OPTICAL COMMUNICATIONS & NETWORKING - AN OVERVIEW

8/31/11

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• 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

WADM

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

Layering Model

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The layering Model for the IP

Open Systems Interconnection (OSI) Seven-

Layer Reference Model

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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