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

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

IntroductionChallenges 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

NGA: Options & ChallengesIEEE 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

Contd…Architecture of two optically amplified NGA options

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

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)

LROA architectures1. 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)

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

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.

Contd…• The SHRA-based LROA architecture supports a total number

of 128 users & maximum reach = 60 Km

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

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

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

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

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

Contd…• The deigns using MEMS mirrors & photonic crystals are

shown below:

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

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