ELG4173 Optical Communications & Networking Trevor Hall thall@site.uottawa.ca Centre for Research in Photonics 1
Optical Fibre Communications Systems: Digital Transmission Optical Fibre Communications Systems normally use digital transmission because: It is difficult to achieve SNRs large enough for good quality analogue performance The larger bandwidth required by digital systems for a given system capacity (bit rate per channel times number of channels) is readily available Centre for Research in Photonics 2
Digital Transmission: bit rates Typically systems operate at particular rates in an agreed order of progression. Common rates (due to the domination of SONET/SDH) are: 155.5 Mbit/s (OC-3, STM-1) 622.0 Mbit/s (OC-12, STM-4) 2.5 Gbit/s (OC-48, STM-16) 10 Gbit/s (OC-192, STM-64) 40 Gbit/s (OC-768, STM-256) Centre for Research in Photonics 3
Fibre Optic Communication System: originating node Digital streams from other sources Pulse Code Modulator Formatting / Mapper Baseband signal e.g. Voice TDM Mux SERDES/Framing/Line Coding/FEC Optical Transmitter Centre for Research in Photonics 4
Dense Wavelength-Division Multiplexing Network Terminals NT NT NT NT λ1 λ2 λn-1 λn Multiplexer Amplifiers / Repeaters Monitor Points Demultiplexer λ1 λ2 λn-1 λn NT NT NT NT Wavelength Converter Wavelength Converter Centre for Research in Photonics 5
Fibre Optic Communication System: terminating node Optical Receiver TDM Demux SERDES/Framing/Line decoding/fec Digital streams to other sources De-formatting / Mapper Pulse Code de-modulator Baseband signal e.g. Voice Centre for Research in Photonics 6
PCM Centre for Research in Photonics 7
TDM Bandwidth for voice channel in telephony ~ 4kHz Sample rate ~ 8kHz (c.f. 125μs SONET frame) 8-bit code Hence 64 kbit/s must be transmitted A wavelength channel might operate at 2.5 10 Gbit/s and hence could accommodate 40,000-160,000 voice channels Clearly wasteful to use one wavelength per channel Centre for Research in Photonics 8
TDM Time Division Multiplexing is used to share a single wavelength amongst many channels. The transmitter sends a chunk of data from one channel then, while waiting for more data to arrive on that channel, the transmitter is switched to send a chunk of data from the next channel. The transmitter returns to serve each channel periodically under the control of the multiplexer circuits. Centre for Research in Photonics 9
TDM & WDM Centre for Research in Photonics 10
TDM & WDM networks Centre for Research in Photonics 11
Network topologies Centre for Research in Photonics 12
Mesh Networks Centre for Research in Photonics 13
Networks of networks of networks.. Centre for Research in Photonics 14
Generic SONET network Centre for Research in Photonics 15
Basic STS-1 1 SONET frame Centre for Research in Photonics 16
Basic STS-N N SONET frame Centre for Research in Photonics 17
SONET ADM Centre for Research in Photonics 18
2-fiber UPSR Centre for Research in Photonics 19
2-fiber UPSR Centre for Research in Photonics 20
BLSR architecture Centre for Research in Photonics 21
BLSR reconfiguration Centre for Research in Photonics 22
Four-fiber BLSR Reconfiguration Centre for Research in Photonics 23
SONET/SDH Gerd Keiser, Chapter 12.2 & references therein Centre for Research in Photonics 24
Circuit Switching: Broadcast & Select Crossbars Centre for Research in Photonics 25
Reconfigurable Optical Circuits: Route & Select Crossbars Centre for Research in Photonics 26
TDM switch n input lines 1 W bit words n output lines 1 W W TDM Mux RAM TDM Demux Centre for Research in Photonics 27
Data packet Centre for Research in Photonics 28
Packet Switched Network (Nick McKeown) R3 A R1 R4 D B E C R2 R5 F Centre for Research in Photonics 29
Output queued switch and centralised shared memory implementation n input lines 1 W bit words n output lines 1 W W TDM Mux RAM TDM Demux Centre for Research in Photonics 30
Statistical Multiplexing (Nick McKeown) Observations 1. The bigger the buffer, the lower the packet loss. 2. If the buffer never goes empty, the outgoing line is busy 100% of the time. Centre for Research in Photonics 31
How we think the Internet is (Nick McKeown) Centre for Research in Photonics 32
How the Internet really is (Nick McKeown) $6Bn $35Bn Packet Switched (IP routers) Circuit Switched (SONET) Centre for Research in Photonics 33
How the Internet really is (Nick McKeown) Your Local CO IP routers SONET/SDH IP routers Your Local CO Centre for Research in Photonics 34
What happens when you make a telephone call? Credit to Melanie Holmes Centre for Research in Photonics 35
4-layer school bus model Centre for Research in Photonics 36
Protocol Stacks Source Node Application Layer Intermediate Node amplifier/repeater switch/bridge router Destination Node Application Layer Transport Layer Transport Layer Network Layer Network Layer Network Layer Data Link Layer Data Link Layer Data Link Layer Physical Layer Physical Layer Physical Layer Centre for Research in Photonics 37
IP Application Layer TCP UDP IP Ethernet Physical Layer Centre for Research in Photonics 38
Optical Networks Today Application Application Layer Application Layer IP IP IP ATM PPP Ethernet MAC SONET SONET Ethernet PHY WDM WDM WDM Centre for Research in Photonics 39
Photonic Networks Tomorrow? Application IP The optical layer must provide its client layers with the services formerly offered by SONET e.g. Optical Channel Monitoring Protection & Restoration Circuit Switching TDM WDM Centre for Research in Photonics 40