Optical networking
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Optical networking technologies provide high-speed, high-bandwidth data transmission over long distances using fiber optic cables. Key technologies include passive optical networks (PON) for access networks, SONET/SDH for metro networks, and dense wavelength division multiplexing (DWDM) for long-haul transport networks. DWDM works by transmitting multiple optical signals simultaneously on different wavelengths over the same fiber, vastly increasing network capacity. Proper layer-2 encapsulation is required to transport layer-3 protocols like IP over DWDM.
Optical networking
- 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
- 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
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- 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
- 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
Editor's Notes
- #26: http://www.hakko-opto.com/pdf/TW_300_LAN_PLUS.pdf FSAN: Full Service Access Network
- #40: As the need for more capacity increased over the years, first for voice traffic, today mostly for internet traffic, different solutions have been adopted. The simplest one is Space Division Multiplexing: it simply means to deploy and use more links of the same type. This approach is very expensive since it uses up all available resources and asks for infrastructure upgrades A more efficient solution came in with TDM technologies. In this case, we keep the same transmission medium but we increase the bit rate over it. If you go back a few years, SDH/SONET equipment, and routers as well, was transmitting at 155 Mbps, then 622 Mbps, finally 2.5 Gbps and just recently 10 Gbps. It is true that the transmission medium is always the same, but the transmission equipment is getting more and more complicated and expensive. Additionally, the maximum transported capability over a fiber pair is iin the range of a few Gbps. The way to scale to higher transported capacity is WDM. This technology keeps the same fiber, the same bit rate, but uses multiple colours to multiply transported capacity.
- #45: The majority of DWDM systems today operate in the C-Band. Moving into L next, then potentially S. CWDM operates primarily across S-C-L, with Extended Band fibers (like Allwave and SMF-28e) opening up the 1360-1460 window to support additional CWDM wavelengths.