TTM1 – 2013: Core networks and Optical Circuit Switching (OCS)

Overview topics

● Short repetition of two important facts● Optical networks (Zouganeli)● CWDM and DWDM networking (TransPacket

white-paper)● Switching architectures (Borella)

Short repetition of two important facts (1)

11 11

11 1111 1144 44

11

22

33

44

11

22

33

44

Tidligere utbygging

RegeneratorTerminalFiber

Før: 1 kanal pr fiber

Optiskforsterker

MultiplekserDemultiplekser

2,5 Gb/s =30000

Opptil20 000 000

WDM: 4-128 kanaler

pr fiberNåværende utbygging

Wavelength Division Multiplexing(WDM), mangedobler kapasitet i fiber

Electronic/electrooptical

Now

Optical amplifier

WDM: 4-128 channelspr fiber

1 channel pr fiber

Up to

Earlier

WDM increases capacityOptical amplifiers simplifies the system

Short repetition of two important facts (2)

Optisk krysskopler

BølgelengdeKonverter

I1

I2

I3

I4

U1

U2

U3

U4Wavelengthconverter

Optical crossconnect

Cross-connection of wavelengths and blocking:Signals inserted into a fibre must be of different wavelengths.

Optical networks (Zouganeli)

● Increased traffic demands (e.g. from broadband home users/businesses and new services) => Fat pipes needed.

● ”IP everywhere” and development in optical technology => Fokus on simplifications:

Network element functionality (1)● 70 % of traffic is through-passing in typical node

=> Should be able to avoid processing of this traffic.● Simple optical network element

– Static Optical Add-Drop Multiplexer (here: ring network):

● Fixed wavelengths dropped and added at each node.

● Not reconfigurable (inaccessible to control system).

Course WDM● Cheaper technology with less scalability than DWDM● Typically maximum 16 channels

0

0,1

0,2

0,3

0,4

0,5

1200 1300 1400 1500 1600

Wavelength (nm)

Lo

ss (

dB

/km

)

2 dB/km

G.652G.652C

1271-1451 nm 1471-1611 nm

16 channel CWDM using two multiplexers for two different bands

8

EXT EXT

C1 – (8+1) C1– (8+1)

C1 – 8L C1 – 8L

14711491151115311551157115911611

14711491151115311551157115911611

12711291131113311351137114311451

12711291131113311351137114311451

CWDM and DWDM hybrid

C1-8

D1-52 D1-52

14711491151115311551157115911611

C1–8

1535.82 1535.04 1534.25 1533.47 1532.68 1531.90 1531.12

1530.33

14711491151115311551157115911611

1535.82 1535.04 1534.25 1533.47 1532.68 1531.90 1531.12

1530.33

Network element functionality (2)● Traffic bypassing

intermediate IP routers => Less load on routers (can be smaller and cheaper)

● In meshed networks:Used to directly connect node pairs with high traffic between them.

● (UNINETT is in the process of doing this now).

Reconfigurable (R-)OADM● A flexible add-drop function● Use cross-connect for some wavelength/wavebands

Not singlewavelength!

Alternative R-OADM switch implementations

Opaque vs. transparent● Transparent:

All-optical transport independent of:- data rate (within limits)- protocols and formats

● Opaque: OEO conversion, i.e. signal received/interpreted by electronic receiver/logic– Expected to follow certain

speeds/formats.

Needed functionality for optical OXC based networks (1)

● Opto-electronic or all-optical.● Scalability and flexibility

– Handles much higher number of line ports and directions than R-OADM– Higher flexibility than R-OADM

● Service provisioning: End-to-end lightpaths should be provisioned in an automated fashion (not necessarily all-optical or same wavelength end-to-end).

● Protection and restoration: Must have mechanisms to protect against fiber cuts or equipment failure at nodes. I.e. redirect traffic from failed to backup paths.

● Wavelength conversion: Lightpaths can change wavelength to increase flexibility in allocating network resources. Much easier to implement in opto-electronic OXC than in all-optical OXC;3R versus 2R (Mach-Zhender interferometer).

● Multiplexing and grooming: Normally done in the opto-electronical add-drop part.

● Today mainly opto-electronic solutions.● Many candidate all-optical solutions:

- Generic switch architectures (Clos, Shuffle,..) where elements are simple optical switch elements, connected with fibers. - ”Broadcast and select” switching matrixes realized with splitters and Semiconductor Optical Amplifiers (SOAs) (0 – 1 : block or let-through light).- Two- or three dimensional array of micro mirrors (MEMS)- Tunable wavelength converters and Array Waveguide Gratings (AWG)

Needed functionality for optical OXC based networks (2)

Transparent (all-optical) switches (1)

● Micro-electro-machining systems (MEMS)

● Complicated, but has received a lot of attention.

● Similar production techniques as for electronic chips

Transparent (all-optical) switches (2)

● Currently widely discussed in research literature

● However: Tunable Wavelength Converters (TWCs) are very expensive.

Potential future IP router architecture● Aggregation in

IP/MPLS switch part

● Cross-connection of wavelengths at optical layer– Tunable lasers

Switching architectures with wavelength conversion (Borella)

● Dedicated converters for each output – Many converters– Flexible, no blocking– Wavelength specific multiplexers minimizes

attenuation.

Switches with shared wavelength conversion

● Shared between all input lines– Access from any input wavelength– Optimal wavelength converter resource utilization– WC may not be available if too few– Extra switch between WC and output MUX

required.

Wavelength converters shared for input fibre

● Less efficient utilization of WC pool than fully shared ● Larger probability for blocking with the same number of

WC’s ● Extra switch not required, i.e. simpler design

Switch with add/drop and shared wavelength conversion

● If electronic conversion then not transparent– Transparent usually means transparent to bitrate– Other types of transparency?