OPTICAL COMMUNICATIONS &
NETWORKING - AN OVERVIEW
By:
Mr. Gaurav Verma
Asst. Prof.
ECE
NIEC
Communication Systems
Basic Blocks
• Three basic components
• Source and Transmitter
• Destinations and Receiver
• Communication channel
(medium)
• Communication channel
• Wired
• Wireless
• Glass
• Water and or materials
Coverage and Topology
• Coverage (public network)
• LAN
• MAN
• WAN
• Topology
• Bus
• Ring
• Mesh
• Star
Changing Service Landscape
• Network characteristics
• Full redundancy
• Fast restoration
• High availability (99.999 %)
• Low latency
• High bandwidth
• Dynamic allocation and high bandwidth efficiency
• Support various services
• More providers and equipment builders (due to Deregulation of
the telecom industry)
• Providers are expected to provide more services at higher
capacity at lower prices!
• A positive feedback business model!
• Need for high capacity network
• More users
Service Types
• Two basic service types (switching technologies)
• Connection-oriented
• Connectionless
• Connection-oriented
• Based on circuit switching (setup, connect, tear-down)
• Example: Public Switching Telephone Network (PSTN)
• Originally only supported voice
• Not good for bursty traffic
• Connectionless
• Based on sending datagrams
• Examples: Packet, massage, burst switching
• Improves bandwidth and network utilization
Multiplexing
• Transmitting several signals over a single communications
channel
• Multiplexing technologies
• Frequency Division Multiplexing (modulating data into different carrier
frequencies)
• Wavelength Division Multiplexing
• Time division Multiplexing (dividing available time among various
signals)
• Statistical Multiplexing (dynamic allocation of time spaces depending
on the traffic pattern)
• Statistical Multiplexing
• Requires buffering resulting in variable delay
• Many packets will have to be buffered
• Packets will have to be delayed
• Some packets may be lost
• Guarantee of Service (QoS)
Multiplexing
Optical Fiber
• Allowing transmission of information using pulses of light
• Advantages
• High bandwidth
• Low noise
• Low interference (electromagnetic)
• Optical fiber installation
• Measured in fiber sheath-miles (or fiber miles)
•
Example: we install 3 fiber cable within 10 mile long route;
each fiber cable has 20 fibers  we have 600 fiber miles 30
cables
• Currently more than 1.5 billion kilometers of optical fiber is
deployed around the world [1]
• The circumference of earth is 40,000 Km!
[1] http://www.corning.com/opticalfiber/innovation/futureoffiber/index.aspx
Evolution of Optical Networks –
First Generation
• Started in 1980
• Limited to fiber optic transmission systems – the rest of
the system was electrical
• Thus, the electronic was the major bottleneck!
• The received optical data had to be dropped and then transmitted –
this was a point-to-point system
• Example: Synchronous Optical Network (SONET) and
Synchronous Digital Hierarchy (SDH), Fiber Distributed Data
Interface (FDDI), Fiber Channel
• These systems where based on Optical TDM (10Gb/s and 40Gb/s)
• Higher capacity systems were build using WDM technology (1
Tb/s) – remember a single phone line is only 60 Kb/s!)
Evolution of Optical Networks –
Second Generation
WADM
• Incoming optical signals could be
switched in optical domain (optical
switching)
• No longer limited to point-to-point
• Underlying technologies included
• Optical Add-Drop Multiplexers (OADM)
• Optical crossconnets (OXC)
• Optical line terminals (OLT)
• Wavelength Add/Drop Multiplexer (WADM)
• Dense WDM (DWDM)
• Examples
• FTTH, FTTC, ROADM
OXC
Evolution of Optical Networks –
Third Generation
• All optical packet switching
• All packets are processed in optical domain
• Transparent to the service
• Handle any arbitrary bit rate
• Underlying technologies
• Optical buffering!
• Fast switching
So far, no optical networks have been available!
Optical Networking
Comparing Different Optical Nodes
Optical Packet Switching
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Layering Model
Open Systems
Interconnection
(OSI) SevenLayer Reference
Model
The layering Model for the IP
Protocol Suites and Layering Models
• Physical Layer (Layer 1)
• specify details about the underlying transmission medium and
hardware
• all specifications related to electrical properties, radio frequencies,
and signals belong in layer 1
• Network Interface (or Data Link) Layer (Layer 2)
• Network (physical) addresses
• maximum packet size that a network can support
• protocols used to access the underlying medium
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Protocol Suites and Layering Models
• Internet Layer (Layer 3)
• protocols specifying communication across the Internet & routing
specifications (spanning multiple interconnected networks)
• Logical addressing and path determination
• Transport Layer (Layer 4)
• Includes specifications on
• controlling the maximum rate a receiver can accept data (flow control)
• mechanisms to avoid network congestion
• techniques to insure that all data is received in the correct order
Remember: Each layer contains its own specifications & protocols!
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Protocol Suites and Layering Models
• Application Layer (Layer 5)
• specify how a pair of applications interact when they communicate
• specify details about
• the meaning of messages that applications can exchange
• the procedures to be followed to execute the application
• Some examples of network applications in layer 5
• email exchange
• file transfer
• web browsing
• telephone services
• and video teleconferencing
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How Data Passes Through Layers
Each computer has a
layered protocols
IP over ATM over SONET
IP over SONET
IP over WDM