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Optical Transport Technologies and Trends

The document discusses optical transport technologies, focusing on key concepts such as wavelength division multiplexing, fiber characteristics, and various components integral to optical networks. It highlights the importance of designing optical transmission networks based on fiber topology and characteristics, including fiber loss and chromatic dispersion. Additionally, it explores different architectures for optical networks, emphasizing advancements that enhance flexibility and operational efficiency.

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Optical  Transport  Technologies  and  Trends August  20,  2015 Dion  Leung,  Director  of  Solutions  and  Sales  Engineering dleung@btisystem.com
Company  Confidential  BTI  Systems.  Distribution  of  this  document  is  not  permitted  without  written  authorization.    2 § Logical  connectivity  is  presented  between  the  routers/switches § The  underlying  “physical”  network  is  an  abstract  layer § One  often  requires  to  know  if  the  routers  have  10G,  40G,  100G   interfaces  and  how  many  of  these  interfaces  are  available In  Data/Packet  Networking  World… P P PE PE CE CE
Company  Confidential  BTI  Systems.  Distribution  of  this  document  is  not  permitted  without  written  authorization.    3 § To  engineer  an  optical  transmission  network,  one  would  need  to  know   EXACTLY  the  underlying  fiber  topology,  the  fiber  details  and   characteristics,  so  that  the  optical  layer  can  be  designed  accordingly. § Economics  of  regional  network  <>  metro  network  <>  ULH  network In  Optical  Transport  Networking  World… DWDM 40km DWDM 30km CE DWDM DWDM DWDM CE 14km 35km 10km 15km 35km
Company  Confidential  BTI  Systems.  Distribution  of  this  document  is  not  permitted  without  written  authorization.    4 § Technology  Enabler:    Wavelength  Division  Multiplexing   – A  transmission  technology  that  multiplexes  multiple  optical  carrier   signals  on  a  single  fiber  by  using  different  wavelengths  (colors)  of   laser  light  to  carry  different  signals of  frequencies. – Frequency  (in  THz)  and  wavelength  (in  nm)  are  often  used  to  label  a   wavelength  and the  frequency  of  a  signal  is  inversely  proportional  to   wavelength.  e.g.  193  x  1012 THz  or  1551.9  nm Wavelength  Division  Multiplexing  (WDM)  – Similar  to  Sharing  Spectrum  over  Air,  Except  Medium  here  is  Fiber M U X Individually   Colored   Wavelengths D E M U X Single  Transmission  Fiber Individually   Colored   Wavelengths Equally  spaced  channels  (aka  standard  ITU  grid)
Company  Confidential  BTI  Systems.  Distribution  of  this  document  is  not  permitted  without  written  authorization.    5 § Optical  light  transmitted  through  fiber  will  lose  power § Attenuation  caused  by  Scattering,  Absorption  and  Stress § Other  related  parameter:  fiber  length,  fiber  type,  transmission  bands,   and  external  loss  components  such  as  connectors  &  splices § Typical  fiber  loss:    0.20  dB/km  – 0.35  dB/km,  although  in  some   regions  fiber  loss  can  be  as  high  as  ~0.5  dB/km § Basic  Link  Budget  Engineering: – Fiber  loss +  spice  loss  +  connector  loss  +  safety  margin  ≤ Power   Budget (i.e.  Transmitted  – Received  Power) Fiber  Characteristic  #1: Fiber  Attenuation  or  Loss  (measured  in  dB  or  dB/km)
Company  Confidential  BTI  Systems.  Distribution  of  this  document  is  not  permitted  without  written  authorization.    6 Transmission  Windows: Attenuation  in  Optical  Fiber  (measured  in  dB  or  dB/km) 800 900 1000 1100 1200 1300 1400 1500 1600 Wavelength  in  nanometers  (nm) 0.2  dB/km 0.5  dB/km 2.0  dB/km C-­band  (1530  –1565  nm) L-­band  (1565  –1625  nm) Note:    Frequency  =  3  x  108 /  wavelength 850  nm  Range 1310  nm  Range Also  known  as  the  three  “Transmission”  Windows
Company  Confidential  BTI  Systems.  Distribution  of  this  document  is  not  permitted  without  written  authorization.    7 § Different  wavelengths  travel  at  different  speeds  through  a  given  fiber   causing  optical  pulses  to  broaden  or  to  “spread” – e.g.  Wavelength  Channel  #1  travels  faster  than  Channels  #2,  #3,  etc..   § Excessive  spread  can  cause  pulses  to  overlap,  and  therefore  receivers   would  have  a  hard  time  to  distinguish  overlapped  pulses § The  longer  the  distance  (or  the  higher  the  bitrate)  is,  the  worst  the   spread  would  be. Fiber  Characteristic  #2: Chromatic  Dispersion  (measured  in  ps /  km-­nm)
Company  Confidential  BTI  Systems.  Distribution  of  this  document  is  not  permitted  without  written  authorization.    8 Lego  Blocks  of  a  Simple  Point  to  Point  DWDM  System Transponder Muxponder Transceiver Mux Demux
Company  Confidential  BTI  Systems.  Distribution  of  this  document  is  not  permitted  without  written  authorization.    9 § Multiplex  /  Demultiplexer (aka.  Mux/Demux)  Comes  with  Various  Sizes… – Use  light’s  reflection  and  refraction  properties  to  separate  and  combine  wavelengths  from  a   fiber  strand  (e.g.  logically  think  of  a  prism) – Common  technologies:  thin  film  filters,  fiber  bragg gratings  and  arrayed  waveguides  (AWG) – Passive  device  which  requires  no  power – Higher  the  channel  counts  means  higher  the  insertion  loss Lego  Block  to  Create  the  Highway  Lanes   Common  Mux/Demux Selections  from  most  vendors… DWDM  Mux-­Demux (8λ Add-­Drop) CWDM  Mux-­Demux (4λ Add-­Drop) OADMs  (1,2,  and  4λ Add-­Drop) DWDM  Mux-­Demux (40λ Add-­Drop) DWDM  Mux-­Demux (96λ Add-­Drop)
Company  Confidential  BTI  Systems.  Distribution  of  this  document  is  not  permitted  without  written  authorization.    10 Transponder  and  Muxponders: Converting  “Grey”  to  “Color” Transponder Muxponder Client  Signal  (Grey optics)   (e.g.  from  a  switch,  router) Line  Signal  (Color optics) (to  DWDM  mux  /  outside  plant) 10GE  LAN  PHY (STM64,  10G  FC) a  10G  Wavelength (e.g.  Channel  3) a  10G  Wavelength (e.g.  Channel  4) GbE STM16 2G  FC STM4 GbE 1  in  – 1  out Many  in  – 1  out
Company  Confidential  BTI  Systems.  Distribution  of  this  document  is  not  permitted  without  written  authorization.    11 Transceivers § Typical  Line  Rates – 2.5G – 10G – 100G § Transceivers – SFP – XFP/SFP+ – QSFP+ – CFP § Selection  of  which  type  mainly  depends   on  Speed,  Reach – 850nm,  1310nm,  1550nm,  CWDM,  DWDM  Fixed  Channel,  DWDM  Tunable § Each  type  of  transceiver’s  has  its  transmit  power  and  receive  power  sensitivity (e.g.  TX  =  [-­3,1]  dBm,  RX  =  [-­25,  -­5]  dBm)  à Max  Budget  =  1-­(-­25)  =  26dB Optical  Transceivers  – The  Pluggable  Optics
Company  Confidential  BTI  Systems.  Distribution  of  this  document  is  not  permitted  without  written  authorization.    12 Additional  Lego  Blocks  of  Multi-­Node  Linear  DWDM  System Transponder Muxponder Transceiver Mux Demux Optical Amplifier Dispersion Compensation
Company  Confidential  BTI  Systems.  Distribution  of  this  document  is  not  permitted  without  written  authorization.    13 Overcome  Fiber  Attenuation…   Optical  Amplifiers  (EDFA  and  Raman) Optical  Amplifiers  are  Needed  in  Order  to  be  Sure  Optical   Signals  Can  Be  Accurately  Detected  by  Receivers Two  Common  Types  of  Optical  Amplifiers Erbium  Doped  Fiber  Amplifier RAMAN  Amplifier Most  common  used  and   simple  to  deploy Fixed  gain  or  Variable  gain   For  high  span  loss  and  long   distance  transmission Used  in  Conjunction  With   EDFAs
Company  Confidential  BTI  Systems.  Distribution  of  this  document  is  not  permitted  without  written  authorization.    14 End End 0 Max Min Receiver Tolerance CD Dispersion  Compensation  Over  Multi-­span  Route (Note:  for  100G  coherent transmission,  CD  is  less  of  an  issue…) DCM DCM DCM Span-­by-­Span  CD  Compensation  for  10G/40G  transmission   Simply  match  fiber  distance  to  DCM  type  (e.g.  Use  60km  DCM  for  ~60km  link)  
Company  Confidential  BTI  Systems.  Distribution  of  this  document  is  not  permitted  without  written  authorization.    15 As  Network  Grows  and  Evolves  to  Ring  /  Mesh  Topologies… Advanced  Technology  Enabler  Makes  Operation  &  Planning  Simpler From  www.datacentermap.com
Company  Confidential  BTI  Systems.  Distribution  of  this  document  is  not  permitted  without  written  authorization.    16 § For  initial  Point-­to-­Point  network,  Fixed  OADM  (FOADM)  network   architecture  worked  fine. § A  problem  arises  when  we  have  intermediate  location  that  requires   “partial”  adding/dropping  of  traffic  à manual  patch  work  is  needed Unexpected  Network  Expansion  or  Node  Insertion Wavelength  power  management  can  become  tricky  to  engineer A C 40km 10dB B 20km 5dB § 10  x  10GbE  circuits  are  now  between  Site  A  and  Site  B   § 10  x  10GbE  circuits  are  now  between  Site  A  and  Site  C  (via  Site  B) 10  x  10GbE 10  x  10GbE
Company  Confidential  BTI  Systems.  Distribution  of  this  document  is  not  permitted  without  written  authorization.    17 § Since  not  all  wavelengths  need  to  be  dropped,  manual  padding,  patching  works   are  required  to  connect  wavelength  across  intermediate  site(s) § Patching  through  makes  sense  for  small  λ counts,  but  with  40/96  DWDM   channels,  this  can  be  prone  to  human  errors  and  difficult  to  manage  – a  better  solution  is  warranted.   A  Closer  Look:  Channel  Patching  Work  is  Required Intermediate  Site  (at  Site  B) DEMUX MUX λ λ λ λ λ λ λ λ λ λ 1.  The  insertion  loss affects  the  overall  link  budget 2.  Each  wavelength  added needs  to  be  re-­balanced λ 3.  Regeneration  is  often needed  due  to  deficit  power  budget From  Site  A                                                                                            At  Site  B                                                                                  To  Site  C
Company  Confidential  BTI  Systems.  Distribution  of  this  document  is  not  permitted  without  written  authorization.    18 How  a  4-­Degree  ROADM  Node  Works… A/D Ex2 Ex4 Ex3 R O A D M Fiber Line A/D Ex3 Ex2 Ex4 R O A D M Fiber Line A/D Ex2 Ex4 Ex3 R O A D M Fiber Line λ Mux  /  Demux λ λ A/D R O A D M Fiber Line Ex2 Ex3 Ex4 Mux  /  Demux λ λA  Single  Express Cable Automatic Power Equalized Wavelengths In-­Service  Network   Expansion  by  Simply Adding  ROADM  module
Company  Confidential  BTI  Systems.  Distribution  of  this  document  is  not  permitted  without  written  authorization.    19 Network-­wide  Benefit  of  ROADM:   Reconfigurability,  Flexibility  and  Ease  of  Expansion • Individual  wavelengths  can  be  easily  steered  from   any  node  to  any  node   • Site  visit  only  at  the  add/drop  locations • Simplify  operations  and  network  planning O O O OO O
Company  Confidential  BTI  Systems.  Distribution  of  this  document  is  not  permitted  without  written  authorization.    20 Optical  Layer Lego Block Uses  &  Benefits Additional  Design  Notes Fiber  Pair For  DWDM  transmission • G.652  /  SMF  is  preferred Mux  /  Demux (M/D) For  dividing  fiber  into  virtual   highway  lanes  or  wavelength channels • Passive element  (no  power   required) • Various  M/D  have  different   insertion  loss Dispersion Compensation   Fiber   or  Module   (DCF/DCM) For  compensation   CD  for 80km  or  longer span  or  multi-­ span  network • DCF  is  usually  classified  by   distance • DCF  has  insertion  loss  and   add  latency Amplifier For  overcoming fiber  span   loss  and  minimizing   regeneration   cost  for  multi-­ span  network • Choice  of  EDFA  (commonly   used  metro)  and  Raman  (for   regional/long-­haul) • Amplifier  has  various  gain   levels,  noise  figure Reconfigurable Optical  Add/Drop   Multiplexer (ROADM) For  flexible  wavelength   add/drop/bypass  and  simpler   operation • Single  module  combines   amplifier  and  WSS • Per-­channel  auto  power   balancing Summary  of  Essential  Lego  Blocks  for  Building  a  Flexible   Optical  Network
Company  Confidential  BTI  Systems.  Distribution  of  this  document  is  not  permitted  without  written  authorization.    21 DWDM 40km DWDM 30km CE DWDM DWDM DWDM CE 14km 35km 10km 15km 35km § One  school  of  thought:  Router  vendors  have  integrated  DWDM  or  color  optical   interfaces  onto  their  routing  platform § Another  school  of  thought:    Optical  vendors  have  integrated  packet  functionalities   (L2/L3)  onto  their  optical  platform § Which  option  is  better?  Which  option  is  more  cost  effective?  It  depends. Remember  this  View? P P PE PE CE
Company  Confidential  BTI  Systems.  Distribution  of  this  document  is  not  permitted  without  written  authorization.    22 School  of  Thought  #1…  Simple  Point  to  Point Converged  Packet  Optical  Networking   Edge Router Core   Router Core   Router § Optics  on  routers  simplify  the  need  for  a  separate  optical  platform § Limited  to  point-­to-­point  or  simple  fiber  topology.  Remember  the   fundamental  optical  rules  and  lego blocks  don’t  disappear.   § Optical  reach  depends  on  the  integrated  optical  transceiver  specifications § 100G  coherent  technology  helps  overcome  dispersions Integrated  Optics  on  Routers Edge Router
Company  Confidential  BTI  Systems.  Distribution  of  this  document  is  not  permitted  without  written  authorization.    23 School  of  Thought  #2…  Beyond  Point  to  Point Converged  Packet  Optical  Networking   NMS Edge Router Core   Router Core   Router § Pre-­integrated  solution  using  10G/100G  colored  interfaces  from  existing   feature-­rich  routing  platform,  or  grey  optics  handoff § ROADM  layer  can  provide  additional  layer  of  flexibility  at  physical  layer § OSS/NMS  integration  can  simplify  operations  and  troubleshooting Dynamic   ROADM  Core Edge Router
Company  Confidential  BTI  Systems.  Distribution  of  this  document  is  not  permitted  without  written  authorization.    24 School  of  Thought  #3…  DC+C  Provider  Centric Converged  Packet  Optical  Networking • If many Layer 3  features go unused in  routers,  you paid for them anyway • If most of  Layer 3  traffic is actually MPLS  LSR  switching… • MPLS  LER  features  are  higher  cost  than  simple  LSR   • Do  you use  all the RFC’s and  functionalities in  your routers today? • MPLS  LER  and  LSR  functions do  not need to  be  on same equipment LER WDM LER/LSR $$$$$ LER WDM LSR $$ LER $$ $$ $ LER WDM+LSR
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