1. Optical Networking

2. Drivers of Optical Networking
Number of factors involved in deployment of Optical Network
Improved performance
Speed is doubled in every 9 months for every dollar spent.
No. of bits/s/lamda (λ) doubles every 12 months
No. of transistors on computer chips are doubled in every 18 months
DWDM (Dense Wavelength Division Multiplexing) enables multiple wavelength to be carried over a single strand of fiber
Performance of optical infrastructure (Cost per mile) improved up to 320 km (200 mile) after which signal is regenerate, reshaped, resynchronized and retimed
Optical switches will automate the provisioning as well as boosting the capacity for end-to-end optical networking

3. End-to-End Optical Networking
Nowhere in the network there will be conversion of optical signal to electrical signal
Cost reduction and improved performance
Improved bandwidth from Gbps equipment to Tbps fiber speed if conversion at terminal equipment can be avoided
For an end-to-end, the network will require
Optical Line Amplifiers:
WDM Equipment
OADMs (optical add/drop multiplexer)
Optical Switches
Integrated photonic circuits

4. End-to-End Optical Networking: Optical Line Amplifiers
Erbium-doped fiber amplifier (EDFA)
Raman amplifier
Semiconductor optical amplifier (SOA)
EDFA – overcome the limitation of optical-to-electrical conversion (extraction, retiming and regeneration) and improved the speed to 10Gbps
Consists of a erbium doped fiber, a laser diode, couplers and isolators
Boosts the 980-nm laser light to 1550-nm
Raman amplifier – a powerful laser source to boost the signal power and overcome the wavelength limitation of EDFA
SOA – built on a single chip.
Less expensive than EDFA, but high SNR

5. End-to-End Optical Networking: WDM Equipment
WDM – separates or multiplexes different λ into a single fiber
Normal WDM
Coarse WDM (CWDM)
Dense WDM (DWDM)
Differs in type of light source, spacing between wavelengths, no. of channels, supported distance and type of amplifiers.
WDM – uses the two normal wavelengths 1310 and 1550 on one fiber
CWDM – developed for metropolitan area network. Less expensive and supports up to 16 channels across multiple transmission over silica fibers.
DWDM – supports C-Band (1530 nm-1560 nm) transmission with denser channel spacing. Channel plans vary, but a typical DWDM system would use 40 channels at 100 GHz spacing.
Uses Raman amplifiers tighter channel spacing
Suitable for point-to-point links and long haul pipes
Requires precise lasers and channel separators

6. End-to-End Optical Networking: OADM
OADM – a set of special filters to extract the wavelength to be dropped off
Less expensive, supports reconfiguration and suitable for real-time provisioning
Reconfigurable OADM (ROADM) – a device to add or drop traffic depending on a fiber network
Switching traffic on demand at SDH/SONET and wavelength layers
Allows remote configuration and reconfiguration
Supports automatic power balance as routing of signals is not provisioned beforehand

7. End-to-End Optical Networking: Optical Switches
Optical switches are also know as optical cross-connects or wavelength router that directs light beams from one fiber to another.
Resides at junction points of optical network to combine wavelengths for end- to-end connections
Provides flexibility and reliability
Supports network management activities such as optical-layer restoration and reconfiguration, dynamic wavelength management and automated optical-layer provisioning
Key issues for selecting optical switches
Number of ports – can scale to as many as 1000 ports
Automation – should support remote real-time provisioning
Granularity – can handle small as well as large bandwidth
Optical switching categories are –
MEMS (Microelectromechanical systems) switches – an array of microscopic mirrors to reflect light from one port to another
Bubble switches – uses heat to create small bubbles in fluid channels to reflect and direct light
Thermo-optical switches – light passing through a glass is heated up or cooled down to change the reflective index and bending the light to enter into another fiber
Liquid crystal display (LCD) switches – uses liquid to bend light
Tunable lasers – pumps out light at different wavelengths

8. Next Generation Digital Loop
Optical networks are used to support for SDH/SONET as well as copper connections to local exchange
Layer 2 services such as ATM, Frame Relay and Ethernet as well as Layer 3 services such as IP
This allows the integration of DSL (digital subscriber line) modem without requiring DSL access multiplexer (DSLAMs)
Multiplexed voice channels over PSTN, sent on shared ATM trunk
PON (Passive Optical Network) – an arrangement of fiber-to-the- premises (FTTP) or point-to-multipoint configuration to serve multiple customer premises
Can support two-way traffic by using separate wavelength for upstream (1310 nm) and downstream (1490 nm)
Uses passive (i.e., unpowered) splitter to split the power and route to multiple premises
Significantly reduced cost and supports 1:32 split ratio
Supports simultaneous operation of 10 Gbps Ethernet PON (GEPON) and 1 Gbps PON for downstream on the same PON which is known as 10/1 Gbps EPON

9. Overlay networking model
Problems with 1st generation optical network
Bandwidth efficiency – SDH/SONET are only for single-wavelength and TDM scheme. So, to support WDM, operators requires to use both SDH/SONET and WDM
In order to overcome the limitation of 1st generation network and to accommodate very large traffic flows, the approaches are
Overlay Model
Peer-to-peer Model
Overlay Model maintains two separate and discrete networks: a layer 1 optical network and client network
Core network is hidden from the routed network and relies on the User-to-Network Interface (UNI) for signaling to the devices at the egde
Defines a new optical transport hierarchy whose base is the optical transport module (OTM) and the initial client is SDH/SONET and other data services such as Ethernet, IP, ATM and fiber channel
OTMs can be denoted as OTM n.m. where n is the number of supported wavelengths and m is the lowest bit rate (e.g., m = 1 for 2.5Gbps, m = 2 for 10Gbps and m = 3 for 40Gbps)
OTM 3.2 indicates a channel with 3 λs operating at 10Gbps

10. Peer-to-peer networking model
Network equipment at edge decides the how bandwidth is allocated within the core
Fully visible to all the devices, but devices needs to the nearest optical switches
Routers and optical switches works as the peer and relies on GigE and 10GigE standards
Each user has a 48-bit distinct MAC (Media Access Control) address
Three standards from IEEE aimed to provide core technology for peer-to-peer model
10GigE – supports 10 Gbps at metro core and WAN specified under IEEE 802.3ae
Ethernet First Mile (EFM) – specified under IEEE ah and supports 1 Gbps at first or last mile
Resilient Packet Ring – specified by IEEE optimized for transport of data traffic over fiber ring