optical networking overview

1. Optical Networking
Technologies
1

2. 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)
2

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

4. 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
4

5. Optical Network Architecture
5
Metro
Network
Long Haul
Network
Metro
Network
Access
Network
Access
Network
Access
Network
Access
Network
transport network
PON
SONET
DWDM
CPE (customer premise)

6. 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?
6

7. Optical 101
• Wavelength (λ): length of a wave and is measured in
nanometers, 10-9
m (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
7

8. 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
8
UV IR
Visible
850 nm 1310 nm 1550 nm
λ
125 GHz/nm
Bandwidth

9. 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
9
CladdingCore
Coating

10. 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
10
SM: core=8.3 cladding=125 µm
MM: core=50 or 62.5 cladding=125 µm

11. 7.11
Bending of light ray

12. 7.12
Figure 7.12 Propagation modes

13. 7.13
Figure 7.13 Modes

14. 7.14
Figure 7.14 Fiber construction

15. 7.15
Figure 7.15 Fiber-optic cable connectors

16. 7.16
Figure 7.16 Optical fiber performance
Note: loss is relatively flat

17. 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!

18. Optical Transmission Effects
18
Attenuation
Dispersion & Nonlinearity
Waveform After 1000 KmTransmitted Data Waveform
Distortion

19. Optical Transmission Effects
19
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

20. Transmission Degradation
20
Loss of Energy
Loss of Timing (Jitter)
t t
Phase Variation
Shape Distortion
Ingress Signal Egress Signal
Optical Amplifier
Dispersion Compensation Unit (DCU)
Optical-Electrical-Optical (OEO) cross-connect

21. 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
21

22. Passive Optical Network (PON)
22
OLT: Optical Line Terminal
ONT: Optical Network Terminal
Splitter
(1:32)

23. 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
23

24. xPON Comparison
BPON EPON GPON
Standard ITU-T G.983 IEEE 803.2ah ITU-T G.984
Bandwidth Down: 622M
Up: 155M
Symmetric:
1.25G
Down: 2.5G
Up: 2.5G
Downstream λ 1490 &1550 1550 1490 & 1550
Upstream λ 1310 1310 1310
Transmission ATM Ethernet ATM, TDM,
Ethernet
24

25. PON Case Study (BPON)
25
Two Ethernet ports
One T1/E1 port
Optical 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

26. GPON
26

27. 27
EPON Evolution

28. 28

29. 29

30. 30

31. EPON Downstream
31

32. EPON Upstream
32

33. SONET in Metro Network
33
Long Haul
(DWDM)
Network
Metro SONET Ring
Access Ring
Access Ring
Access Ring
ADMADM
ADMADM
ADMADM
ADMADM
ADMADM
ADMADMADMADM
Voice Switch
PBX
Core Router
T1
T1

34. IP Over SONET
34
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 ATM
RFC 1619: Encapsulate PPP over SONET

35. ATM over SONET (STS-3c)
35
STS-3c Envelope
Cell 1 Cell 3Cell 2
9 rows
260 columns (octets)
Cell 1 Cell 2 Cell 3
OH

36. 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.
36

37. PPP over SONET (STS-3c)
37
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 32d 9 rows
260 columns (octets)
POH
Path overhead

38. Dense Wave Division
Multiplexing (DWDM)
Ref: Cisco DWDM Primer
38

39. Continue Demands for More Bandwidth
39
Faster Electronics
(TDM)
Higher bit rate, same fiber
Electronics more expensive
More Fibers
Same bit rate, more fibers
Slow Time to Market
Expensive Engineering
Limited Rights of Way
Duct Exhaust
W
D
M
Same fiber & bit rate, more λs
Fiber Compatibility
Fiber Capacity Release
Fast Time to Market
Lower Cost of Ownership
Utilizes existing TDM Equipment

40. 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
40
SingleSingle
Fiber (OneFiber (One
Wavelength)Wavelength)
Channel 1
Channel n
Single FiberSingle Fiber
(Multiple(Multiple
Wavelengths)Wavelengths)
l1l1
l2l2
lnln

41. 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 them
onto a single fiber
–No signal format conversion
41
DS-1
DS-3
OC-1
OC-3
OC-12
OC-48
OC-12c
OC-48c
OC-192c
FiberFiber
DWDMDWDM
OADMOADM
SONETSONET
ADMADM
FiberFiber

42. 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
42
Spectrum A Spectrum Bspacing

43. DWDM Economy
43
TERM
TERM
TERM
Conventional TDM Transmission—10 Gbps
1310
RPTR
1310
RPTR
1310
RPTR
1310
RPTR
1310
RPTR
1310
RPTR
1310
RPTR
1310
RPTR
TERM
40km
1310
RPTR
1310
RPTR
1310
RPTR
1310
RPTR
1310
RPTR
1310
RPTR
1310
RPTR
1310
RPTR
TERM
1310
RPTR
1310
RPTR
1310
RPTR
1310
RPTR
1310
RPTR
1310
RPTR
1310
RPTR
1310
RPTR
TERM
1310
RPTR
1310
RPTR
1310
RPTR
1310
RPTR
1310
RPTR
1310
RPTR
1310
RPTR
1310
RPTR
TERM
120 km
OC-48
OA OAOA OA
120 km 120 km
OC-48
OC-48
OC-48
OC-48
OC-48
OC-48
OC-48
DWDM Transmission—10 Gbps
1 Fiber Pair
4 Optical Amplifiers
TERM
4 Fiber Pairs
32 Regenerators
40km 40km 40km 40km 40km 40km 40km 40km

44. 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
44

45. DWDM: How does it work?
TDM: multiple services onto a single
wavelength
45
TDM
TDM
TDM
DWDM
Single pair of fiber strand
Multiple wave lengths

46. DWDM Network
46
MUX DEMUX

47. DWDM Network Components
47
Optical Multiplexer
Optical De-multiplexer
Optical Add/Drop Multiplexer
(OADM)
Transponder
λ1
λ2
λ3
λ1
λ2
λ3
850/1310 15xx λ1...n
λ1...n
ADMADM
Optical λ => DWDM λ
Usually do O-E-O

48. Optical Amplifier (OA)
48
PoutPin
 EDFA (Erbium Doped Fiber Amplifier) amplifier
 Separate amplifiers for C-band and L-band
gain

49. 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.
49
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.

50. Cisco ONS 15800
50
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

51. DWDM Network
(point-to-point)
51
OLA: Optical Line Amplifier

52. DWDM Network
Add-and-Drop
52
Chicago Pittsburg New York
Note: this is a linear topology, and not a ring topology.
λ1: to Pittsburg
λ2: to New York
λ1: drop
λ2: pass

53. SONET and DWDM
53
SONET
Chicago
SONET
New York
ADMADM ADMADM
DWDM
terminal
DWDM
terminal
Long Hall
ADMADM ADMADM
OC-3 OC-3
IP
PPP
SONET
IP
PPP
SONET
SONET
DWDM
SONET
DWDM

54. IP over DWDM ???
54
DWDM
terminal
DWDM
terminal
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)

55. 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)
55