Optical Networking Technologies

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Outline

• Introduction to Fiber Optics• Passive Optical Network (PON) – point-to-point

fiber networks, typically to a home or small business

• SONET/SDH• DWDM (Long Haul)

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Optical Transmission

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OpticalFibre

Transmission System

OpticalFibre

Transmission System

electricalsignal

electricalsignal

opticalsignal

Advantages of optical transmission:1. Longer distance (noise resistance and less attenuation)2. Higher data rate (more bandwidth)3. Lower cost/bit

Optical Networks• Passive Optical Network (PON)– Fiber-to-the-home (FTTH)– Fiber-to-the-curb (FTTC)– Fiber-to-the-premise (FTTP)

• Metro Networks (SONET)– Metro access networks– Metro core networks

• Transport Networks (DWDM)– Long-haul networks

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Optical Network Architecture

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MetroNetwork

Long HaulNetwork

MetroNetwork

AccessNetwork

AccessNetwork

AccessNetwork

AccessNetwork

transport network

PON

SONET

DWDM

CPE (customer premise)

All-Optical Networks• Most optical networks today are EOE

(electrical/optical/electrical)• All optical means no electrical component

– To transport and switch packets photonically.

• Transport: no problem, been doing that for years• Label Switch

– Use wavelength to establish an on-demand end-to-end path

• Photonic switching: many patents, but how many products?

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Optical 101• Wavelength (): length of a wave and is measured in

nanometers, 10-9m (nm) – 400nm (violet) to 700nm (red) is visible light– Fiber optics primarily use 850, 1310, & 1550nm

• Frequency (f): measured in TeraHertz, 1012 (THz)• Speed of light = 3×108 m/sec

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Optical Spectrum

• Light– Ultraviolet (UV)– Visible– Infrared (IR)

• Communication wavelengths– 850, 1310, 1550 nm– Low-loss wavelengths

1550nm 193,548.4GHz

1551nm 193,424.6GHz

1nm 125 GHz

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UV IR

Visible

850 nm 1310 nm 1550 nm

125 GHz/nm

Bandwidth

Optical Fiber• An optical fiber is made of

three sections:– The core carries the

light signals– The cladding keeps the light

in the core– The coating protects the glass

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CladdingCore

Coating

Optical Fiber (cont.)

• Single-mode fiber– Carries light pulses by

laser along single path

• Multimode fiber– Many pulses of light

generated by LED travel at different angles

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SM: core=8.3 cladding=125 µmMM: core=50 or 62.5 cladding=125 µm

7.11

Bending of light ray

7.12

Figure 7.12 Propagation modes

7.13

Figure 7.13 Modes

7.14

Figure 7.14 Fiber construction

7.15

Figure 7.15 Fiber-optic cable connectors

7.16

Figure 7.16 Optical fiber performance

Note: loss is relatively flat

7.17

Fiber Installation

Support cable every 3 feet for indoor cable (5 feet for outdoor)

Don’t squeeze support straps too tight.

Pull cables by hand, no jerking, even hand pressure.

Avoid splices.

Make sure the fiber is dark when working with it.

Broken pieces of fiber VERY DANGEROUS!! Do not ingest!

Optical Transmission Effects

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AttenuationDispersion & Nonlinearity

Waveform After 1000 KmTransmitted Data Waveform

Distortion

Optical Transmission Effects

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Attenuation: Loss of transmission power due to long distance

Dispersion and Nonlinearities: Erodes clarity with distance and speed

Distortion due to signal detection and recovery

Transmission Degradation

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Loss of EnergyLoss of Energy

Loss of Timing (Jitter)Loss of Timing (Jitter)t t

Phase Variation

Shape DistortionShape Distortion

Ingress Signal Egress Signal

Optical Amplifier

Dispersion Compensation Unit (DCU)

Optical-Electrical-Optical (OEO) cross-connect

Passive Optical Network (PON)• Standard: ITU-T G.983• PON is used primarily in two markets: residential and

business for very high speed network access.• Passive: no electricity to power or maintain the

transmission facility.– PON is very active in sending and receiving optical signals

• The active parts are at both end points.– Splitter could be used, but is passive

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Passive Optical Network (PON)

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OLT: Optical Line Terminal ONT: Optical Network Terminal

Splitter(1:32)

PON – many flavors• ATM-based PON (APON) – The first Passive optical network

standard, primarily for business applications• Broadband PON (BPON) – the original PON standard (1995). It

used ATM as the bearer protocol, and operated at 155Mbps. It was later enhanced to 622Mbps.– ITU-T G.983

• Ethernet PON (EPON) – standard from IEEE Ethernet for the First Mile (EFM) group. It focuses on standardizing a 1.25 Gb/s symmetrical system for Ethernet transport only – IEEE 802.3ah (1.25G)– IEEE 802.3av (10G EPON)

• Gigabit PON (GPON) – offer high bit rate while enabling transport of multiple services, specifically data (IP/Ethernet) and voice (TDM) in their native formats, at an extremely high efficiency – ITU-T G.984

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xPON ComparisonBPON EPON GPON

Standard ITU-T G.983 IEEE 803.2ah ITU-T G.984

Bandwidth Down: 622MUp: 155M

Symmetric: 1.25G

Down: 2.5GUp: 2.5G

Downstream λ 1490 &1550 1550 1490 & 1550

Upstream λ 1310 1310 1310

Transmission ATM Ethernet ATM, TDM, Ethernet

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PON Case Study (BPON)

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Two Ethernet portsOne T1/E1 portOptical transport: 622M bps

PON (G.983)

ATM

AAL1 AAL5

CES

T1/E1

RFC2684

802.3

Optical Network Terminal (ONT)(customer premise)Optical Line Terminal (OLT)

(Central Office)

Packet Core(IPoATM)

TDM Core(PSTN)

SAR/CS

GPON

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EPON Evolution

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EPON Downstream

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EPON Upstream

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SONET in Metro Network

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Long Haul(DWDM)Network

Metro SONET Ring

Access Ring

Access Ring

Access Ring

ADMADMADMADM

ADMADM

ADMADM

ADMADM

ADMADMADMADM

Voice Switch

PBX

Core Router

T1

T1

IP Over SONET

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SONET

IP

????

SONET

IP

ATM

AAL5

RFC2684

802.3

SONET

IP

PPP

SONET

T1 DS3 OC-3

SONET is designed for TDM traffic, and today’s need is packet (IP) traffic. Is there a better way to carry packet traffic over SONET?

SONET

GFP

802.3

IP

GFP: Generic Frame ProcedureTDM Traffic

RFC1619

RFC 2684: Encapsulate IP packet over ATMRFC 1619: Encapsulate PPP over SONET

ATM over SONET (STS-3c)

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STS-3c Envelope

Cell 1 Cell 3Cell 2

9 rows

260 columns (octets)

Cell 1 Cell 2 Cell 3

OH

PPP over SONET• RFC 1619 (1994)• The basic rate for PPP over SONET is STS-3c at

155.520 Mbps.• The available information bandwidth is

149.760 Mbps, which is the STS-3c envelope with section, line and path overhead removed.

• Lower signal rates use the Virtual Tributary (VT) mechanism of SONET.

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PPP over SONET (STS-3c)

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STS-3c Envelope

PPP Frame 1 (HDLC) PPP Frame 3 (HDLC)

PPP Frame 1a

PPP Frame 2 (HDLC)

PPP Frame 1b PPP Frame 2a

PPP Frame 2b

PPP Frame 2c

PPP Frame 3 2d 9 rows

260 columns (octets)

POH

Path overhead

Dense Wave Division Multiplexing (DWDM)

Ref: Cisco DWDM Primer

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Continue Demands for More Bandwidth

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Faster Electronics(TDM)

Higher bit rate, same fiberElectronics more expensive

More FibersSame bit rate, more fibersSlow Time to MarketExpensive EngineeringLimited Rights of WayDuct Exhaust

WDM

Same fiber & bit rate, more sFiber CompatibilityFiber Capacity ReleaseFast Time to MarketLower Cost of OwnershipUtilizes existing TDM Equipment

TDM vs. WDM• Time division multiplexing

–Single wavelength per fiber–Multiple channels per fiber–4 OC-3 channels in OC-12–4 OC-12 channels in OC-48–16 OC-3 channels in OC-48

• Wave division multiplexing–Multiple wavelengths per fiber–4, 16, 32, 64 wavelengths per fiber–Multiple channels per wavelength

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Single Single Fiber (One Fiber (One

Wavelength)Wavelength)

Channel 1

Channel n

Single FiberSingle Fiber(Multiple (Multiple

Wavelengths)Wavelengths)

l1l1

l2l2

lnln

TDM vs. WDM• TDM (SONET/SDH)

–Take sync and async signals and multiplex them to a single higher optical bit rate–E/O or O/E/O conversion

• WDM–Take multiple optical signals and multiplex themonto a single fiber–No signal format conversion

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DS-1DS-3OC-1OC-3

OC-12OC-48

OC-12cOC-48c

OC-192c

FiberFiber

DWDMDWDMOADMOADM

SONETSONETADMADM

FiberFiber

FDM vs. WDM vs. DWDM• Is WDM also a Frequency Division Multiplexing (FDM) which has been

widely available for many years?• Short Answer: Yes. There is no difference between Wavelength Division

and Frequency Division. In general, FDM is used in the context of Radio Frequency (MHz – GHz) while WDM is used in the context of light ( THz)

• WDM: The original standard requires 100 GHz spacing to prevent signals interference.

• Dense WDM (DWDM): support multiplexing of up to 160 wavelengths of 10G/wavelength with 25GHz spacing– The use of sub 100GHz for spacing is called Dense WDM.– Some vendors even propose to use 12.5GHz spacing, and it would multiplex

up to 320 wavelengths

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Spectrum A Spectrum Bspacing

DWDM Economy

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TERMTERM

TERM

Conventional TDM Transmission—10 Gbps

1310RPTR

1310RPTR

1310RPTR

1310RPTR

1310RPTR

1310RPTR

1310RPTR

1310RPTR

TERM

40km

1310RPTR

1310RPTR

1310RPTR

1310RPTR

1310RPTR

1310RPTR

1310RPTR

1310RPTR

TERM1310RPTR

1310RPTR

1310RPTR

1310RPTR

1310RPTR

1310RPTR

1310RPTR

1310RPTR

TERM1310RPTR

1310RPTR

1310RPTR

1310RPTR

1310RPTR

1310RPTR

1310RPTR

1310RPTR

TERM

120 km

OC-48

OA OAOA OA120 km 120 km

OC-48OC-48

OC-48

OC-48OC-48

OC-48OC-48

DWDM Transmission—10 Gbps

1 Fiber Pair4 Optical Amplifiers

TERM

4 Fiber Pairs 32 Regenerators

40km 40km 40km 40km 40km 40km 40km 40km

Optical Transmission Bands

Band Wavelength (nm)

“New Band” 1360 – 1460

S-Band 1460 – 1530

C-Band 1530 – 1565

L-Band 1565 – 1625

U-Band 1625 – 1675

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DWDM: How does it work?TDM: multiple services onto a single

wavelength

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TDM

TDM

TDM

DWDM

Single pair of fiber strand Multiple wave lengths

DWDM Network

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MUX DEMUX

DWDM Network Components

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Optical Multiplexer

Optical De-multiplexerOptical Add/Drop Multiplexer

(OADM)

Transponder

1

2

3

1

2

3

15xx 1...n

1...n

ADMADM

Optical λ => DWDM λUsually do O-E-O

Optical Amplifier (OA)

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Pout Pin

EDFA (Erbium Doped Fiber Amplifier) amplifier

Separate amplifiers for C-band and L-band

gaingain

Optical ADM (OADM)• OADM is similar in many respects to SONET ADM, except that

only optical wavelengths are added and dropped, and there is no conversion of the signal from optical to electrical.

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Q: there is no framing of DWDM, so how do we add/drop/pass light?A: λ It is based on λ and λ only.

Cisco ONS 15800

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http://www.cisco.com/warp/public/cc/pd/si/on15800s/prodlit/ossri_ds.pdf

• TO build a long haul network • Up to 64 channels (i.e., wavelengths)• OC-12, OC-48, OC-192• up to 500 km

LEM: Line Extension Module

DWDM Network(point-to-point)

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OLA: Optical Line Amplifier

DWDM NetworkAdd-and-Drop

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Chicago Pittsburg New York

Note: this is a linear topology, and not a ring topology.

λ1: to Pittsburgλ2: to New York

λ1: dropλ2: pass

SONET and DWDM

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SONETChicago

SONETNew York

ADMADM ADMADM

DWDMterminal

DWDMterminal

Long Hall

ADMADM ADMADM

OC-3 OC-3

IP

PPP

SONET

IP

PPP

SONET

SONET

DWDMSONET

DWDM

IP over DWDM ???

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DWDMterminal

DWDMterminal

IP IPIP

DWDM

???

Note: There is no protocol called “IP over DWDM” or “PPP over DWDM”. However, there are many publications on “IP over DWDM” and they all require a layer-2 protocol which provides the framing to encapsulate IP packets. (see the previous slide)

Summary• Optical Fiber Network – the market needs• Access Network

– Passive Optical Network (PON)• Metro Network

– SONET/SDH• Transport Network (Long-Haul)

– DWDM• DWDM can be applied to metro and access networks as well, but unlikely for its high cost.

• Optical network is a layer-1 technology, and IP is a layer-3 protocol. There must be a layer-2 protocol to encapsulate IP packets to layer-2 framing before it goes to the optical layer– ATM (via RFC2684)– SONET (via PPP)– Ethernet (via GFP)

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