:
• Amplified Spontaneous Emission (ASE) noise introduced by optical
amplifiers
• Burst-mode transmission in upstream
• Lack of suitable wide-band amplifiers
• Node management active cost
• Backward compatibility with TDM-PON
• Deployment of DWDM
• Lack of security measure to counter physical layer weaknesses

4. NGA: Options & Challenges
IEEE 802.3av 10G EPON (10 Gb/s TDM-PON)
• Downstream rate = 10 Gbps
• Upstream rate = 1.25, 2.5 or 10 Gbps, depending on Burst-
mode traffic
• FEC is recommended but, it reduces 12% throughput
ITU-T 984.5 and 984.6
• Similar features with more liberal in standard upgradation
• Defines wavelength enhancement: C/L band (1530-1625 mm)
• Reach extension: up to 60 Km
• Loss budget excess: 27.5 dB in both feeder & drop section

5. Contd…
Architecture of two optically amplified NGA options

6. Contd…
Wavelength Division Multiplexing (WDM)
• WDM exploits the large number of wavelengths available in the
fibre to potentially allow very high capacity
• WDM enables network operators to co-exist in an open-access
environment
• Major road-block: additional transceivers increased COST!
Reach extension (and higher split-ratio)
• The reach extension box must be able to overcome ASE and have
very short rise-time to support upstream burst-mode transmission
• Coarse wavelength division multiplexing (CWDM) a wide-band
amplifier becomes necessary
• Near–Far problem also means that the maximum round trip time
(RTT) could increase

7. Contd…
Higher rate or advanced modulation
• At rates 10 Gbps and beyond, NGA suffers from notable chromatic
dispersion impact
• Current burst-mode transceiver technology cannot adequately
support 10 Gbps upstream
• Advanced modulation techniques, such as, optical code division
multiple access (OCDMA) and optical orthogonal frequency
division multiplexing (optical OFDM) have also been considered
Security weaknesses
• PON is vulnerable to certain malicious attacks such as denial of
service
Hybrid Wireless Access
• Next-Gen wireless technologies: LTE and WiMax Backhaul
infrastructure is needed to be upgraded Radio over Fibre (RoF)

8. LROA architectures
1. TDM-based LROA architecture: superPON
• Use of Optical Amplifiers extended physical reach beyond 100 Km
• The SuperPON architectures rely on three stages of Remote
Amplification Units (RAU)

9. Contd…
• As shown in figure, the final two stages of the RAUs connect
to a 1:32 and 1:64 splits, respectively. The total number of
split-ratio in SuperPON is 2048
• Downlink: Erbium Doped Fibre Amplifier (EDFA) is used
it is cost effective and has high performance
• Uplink: Semiconductor Optical Amplifier (SOA) is used
because EDFA cannot support fast upstream burst-mode
transmission. SOA is also compact and low cost compared to
Raman amplifier
• A recent variant of SuperPON architecture supports a
maximum distance of 135 km and proposes downstream
transmission of 10 Gb/s with a DWDM implementation that
supports over 40 wavelengths

10. Contd…
2. CWDM-based LROA architecture: hybrid wide-band
amplifiers
• DWDM leads to heating of Lasers TDM-PONs doesn’t
have coolers to reduce cost
• CWDM systems can support multiple wavelengths without
requiring Laser cooling at ONU
• Challenge: current amplifiers cannot achieve high BW needed
for CWDM
• Solution: proposal for SOA Raman Hybrid Amplifier (SHRA)
• The SRHA had a gain peak at 1525 nm which allowed the use
of the amplifier for both C and L bands.

11. Contd…
• The SHRA-based LROA architecture supports a total number
of 128 users & maximum reach = 60 Km

12. Security measures in current generation
TDM-PON architectures
Main reasons for security attack:
• The ONUs share an open and physically broadcast medium in
the downstream
• There are very limited resources for operators to learn or
counter network failures because the network is completely
passive in the field
1. Eavesdropping:
• Protection required any ONU can listen to data sent to other
ONUs
• Uplink may not be secure malicious user may use sensitive
receiver to eavesdrop on the signal reflected from PS

13. Contd…
2. Denial of Service (DoS) attack:
• A malfunctioning (babbling) or purposefully malicious ONU
sends in-band signal that blocks some or the entire ONU
upstream traffic
3. Masquerade (spoofing attack) or replay attack
• Malicious ONU user can listen and decrypt traffic of another
ONU user malicious ONU can easily steal the identity of
the victimised ONU to disguise and masquerade as the
victimised ONU
• Even if not decrypted, it can relay the collected signals & may
cause disturbance

14. Contd…
Optical monitoring and detection
1. OTDR monitoring sub-systems
• OTDR measures the fibre losses based the strength of the return
pulse and can detect irregular actions
2. Detection technique based on loopback modulation
• Each ONU device is given a unique, fixed PN signature associated
with its hardware
• When a malicious DoS user attack occurs OLT could activate the
loop-back tester, which sends a test command sequentially to each
ONUs to identify the source of disturbance
3. Optical power monitoring sub-systems
• Optical power monitoring techniques can directly observe the
activities of the active signals

15. Contd…
Attack counter-measure methods
1. Active switching
• Active optical switches can be used to implement protection switching.
2. Passive fuse
• The proposed sub-system uses specialty fibre that is concatenated with carbon-
coated TeO2 segments to make it susceptible to high laser power the system
optically burns the fuse to expel troubling users from the network

16. Remote node architecture for LROA
and security enhancement
QPAR and multi-stage latching device
• It is possible to use multimode interference(MMI) or a variant of split-and-
delivery switch to provide variable power splitting
• QPAR power splitter should perform the exact same function of a variable
power splitter but latch in stable states

17. Contd…
• The deigns using MEMS mirrors & photonic crystals are
shown below:

18. Results of simulation
• The reach experiments simulate a PON network with fixed
optical budget and uniformly random user distribution between
5 and 60 km
• MZI-RN conserves power to the near users and is able to
support 40–175% more users

19. Conclusion
• LROA networks are promising solutions that can
simultaneously serve larger bandwidth while supporting longer
reach and higher split-ratio in the distribution network.
• LROA architectures employ optical amplifier technology and
actively extend the optical budget
• The review summarises architectures and enabling
technologies that overcome ASE, burst-mode transmission in
the upstream, wide-band amplifiers and wavelength drift
owing to temperature variations
• A novel class of reconfigurable devices based on Mach–
Zhender interferometer and latchable optics has been
introduced to address security weaknesses, which are suitable
under LROA architectures