Optical Transport Technologies and Trends

Optical Transport Technologies and Trends

August 20, 2015

Dion Leung, Director of Solutions and Sales Engineering

[email protected]

Company Confidential BTI Systems. Distribution of this document is not permitted without written authorization. 2

§ Logical connectivity is presented between the routers/switches

§ The underlying “physical” network is an abstract layer

§ One often requires to know if the routers have 10G, 40G, 100G interfaces and how many of these interfaces are available

In Data/Packet Networking World…

P P

PEPECE

CE


§ To engineer an optical transmission network, one would need to know EXACTLY the underlying fiber topology, the fiber details and characteristics, so that the optical layer can be designed accordingly.

§ Economics of regional network <> metro network <> ULH network

In Optical Transport Networking World…

DWDM

40kmDWDM

30km

CE

DWDM

DWDM

DWDM

CE

14km

35km

10km

15km35km


§ Technology Enabler: Wavelength Division Multiplexing – A transmission technology that multiplexes multiple optical carrier signals on a single fiber by using different wavelengths (colors) of laser light to carry different signals of frequencies.

– Frequency (in THz) and wavelength (in nm) are often used to label a wavelength and the frequency of a signal is inversely proportional to wavelength. e.g. 193 x 1012 THz or 1551.9 nm

Wavelength Division Multiplexing (WDM) –Similar to Sharing Spectrum over Air, Except Medium here is Fiber

MUX

Individually Colored Wavelengths

DEMUX

Single Transmission Fiber

Individually Colored Wavelengths

Equally spaced channels (aka standard ITU grid)


§ Optical light transmitted through fiber will lose power

§ Attenuation caused by Scattering, Absorption and Stress

§ Other related parameter: fiber length, fiber type, transmission bands, and external loss components such as connectors & splices

§ Typical fiber loss: 0.20 dB/km – 0.35 dB/km, although in some regions fiber loss can be as high as ~0.5 dB/km

§ Basic Link Budget Engineering:– Fiber loss + spice loss + connector loss + safety margin ≤ Power Budget (i.e. Transmitted – Received Power)

Fiber Characteristic #1:Fiber Attenuation or Loss (measured in dB or dB/km)


Transmission Windows:Attenuation in Optical Fiber (measured in dB or dB/km)

800 900 1000 1100 1200 1300 1400 1500 1600

Wavelength in nanometers (nm)

0.2 dB/km

0.5 dB/km

2.0 dB/km

C-band (1530 –1565 nm)

L-band (1565 –1625 nm)

Note: Frequency = 3 x 108 / wavelength

850 nm Range

1310 nm Range

Also known as the three “Transmission” Windows


§ Different wavelengths travel at different speeds through a given fiber causing optical pulses to broaden or to “spread”

– e.g. Wavelength Channel #1 travels faster than Channels #2, #3, etc..

§ Excessive spread can cause pulses to overlap, and therefore receivers would have a hard time to distinguish overlapped pulses

§ The longer the distance (or the higher the bitrate) is, the worst the spread would be.

Fiber Characteristic #2:Chromatic Dispersion (measured in ps / km-nm)


Lego Blocks of a Simple Point to Point DWDM System

TransponderMuxponderTransceiver

MuxDemux


§ Multiplex / Demultiplexer (aka. Mux/Demux) Comes with Various Sizes…– Use light’s reflection and refraction properties to separate and combine wavelengths from a

fiber strand (e.g. logically think of a prism)

– Common technologies: thin film filters, fiber bragg gratings and arrayed waveguides (AWG)

– Passive device which requires no power

– Higher the channel counts means higher the insertion loss

Lego Block to Create the Highway Lanes Common Mux/Demux Selections from most vendors…

DWDM Mux-Demux (8λ Add-Drop)

CWDM Mux-Demux (4λ Add-Drop)

OADMs (1,2, and 4λ Add-Drop)




Transponder and Muxponders:Converting “Grey” to “Color”

Transponder

Muxponder

Client Signal (Grey optics) (e.g. from a switch, router)

Line Signal (Color optics)(to DWDM mux / outside plant)

10GE LAN PHY(STM64, 10G FC)

a 10G Wavelength(e.g. Channel 3)

a 10G Wavelength(e.g. Channel 4)

GbESTM162G FC

STM4GbE

1 in – 1 out

Many in – 1 out


Transceivers

§ Typical Line Rates

– 2.5G

– 10G

– 100G

§ Transceivers

– SFP

– XFP/SFP+

– QSFP+

– CFP

§ Selection of which type mainly depends on Speed, Reach– 850nm, 1310nm, 1550nm, CWDM, DWDM Fixed Channel, DWDM Tunable

§ Each type of transceiver’s has its transmit power and receive power sensitivity(e.g. TX = [-3,1] dBm, RX = [-25, -5] dBm) à Max Budget = 1-(-25) = 26dB

Optical Transceivers – The Pluggable Optics


Additional Lego Blocks of Multi-Node Linear DWDM System

TransponderMuxponderTransceiver

MuxDemux

OpticalAmplifier

DispersionCompensation


Overcome Fiber Attenuation… Optical Amplifiers (EDFA and Raman)

Optical Amplifiers are Needed in Order to be Sure Optical Signals Can Be Accurately Detected by Receivers

Two Common Types of Optical Amplifiers

Erbium Doped Fiber Amplifier RAMAN Amplifier

Most common used and simple to deploy

Fixed gain or Variable gain

For high span loss and long distance transmission

Used in Conjunction With EDFAs


End End

0

Max

Min

Receiver

ToleranceCD

Dispersion Compensation Over Multi-span Route(Note: for 100G coherent transmission, CD is less of an issue…)

DCM DCM DCM

Span-by-Span CD Compensation for 10G/40G transmission

Simply match fiber distance to DCM type (e.g. Use 60km DCM for ~60km link)


As Network Grows and Evolves to Ring / Mesh Topologies…Advanced Technology Enabler Makes Operation & Planning Simpler

From www.datacentermap.com


§ For initial Point-to-Point network, Fixed OADM (FOADM) network architecture worked fine.

§ A problem arises when we have intermediate location that requires “partial” adding/dropping of traffic à manual patch work is needed

Unexpected Network Expansion or Node InsertionWavelength power management can become tricky to engineer

A C

40km

10dB

B

20km

5dB

§ 10 x 10GbE circuits are now between Site A and Site B

§ 10 x 10GbE circuits are now between Site A and Site C (via Site B)

10 x 10GbE10 x 10GbE


§ Since not all wavelengths need to be dropped, manual padding, patching works are required to connect wavelength across intermediate site(s)

§ Patching through makes sense for small λ counts, but with 40/96 DWDM channels, this can be prone to human errors and difficult to manage –a better solution is warranted.

A Closer Look: Channel Patching Work is RequiredIntermediate Site (at Site B)

DEMUX M

UXλ

λ

λ

λ

λ

λ

λ

λ

λλ

1. The insertion lossaffects the overall link budget

2. Each wavelength addedneeds to be re-balanced

λ 3. Regeneration is oftenneeded due to deficit power budget

From Site A At Site B To Site C


How a 4-Degree ROADM Node Works…

A/DEx2

Ex4

Ex3

ROADM

FiberLine

A/D

Ex3

Ex2

Ex4

ROADM

FiberLine

A/D

Ex2

Ex4

Ex3

ROADM

FiberLine

λ

Mux / Demux

λ

λ A/D

ROADM

FiberLine

Ex2

Ex3

Ex4

Mux / Demux

λ

λA Single ExpressCable

AutomaticPowerEqualizedWavelengths

In-Service Network Expansion by SimplyAdding ROADM module


Network-wide Benefit of ROADM: Reconfigurability, Flexibility and Ease of Expansion

• Individual wavelengths can be easily steered from any node to any node

• Site visit only at the add/drop locations• Simplify operations and network planning

OO

O

OO

O


Optical LayerLego Block

Uses & Benefits Additional Design Notes

Fiber Pair For DWDM transmission • G.652 / SMF is preferred

Mux / Demux (M/D) For dividing fiber into virtual highway lanes or wavelengthchannels

• Passive element (no power required)

• Various M/D have different insertion loss

DispersionCompensation Fiber or Module (DCF/DCM)

For compensation CD for80km or longer span or multi-span network

• DCF is usually classified by distance

• DCF has insertion loss and add latency

Amplifier For overcoming fiber span loss and minimizing regeneration cost for multi-span network

• Choice of EDFA (commonly used metro) and Raman (for regional/long-haul)

• Amplifier has various gain levels, noise figure

ReconfigurableOptical Add/Drop Multiplexer(ROADM)

For flexible wavelength add/drop/bypass and simpler operation

• Single module combines amplifier and WSS

• Per-channel auto power balancing

Summary of Essential Lego Blocks for Building a Flexible Optical Network


DWDM

40kmDWDM

30km

CE

DWDM

DWDM

DWDM

CE

14km

35km

10km

15km35km

§ One school of thought: Router vendors have integrated DWDM or color optical interfaces onto their routing platform

§ Another school of thought: Optical vendors have integrated packet functionalities (L2/L3) onto their optical platform

§ Which option is better? Which option is more cost effective? It depends.

Remember this View?

P P

PEPECE


School of Thought #1… Simple Point to PointConverged Packet Optical Networking

EdgeRouter

Core Router

Core Router

§ Optics on routers simplify the need for a separate optical platform§ Limited to point-to-point or simple fiber topology. Remember the

fundamental optical rules and lego blocks don’t disappear.

§ Optical reach depends on the integrated optical transceiver specifications§ 100G coherent technology helps overcome dispersions

Integrated Optics on Routers

EdgeRouter


School of Thought #2… Beyond Point to PointConverged Packet Optical Networking

NMSEdgeRouter

Core Router

Core Router

§ Pre-integrated solution using 10G/100G colored interfaces from existing feature-rich routing platform, or grey optics handoff

§ ROADM layer can provide additional layer of flexibility at physical layer

§ OSS/NMS integration can simplify operations and troubleshooting

Dynamic ROADM Core

EdgeRouter


School of Thought #3… DC+C Provider CentricConverged Packet Optical Networking

• If many Layer 3 features go unused in routers, you paid for them anyway• If most of Layer 3 traffic is actually MPLS LSR switching…• MPLS LER features are higher cost than simple LSR • Do you use all the RFC’s and functionalities in your routers today?• MPLS LER and LSR functions do not need to be on same equipment

LER

WDM

LER/LSR

$$$$$

LER

WDM

LSR

$$

LER$$ $$

$

LER

WDM+LSR

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Optical Transport Technologies and Trends

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