optical communications & networking - an overview by: mr. gaurav verma asst. prof. ece niec
TRANSCRIPT
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)
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!
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