Optical communications & networking - an Overview By: Mr. Gaurav Verma Asst. Prof. ECE NIEC

Communication Systems Basic Blocks Coverage and Topology Three basic components Source and Transmitter Destinations and Receiver Communication channel (medium) Communication channel Wired Wireless Glass Water and or materials 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 Based on circuit switching (setup, connect, tear-down) Example: Public Switching Telephone Network (PSTN) Originally only supported voice Not good for bursty traffic 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

Layering Model The layering Model for the IP Open Systems Interconnection (OSI) Seven-Layer 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 14 14

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! 15 15

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 16 16

How Data Passes Through Layers Each computer has a layered protocols

IP over ATM over SONET

IP over SONET

IP over WDM