Transcript Optical network technology

Optical Networking
Technologies
1
Outline
• Introduction to Fiber Optics
• Passive Optical Network (PON) – point-topoint fiber networks, typically to a home
or small business
• SONET/SDH
• DWDM (Long Haul)
2
Optical Transmission
electrical
signal
Optical
Fibre
Transmission
System
optical
signal
Optical
Fibre
Transmission
System
electrical
signal
Advantages of optical transmission:
1. Longer distance (noise resistance and less attenuation)
2. Higher data rate (more bandwidth)
3. Lower cost/bit
3
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
Optical Network Architecture
DWDM
SONET
Long Haul
Network
Metro
Network
transport network
Metro
Network
PON
Access
Network
Access
Network
Access
Network
Access
Network
CPE (customer premise)
5
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
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

IR
UV
125 GHz/nm
Visible
850 nm
1550 nm
1310 nm
• Light
Bandwidth
– Ultraviolet (UV)
– Visible
– Infrared (IR)
• Communication wavelengths
– 850, 1310, 1550 nm
1550nm
193,548.4GHz
1551nm
193,424.6GHz
1nm
125 GHz
– Low-loss wavelengths
8
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
Core
Cladding
Coating
9
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
SM: core=8.3 cladding=125 µm
MM: core=50 or 62.5 cladding=125 µm
10
Bending of light ray
7.11
Figure 7.12 Propagation modes
7.12
Figure 7.13 Modes
7.13
Figure 7.14 Fiber construction
7.14
Figure 7.15 Fiber-optic cable connectors
7.15
Figure 7.16 Optical fiber performance
7.16
Note: loss is relatively flat
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!
7.17
Optical Transmission Effects
Attenuation
Dispersion & Nonlinearity
Distortion
Transmitted Data Waveform
Waveform After 1000 Km
18
Optical Transmission Effects
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
19
Transmission Degradation
Ingress Signal
Egress Signal
Loss of Energy
Optical Amplifier
Shape Distortion
Dispersion Compensation Unit (DCU)
Loss of Timing (Jitter)
t
Phase Variation
t
Optical-Electrical-Optical (OEO) cross-connect
20
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)
OLT: Optical Line Terminal
ONT: Optical Network Terminal
Splitter
(1:32)
22
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
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
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PON Case Study (BPON)
Optical Line Terminal (OLT)
(Central Office)
Packet Core
(IPoATM)
Optical Network Terminal (ONT)
(customer premise)
Two Ethernet ports
One T1/E1 port
Optical transport: 622M bps
T1/E1
802.3
CES
RFC2684
AAL1
AAL5
SAR/CS
ATM
TDM Core
(PSTN)
PON (G.983)
25
GPON
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EPON Evolution
27
28
29
30
EPON Downstream
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EPON Upstream
32
SONET in Metro Network
Long Haul
(DWDM)
Network
Core Router
ADM
ADM
Metro SONET Ring
Voice Switch
ADM
ADM
ADM
Access Ring
Access Ring
T1
ADM
Access Ring
ADM
T1
PBX
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IP Over SONET
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?
T1
DS3
OC-3
IP
IP
????
SONET
TDM Traffic
SONET
802.3
RFC2684
IP
IP
AAL5
PPP
802.3
ATM
RFC1619
GFP
SONET
SONET
SONET
GFP: Generic Frame Procedure
RFC 2684: Encapsulate IP packet over ATM
RFC 1619: Encapsulate PPP over SONET
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ATM over SONET (STS-3c)
Cell 1
Cell 2
Cell 3
260 columns (octets)
Cell 1
Cell 2
Cell 3
OH
9 rows
STS-3c Envelope
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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)
PPP Frame 1 (HDLC)
PPP Frame 2 (HDLC)
PPP Frame 3 (HDLC)
260 columns (octets)
PPP Frame 1a
PPP Frame 2a
PPP Frame 1b
PPP Frame 2b
POH
PPP Frame 2c
2d
Path overhead
9 rows
PPP Frame 3
STS-3c Envelope
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Dense Wave Division
Multiplexing (DWDM)
Ref: Cisco DWDM Primer
38
Continue Demands for More Bandwidth
Same bit rate, more fibers
Slow Time to Market
Expensive Engineering
Limited Rights of Way
Duct Exhaust
More Fibers
W
D
M
Faster Electronics
(TDM)
Same fiber & bit rate, more s
Fiber Compatibility
Fiber Capacity Release
Fast Time to Market
Lower Cost of Ownership
Utilizes existing TDM Equipment
Higher bit rate, same fiber
Electronics more expensive
39
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
Channel 1
Single
Fiber (One
Wavelength)
Channel n
• Wave division multiplexing
–Multiple wavelengths per fiber
–4, 16, 32, 64 wavelengths per fiber
–Multiple channels per wavelength
l1
l2
Single Fiber
(Multiple
Wavelengths)
ln
40
TDM vs. WDM
• TDM (SONET/SDH)
DS-1
–Take sync and async signals
DS-3
and multiplex them to a single OC-1
higher optical bit rate
OC-3
OC-12
–E/O or O/E/O conversion
SONET
ADM
Fiber
OC-48
• WDM
–Take multiple optical
signals and multiplex them OC-12c
OC-48c
onto a single fiber
OC-192c
–No signal format conversion
DWDM
OADM
Fiber
41
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
Spectrum A
spacing
Spectrum B
42
DWDM Economy
Conventional TDM Transmission—10 Gbps
40km 40km 40km 40km 40km 40km 40km 40km 40km
1310
1310
1310
1310
1310
1310
1310
1310
TERM
TERM
RPTR
1310
RPTR
1310
RPTR
1310
RPTR
1310
RPTR
1310
RPTR
1310
RPTR
1310
RPTR
1310
TERM
TERM
RPTR
1310
RPTR
1310
RPTR
1310
RPTR
1310
RPTR
1310
RPTR
1310
RPTR
1310
RPTR
1310
TERM
TERM
RPTR
1310
RPTR
1310
RPTR
1310
RPTR
1310
RPTR
1310
RPTR
1310
RPTR
1310
RPTR
1310
TERM
TERM
RPTR
RPTR
RPTR
RPTR
RPTR
RPTR
RPTR
RPTR
DWDM Transmission—10 Gbps
OC-48
OC-48
OC-48
OC-48
120 km
120 km
OA
OA
4 Fiber Pairs
32 Regenerators
OC-48
OC-48
OC-48
OC-48
120 km
OA
OA
1 Fiber Pair
4 Optical Amplifiers
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Optical Transmission Bands
Band
“New Band”
S-Band
C-Band
L-Band
U-Band
Wavelength (nm)
1360
1460
1530
1565
1625
–
–
–
–
–
1460
1530
1565
1625
1675
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DWDM: How does it work?
TDM: multiple services onto a single
wavelength
TDM
DWDM
TDM
TDM
Single pair of fiber strand
Multiple wave lengths
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DWDM Network
MUX
DEMUX
46
DWDM Network Components
1
850/1310
15xx
1...n
2
3
Transponder
Optical λ => DWDM λ
Usually do O-E-O
Optical Multiplexer
1
2
1...n
3
ADM
Optical De-multiplexer
Optical Add/Drop Multiplexer
(OADM)
47
Optical Amplifier (OA)
Pin
gain
Pout

EDFA (Erbium Doped Fiber Amplifier) amplifier

Separate amplifiers for C-band and L-band
48
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.
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.
49
Cisco ONS 15800
•
•
•
•
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
http://www.cisco.com/warp/public/cc/pd/si/on15800s/prodlit/ossri_ds.pdf
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DWDM Network
(point-to-point)
OLA: Optical Line Amplifier
51
DWDM Network
Add-and-Drop
Note: this is a linear topology, and not a ring topology.
Chicago
λ1: to Pittsburg
λ2: to New York
Pittsburg
λ1: drop
λ2: pass
New York
52
SONET and DWDM
DWDM
terminal
ADM
ADM
DWDM
terminal
Long Hall
SONET
Chicago
SONET
SONET
DWDM
DWDM
ADM
SONET
New York
OC-3
ADM
OC-3
IP
IP
PPP
PPP
SONET
SONET
53
IP over DWDM ???
IP
IP
IP
DWDM
terminal
???
DWDM
terminal
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)
54
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